Hydrobiologia 428: 1–59, 2000. © 2000 Kluwer Academic Publishers. Printed in the Netherlands.
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New species of Rhynchelmis (Clitellata, Lumbriculidae), with observations on the Nearctic species S. V. Fend1,∗ & R. O. Brinkhurst2 1 U.S.
Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025, U.S.A. (E-mail:
[email protected]) Resources Center, Franklin, TN, U.S.A.
2 Aquatic
Received 7 June 1999; in revised form 21 December 1999; accepted 2 January 2000
Key words: Clitellata, Oligochaeta, Lumbriculidae, Rhynchelmis, taxonomy
Abstract The Nearctic species of Rhynchelmis (Lumbriculidae) are distinguished from the Palearctic group Rhynchelmis s. str. by longitudinal muscle bands that do not curl inwards. Six new species from western North America support the existence of two major groupings within the Nearctic fauna. Species in Group 1 are distinguished from other Rhynchelmis by large penial bulbs and multiple spermathecal diverticula. Within Group 1, Rhynchelmis yakimorum n. sp., Rhynchelmis monsserratus n. sp., Rhynchelmis gustafsoni n. sp. and Rhynchelmis utahensis n. sp. differ from the related Rhynchelmis (=Sutroa) rostrata in having short penes and spermathecae with 2 short, lobed diverticula. R. monsserratus is distinguished by a single, median spermatheca, R. gustafsoni has closely appressed, median spermathecae and atria, and R. utahensis differs in structural details of spermathecae and male pores. Rhynchelmis gilensis n. sp. has a single, median spermatheca with unbranched diverticula and distinctive nephridia. Redescription of material from the type localities of both Sutroa alpestris and R. rostrata supports their combination. Group 2, corresponding in part to Rhynchelmoides, is distinguished from Group 1 mostly by characters that are inconsistent or appear plesiomorphic. Within Group 2, Rhynchelmis saxosa n. sp. closely resembles Rhynchelmis alaskana, except for the absence of lateral blood vessels in posterior segments and distribution of prostates. Rhynchelmis elrodi and Rhynchelmis glandula consistently differ in presence of ventral glands and have different distributions, so their supposed synonymy is rejected. Abbreviations: am – atrial muscle; at – atrium; br – brain; bv – blood vessel; ch – chaeta; du – duct; ep – epidermis; f1 – anterior male funnel; f2 – posterior male funnel; ff – female funnel; fp – female pore; gl – gland; gu – gut; lm – longitudinal muscle band; mp – male pore; mu – muscle; nd – nephridial duct; nf – nephridial funnel; np – nephridopore; ov – ovary; pb – penial bulb; pe – penis; ph – pharynx; po – pore; pr – prostate; sa – spermathecal ampulla; sb – spermathecal bulb; sd – spermathecal diverticulum; se – spermathecal ectal duct; sm – septum; sp – spermathecal pore; te – testis; v1 – anterior vas deferens; v2 – posterior vas; vd – vas deferens; vn – ventral nerve cord; vv – ventral blood vessel Introduction The genus Rhynchelmis Hoffmeister, 1843, in the Lumbriculidae is generally defined as having spermathecae in VIII and atria in X. The atria are generally long and roughly cylindrical, extending into posterior segments. The prostomium usually terminates in a distinct proboscis, and the spermathecae communicate ∗ Author for correspondence
with the gut in most described species. The Nearctic species associated with the genus are distinguished from the Palearctic group comprising Rhynchelmis s. str. (Hrab˘e, 1936) by indistinct longitudinal muscle bands that do not curl inwards. Rhynchelmis s. lat. as defined here includes the genera Sutroa Eisen, 1888, Rhynchelmoides Hrab˘e, 1936, and Pseudorhynchelmis Hrab˘e, 1982. Seven species of lumbriculid worms attributable to Rhynchelmis s. lat. have been described in North
2 America, although some species have been disputed. Brinkhurst & Cook (1966) combined Sutroa alpestris Eisen, 1892, with Sutroa rostrata Eisen, 1888, and also combined Rhynchelmis glandula Altman, 1936, with Rhynchelmis elrodi Smith & Dickey, 1918. Holmquist (1976) questioned the latter combination after reexamining the type series. There has also been disagreement at the generic level. Rhynchelmis elrodi, Rhynchelmis glandula, Rhynchelmis brooksi, Holmquist, 1976, and Rhynchelmis alaskana Holmquist, 1976, have all been associated with Rhynchelmoides Hrab˘e, 1936 (Hrab˘e, 1961; Sokol’skaya, 1983). The genus Rhynchelmoides was rejected by Cook (1971) and Holmquist (1976), although it has been retained by some others (Hrab˘e, 1982; Timm, 1997). Brinkhurst & Cook (1966) also transferred the now monotypic genus Sutroa to Rhynchelmis. This was disputed by Holmquist (1976), who supported the retention of Sutroa, defined by the single median spermatheca and the large, bulbous penes. Almost all Nearctic Rhynchelmis s. lat. records are from aquatic habitats in the western part of the continent. The existing distribution data are patchy, due to difficulty in collecting these worms and to taxonomic uncertainty. Recent collections of aquatic worms in the northwestern U.S.A., spurred by interest in water quality and fish disease, have produced many specimens not attributable to existing species. In addition to new descriptions, large series of worms from many sites allow an assessment of character variability in some previously described species. A thorough cladistic analysis of the genus (Fend & Brinkhurst, in prep.) awaits verification of characters in many Palearctic species, the types of which may be unavailable. Therefore, this paper is limited to descriptions of the North American fauna, with informal groupings based on overall similarity rather than formally proposed apomorphies.
Materials and methods Most worms collected for this study were fixed in FAA or Bouin’s fluid (Pennak, 1989), and then preserved in 70% ethanol, but much of the older material was preserved differently. Sagittal sections were approximately 7 µm; transverse sections were 10 or 15 µm; all were stained in hematoxylin and eosin Y. Dissections and whole mounts were generally mounted in KleermountTM after staining with carmine or
hematoxylin. Blood vessels were observed in cleared whole worms and transverse sections, as live specimens were rarely available. Not all measurements could be made on all preparations. In general, external characters were measured with a dissecting microscope to the nearest 0.1 mm; internal characters were measured with a compound microscope to about 2 µm for small structures, or 10 µm for large structures. Reproductive structures were measured on fully-mature worms, with welldeveloped genital pores, sperm in the spermathecae and well-developed eggs; measurements of other structures were made on worms that were at least partially mature, with gonads and genital pores. Museum collections are indicated as follows: USNM=U.S. National Museum, Washington, DC; BMNH=British Museum of Natural History, London; SMNH=Swedish Museum of Natural History, Stockholm; UWBM=Burke Museum, University of Washington, Seattle. Collection data are given only for fully-mature worms, unless otherwise noted.
Taxonomy Two groups of Nearctic species can be recognized based on position of the spermathecal pores, the basic structure of the atria and spermathecae, and the presence of a nonfunctional anterior pair of vasa deferentia. These groups may or may not have significance once all characters are considered simultaneously in a phylogenetic analysis. GROUP 1: Spermathecal pore(s) in bulb-like structure(s), anterior to, and sometimes median to the ventral chaetae; often with a single, median spermatheca in VIII; multiple diverticula originating in the spermathecal duct. Male ducts terminate in penial bulbs; atria without prostates in ectal part; anterior vasa deferentia present but nonfunctional. Vasa deferentia usually enter atrial muscle layer near the midpoint. Rhynchelmis yakimorum n. sp. Holotype: USNM 186440, a sagittally sectioned specimen. Type locality: Washington: Kittitas Co.: Yakima River below Umtanum Creek, in a shallow riffle, 12.XII.1996.
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Figure 1. R. yakimorum, drawing of whole worm from type locality (a) mature (b) partly mature.
4.XI.1990. Two whole mounts. Yakima River near Ellensburg, 26.X.1987. Two whole mounts, 7 in alcohol. Yakima River near Cle Elum, 4.XI.1990. Two dissected, 1 whole mount, 2 in alcohol. 3.XI.1988. One whole mount. Cle Elum River near mouth, 2.XI.1990. Two whole mounts. Taneum Creek near mouth, 4.XI.1990. One dissected, 2 in alcohol. Yakima Co.: Yakima River near Pomona, 2.XI.1988. Two whole mounts, 1 dissected, 5 in alcohol. All collections by S. Fend. Etymology: yakimorum from the Yakima people of the area. Description Figure 2. R. yakimorum, chaetae, from type locality.
Paratypes: USNM 186441–186444: From the type locality, 2 sectioned worms (1 transverse, 1 sagittal), 12.XII.1996. Two partially dissected specimens on slides, 6 in alcohol, 10.XII.1994. P. Rodriguez collection: LUM002, 2 whole worms in alcohol, 10.XII.1994. Other material: Washington: Kittitas Co.: From the type locality, various dates (all November to March, 1988–1996). Twenty one sectioned, 16 dissected, many in alcohol. Yakima River near Thorp,
Large worms, measurements in Table 1. Color of living worms dark reddish to pinkish; preserved worms pale, unpigmented. Prostomium with a distinct proboscis, about 1 mm long by 0.1 mm, constricted at intervals but not distinctly ringed. Anterior segments nearly circular in transverse section, without prominent longitudinal ridges. Segmentation slightly to moderately developed, and secondary annulation usually apparent in anterior segments beginning with II or III. Clitellum usually prominent, without obvious annulation, from IX to XIV or XV. Chaetae simple-pointed, sigmoid, with a moderate to strong distal hook; nodulus distal to midpoint on all chaetae,
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Figure 3. R. yakimorum from type locality; head and pharynx reconstructed from sagittal sections.
Figure 4. R. yakimorum, sacs on septa in IX and X.
0.4–0.3 of chaeta length from tip (Figure 2). Anterior dorsal chaetae as short as 150 µm, others usually near 250 µm long; maximum length near clitellum. Chaetal formula aa:bc:dd approximately 3:4:4. Paired spermathecal openings anterior to ventral chaetae in VIII, slightly inside the chaetal line ventrally, usually separated by 0.2–0.4 mm, but sometimes connected by a fold (Figure 1a,b). Male pores on or slightly inside chaetal line, posterior to the ventral chaetae in X, within a pair of slits separated by about 0.2 mm (Figure 1a,b). Female pores indistinct at 11/12, on chaetal line. Epidermis 30–50 µm thick anteriorly, may be over 100 µm thick in clitellum. Body wall longitudinal muscles 50–120 µm thick anteriorly, less in the clitellar region; circular muscles 10–20 µm. Eight poorly-defined longitudinal muscle bands do not curl inward at the edges (Figures 6 and 8). Brain medially emarginate, in the peristomium with prominent anterodorsal and anteroventral nerves in addition to major ventral nerves that join in II. Pharynx mostly in
Figure 5. R. yakimorum from type locality; spermatheca, sagittal section with sperm in diverticula.
II–V, eversible, without strongly differentiated dorsal pad (Figure 3). Pharyngeal glands from IV to VI, attached to the posterior septum and dorsolaterally to the body wall, often smaller glands in III and VII. Dense clusters of cells (apparently tightly folded sacs) usually paired in IX and X, and often in VIII, lateral and slightly ventral to the gut, originating in sphincters in anterior septa; septum at base of sphincter connected to the ventral body wall by muscle (Figure 4). Similar, but smaller, structures may project forward from rear ventral aspect of 8/9, 9/10 or 10/11.
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Number of segments
Length, mm
Width in X, mm
Chaetal length, mid-body, µm
Prostates begin (segment no.)
Atrium end (segment no.)
Atrium diameter, ectal part, µm
Atrium diameter, ental part, µm
Atrial muscle, ectal thickness, µm
Atrial muscle, ental thickness, µm
Penial bulb diameter, µm
Spermathecal bulb diameter, µm
Spermathecal ampulla width, µm
Table 1. Measurements (median, range, and number of observations) of Rhynchelmis species and variants.
R. yakimorum all sites
median range n
117 68–216 44
29 10–68 64
1.1 0.6–1.7 106
245 200–320 16
12 10–16 81
16 13–23 77
80 50–120 28
65 40–110 20
12 8–30 28
5 2–6 18
415 220–550 42
330 180–450 41
130 80–210 32
R. yakimorum variant 1 Klamath River
median range n
114 52–158 15
32 19–48 13
1.1 0.7–1.5 17
200 180–230 3
12 11–15 9
17 12–20 9
65 60–70 3
50 50–65 3
13.5 12–15 2
5 4–6 3
285 200–370 6
295 240–320 4
120 120–140 4
R. yakimorum variant 2 all sites
median range n
108 80–156 25
35 16–50 25
1.6 0.7–2.3 37
215 200–320 10
12 10–16 26
14 11–22 24
58 48–90 14
50 43–67 13
9 6–14 14
2 2–5 13
350 230–580 15
270 210–420 13
81 62–131 12
R. monsserratus all sites
median range n
106 48–160 27
29 17–51 28
1.4 0.8–1.8 43
250 190–290 19
13 11–16 57
16 13–21 55
80 50–100 25
70 50–100 22
15 4–20 24
5 2–5 18
420 250–660 34
355 230–650 32
150 100–210 27
R. gustafsoni all sites
median range n
108.5 48–154 47
30 18–50 45
1.2 0.86–1.8 64
260 220–300 14
13 10–15 43
16 13–2 1 36
82 60–115 24
66 50–80 15
12 10–30 23
3 3–8 11
390 300–540 19
320 220–410 24
123 80–170 21
R. utahensis all sites
median range n
92.5 52–125 30
29 16–46 34
1.2 0.9–1.9 43
240 200–280 23
14 12–15 55
17 13–22 53
68 55–85 28
75 60–100 22
5 4–7 27
3 2–4 13
340 240–550 37
290 210–430 35
260 180–360 30
R. rostrata typical all sites
median range n
128 85–203 85
41 21–64 87
1.3 0.8–1.9 102
290 180–370 29
14 11–17 81
20 14–26 60
89 62–120 46
80 60–120 27
10 3–20 43
3 2–10 23
280 120–400 44
250 136–480 50
440 200–800 44
R. rostrata variant 1 all sites
median range n
94.5 83–108 6
23 18–32 7
1.2 0.9–1.4 13
245 140–280 8
13 11–14 25
16 13–24 20
80 65–100 16
70 60–90 9
9 5–12 16
2 2–3 9
330 250–480 15
230 150–450 21
400 270–640 17
R. gilensis all sites
median range n
72 40–91 37
16 8.5–26 40
0.62 0.33–0.8 44
165 120–185 19
11 10–12 42
1l 10–12 35
70 48–100 16
50 36–66 13
2.5 2–5 18
2 1–4 14
160 95–245 17
90 70–130 28
93 74–110 19
R. elrodi all sites
median range n
112 50–186 79
30 12.5–71 81
1.2 0.8–1.8 104
260 200–340 27
10 10–13 69
15 11–22 65
68 48–140 30
110 60–170 25
5 2–14 32
7 3–20 28
130 80–200 31
N/A
200 100–310 33
R. glandula all sites
median range n
117 89–160 21
31 16–50 22
1.2 0.8–1.5 25
250 210–280 7
10 10 11
17 15–20 12
90 50–120 7
130 80–190 7
2.5 2–7 6
3 2–4 7
170 130–200 4
N/A
255 130–300 7
to 190
to 80
nr 230
10
15
50–70
100–150
2
3
N/A
N/A
290
93.5 45–127 42
24 10–45 47
175 145–200 26
11 10–11 43
13 10–15 35
80 60–110 19
210 120–310 19
3 2–4 11
2 2–3 12
N/A
N/A
280 160–560 15
R. alaskana holotype R. saxosa all sites
median range n
0.7 0.35–1.1 74
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Figure 6. R. yakimorum from type locality; transverse section in VIII, spermathecae.
Figure 7. R. yakimorum from type locality; drawing of spermatheca from sagittal disssection.
Ventral blood vessel divides in VII, forming parallel branches connected to dorsal vessel in II–VI via 1 pair of convoluted commissural vessels. The posterior of 2 lateral vessel pairs also joins dorsal and ventral vessels in VII to about XII; the anterior pair is connected only to the dorsal vessel. Posterior to VIII, anterior pair of lateral blood vessels bears long branches ending in body wall laterally and ventrally. Posterior pair of lateral vessels with few short branches in first few segments posterior to VII. In more posterior segments, both lateral vessel pairs usually with several long branches and neither connects directly to the ventral vessel. Very short, blind branches usually present in dorsal part of each lateral vessel. Posterior to about
XX, 1 branch of each anterior lateral vessel connects ventrolaterally to the gut plexus; posterior to about XLV each posterior lateral vessel has a more lateral gut connection. In X–XII, the posterior lateral vessel enters the sperm and egg sacs, as a loop that extends through several segments (Figure 11a). Gut plexus with short connections to the dorsal and ventral vessels. Each segment with 2–3 blood glands between ventral vessel and gut plexus from VIII to at least XVI. Nephridia usually paired in most segments beginning in XIII–XV; exceptional individuals may have a nephridium in a segment anterior to X. Nephridia with small anteseptal funnel; postseptal portion a granular, bulbous structure with indistinct ducts followed by irregular ducts that loop dorsally to near the dorsal blood vessel (following the anterior lateral blood vessel), and laterally to the ventral vessel (following the inner branch of the anterior lateral vessel), where it forms a convoluted mass that may communicate with adjacent segments. A relatively straight ectal section of tubule ends in an inconspicuous nephridopore just anterior to the chaetal bundles (cf. Figure 59). Testes paired in X, ovaries paired in XI, largely within the egg sacs. Female funnels prominent at 11/12, pores intersegmental. Sperm sacs to as far as XXXIX in mature worms. Sperm sacs confluent with egg sacs, to as far as XLIV. Mature eggs, or sometimes ovary, may displace sperm sacs in some segments. Sperm and egg sacs pass through septa via openings similar to those associated with sacs/cell masses in VII–X. Spermathecae penetrate middle of ventral, longitudinal muscle bands of body wall (Figure 6), each pore
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Figure 8. R. yakimorum from type locality; transverse section in X, penial bulbs.
Figure 9. R. yakimorum from type locality; drawing of penial bulb, from sagittal dissection.
in a transverse fold with cuticular lining, surrounded by a bulbous thickening. Bulbs separated medially, with normal epidermis and part of the longitudinal muscle band between them; actual spermathecal pores separated by about 0.5 mm. Bulbs nearly spherical, approximately 300–400 µm wide, with outer layer composed of possibly glandular (not distinctly granular) cells interspersed with muscle fibers; inner layer (surrounding the ectal duct and fold) formed by anuc-
leate extensions of these cells (Figures 5 and 6). No other glands associated with the pores. Muscle fibers from the bulb extend as diffuse, dorsolateral muscles to the anterior septum and the body wall. Spermatheca with median, pyriform or cylindrical ampulla up to half the diameter of the bulb, communicating with the gut entally. Paired anterior and posterior diverticula, each near 400 µm long, with 3–5 short lobes in fan-like array, open into ectal duct at pore, inside bulb (Figure 7). Both diverticula and ampulla with thin outer muscle layer near 3 µm, and uneven inner cell layer to 30–40 µm thick. Short ectal duct near 50 µm wide and 100 µm long, with unmodified cuboidal cells. Sperm with heads lined up along margin in both diverticula and ampulla (Figure 5). Partially mature spermatheca with short diverticula and narrow ampulla. Male pores within sac surrounded by thick-walled, roughly spherical penial bulb, approximately 400 µm wide, laterally interrupting the ventral muscle band (Figure 8). Bulb composed of darkly-staining cells that are possibly glandular but not strongly differentiated, interspersed with muscle fibers. Cells in outer part of bulb may form tightly-packed, pear-shaped bundles with narrow extensions, similar to prostates. Muscle fibers weakly coalesce and extend anteriorly and dorsally to anterior septum and body wall. No distinct glands associated with male pores. Ectal end of male duct enters penial bulb dorsally. Retracted penes very short but distinct, apparently formed from extensions of cells in bulb, length 0.2–0.3 times width, directed forward and slightly laterally within sac (Figures 9 and 10). Atria narrow and cylindrical, extending
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Figure 10. R. yakimorum from type locality; sagittal section in X and XI.
Figure 11. R. yakimorum from type locality; transverse sections of atrium, (a) ectal portion, in XIII (b) ental portion, with prostates.
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Figure 12. R. yakimorum variant 1, from spring near Klamath River, California; drawings of whole worms (a) mature (b) partly mature.
through at least 3, and up to 12 segments, except when strongly convoluted. Ectal part of each atrium with thin outer layer of cells surrounding a muscle coat that is 10–25 µm thick (Figure 11a). Ental part of atrium longer than ectal portion, usually beginning in XII or posterior, with prostate cells in well-defined, stalked, pear-shaped groups penetrating the thin (2–5 µm) muscle coat (Figure 11b). Atrial lining cells near cuboidal, not granular. Anterior male funnels small (100–150 µm wide), convoluted at full maturity, not associated with testes. Anterior vasa deferentia usually less than 20 µm diameter, pass over penial bulb and join atrial muscle coat near the midpoint, usually travel inside muscle coat and open into atrium apically. Posterior male funnel of each atrium large and convoluted, 300–400 µm wide at maturity, on 9/10. Posterior vas deferens slightly wider than anterior (diameter 15–35 µm), usually enters atrial muscle coat before the anterior vas, soon after beginning of prostates, and opens into atrium immediately or after travelling inside muscle coat for up to 2 segments. The material The description of external features is based on a large series of whole specimens in alcohol; observations of internal structures are based on over 50 fully mature, sectioned or dissected specimens. Most specimens were obtained from bulk samples of the benthos. Consequently, they were badly fixed or had to be dissected to remove grit from the gut; therefore, some histological details were not clear on most individuals. Living
worms were not available, which limited observations of the vascular system. Three of the mature specimens seen had an additional unpaired spermatheca in VIII, without sperm. Less-mature specimens had spermathecae of the same general form, but with much smaller diverticula and narrower ampulla; these also had atria that were more coiled and extended back fewer segments, and penes were not apparent. All Rhynchelmis collected from the middle portions of the Yakima River, including partly-mature worms, had widely-separated, paired spermathecae in VIII, anterior to the chaetae, and male pores on or near the chaetal line. However, partlymature Rhynchelmis specimens from a headwater site and from all lower reaches more closely resembled the Group 2 species in the placement of genital pores. Rhynchelmis yakimorum variant 1 Material examined: California: Siskiyou Co.: Small springs near the Klamath River, near Happy Camp, 13.XII.1996, coll. S. Fend. Two sectioned worms (transverse and sagittal), 1 whole mount, 2 dissected, 1 in alcohol. 5.IV.1997, 1 dissected, 1 mature and several partially mature worms in alcohol. Possible records: IDAHO: Goose Creek Meadow, 20.VIII.1921. USNM 26346, 1 partially mature whole mount, 2 partially mature in alcohol (previously identified as R. elrodi). OREGON: Deschutes River at S. Junction Rd., 26.X.1995, coll. S. Fend. One partially dissected whole mount.
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Figure 13. R. yakimorum variant 1, transverse section in VIII, spermathecal bulbs.
Vascular system and nephridia as described for typical R. yakimorum. Nephridia begin XIII to XVII; paired, single or absent in posterior segments. Spermathecae paired, with closely appressed ectal bulbs inserting inside ventral muscle bands of body wall (Figure 13). Spermathecal bulb slightly depressed dorsoventrally, with shallow opening; ampulla not exceeding 1/2 diameter of bulb; diverticula with 3–5 lobes (Figure 14). Penial bulbs well separated, near spherical; male pores directed medially within sacs, without apparent penes when retracted (Figures 15– 17); associated muscles relatively distinct. Penial and spermathecal bulbs often in deeper fold than other yakimorum variants (Figures 13 and 14). Remainder of male duct as described for R. yakimorum; measurements in Table 1.
Figure 14. R. yakimorum variant 1, drawing of spermatheca, from sagittal dissection.
Description Spermathecal pores of mature worms nearly contiguous within a large, oval, median depression that extends to near the chaetal line (Figure 12a), but visible as separate pores inside the chaetal line, separated by about 0.15 mm in partially mature worms (Figure 12b). Male openings separated by about 0.4 mm, slightly inside chaetal line in external view. Other external characters as described for typical R. yakimorum; measurements in Table 1.
The material The collection from Idaho, previously identified as R. elrodi (Brinkhurst & Cook, 1966), did not contain specimens mature enough to fully describe. However, two specimens were mature enough to observe the distinctive spermathecal and penial bulbs, as well as the lobed spermathecal diverticula, and externally they resembled the California specimens. Possible additional specimens were the aberrant worm from a R. monsserratus population (see below), and a single worm collected with a large series of R. rostrata from the Deschutes River, Oregon. This last record is also inconclusive because the worm was in poor condition, although mature.
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Figure 15. R. yakimorum variant 1, transverse section in X, penial bulbs.
Figure 16. R. yakimorum variant 1, penial bulb, sagittal section.
Rhynchelmis yakimorum variant 2
Description:
Material examined: Oregon: Umatilla Co.: Spring along Bear Wallow Creek, east of Ukiah, 12.IV.1998. One sectioned worm (transverse), 2 dissected, 4 in alcohol. 23.IV.1999. One dissected, 5 in alcohol. Spring at highway road cut, along Camas Creek, south of Ukiah, 12.IV.1998. Three sectioned worms (transverse and sagittal), 7 dissected, 8 in alcohol. Denning Spring, on Pearson Creek, 23.IV.1999. Four dissected, 7 in alcohol. All specimens collected by S. Fend.
Size variable (Table 1). External appearance similar to R. yakimorum from the type locality, but with spermathecal pores on or slightly outside the ventral chaetal line (Figure 18a,b). Vascular system and nephridia as described for typical R. yakimorum. Spermathecae paired; ectal bulbs widely separated. Spermathecal bulb nearly spherical; ampulla weakly developed, near cylindrical (Figures 19 and 20); diverticula with 3–5 lobes. Penial bulb nearly spherical, with atrium inserting dorsally. Retracted bulb with
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Figure 17. R. yakimorum variant 1, drawing of penial bulb, from sagittal dissection.
Figure 18. R. yakimorum variant 2, drawing of whole worm, (a) from spring near Ukiah, Oregon, penis everted, (b) from spring at Bear Wallow, Oregon.
prominent, conical penes, length almost equal to width at base (Figures 21 and 22); everted penial bulb obtuse, nearly cylindrical (Figures 18a and 23). Penes directed perpendicularly to body axis both when everted and retracted; male pores slightly lateral on penes (Figure 21). Smaller worms often with atrium coiled in XI.
The material Worms from the three sites differ in size: the median (range) length and width of specimens from the spring at Bear Wallow Creek were 35 (32–50) and 1.9 (1.8– 2.3) mm, compared with 19 (16–26) and 1.0 (0.8–1.4) mm at the spring by Camas Creek. Specimens from Denning Spring were intermediate in size. Nevertheless, form and orientation of reproductive organs is
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Figure 21. R. yakimorum variant 2, from spring near Ukiah, Oregon; transverse section in X. Figure 19. R. yakimorum variant 2 from spring near Ukiah, Oregon; transverse section in VIII.
Figure 20. R. yakimorum variant 2, from spring near Ukiah, Oregon; drawing of spermatheca from sagittal dissection.
consistent, other than a tendency for the atria to coil in smaller specimens. The general arrangement of blood vessels is also consistent. Remarks Rhynchelmis yakimorum shares the large penial sacs or bulbs with R. rostrata and all other members of species Group 1, a character that suggests placement in Sutroa Eisen as defined by Holmquist (1976). As the taxo-
Figure 22. R. yakimorum variant 2, from spring near Ukiah, Oregon; drawing of penial bulb from sagittal dissection.
nomic status of Sutroa is currently unclear, we refer to this group of species as ‘Group 1’ in the present paper. Other characters associating R. yakimorum with Group 1 species include the paired spermathecal diverticula originating at the ectal duct of the spermatheca, the thick bulbs at the spermathecal pores, the atrial morphology and the placement of spermathecal pores anterior to the chaetae in VIII. The yakimorum species complex (including R. yakimorum, R. monsserratus n. sp., R. gustafsoni n.
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Figure 23. R. yakimorum variant 2, from spring near Ukiah, Oregon; drawing of everted penial bulb from sagittal dissection.
sp. and R. utahensis n. sp.) is easily distinguished from congeners by the basic form of the penes and spermathecae; differences between these species are discussed under the various descriptions. The other members of Group 1, R. rostrata and R. gilensis n. sp., have more elongate penes and penial bulbs composed of loose, apparently muscular tissue rather than a compact array of gland-like cells. Both R. rostrata and R. gilensis have elongate, digitiform or irregularly branched spermathecal diverticula, unlike the distinctive lobed diverticula of the yakimorum complex. The diverticula of those species enter the long ectal duct at the base of the ampulla, rather than at the ectal end. R. rostrata also has a very large, sac-like spermathecal ampulla and several diverticula. The atria of R. yakimorum, R. monsserratus, and R. gustafsoni closely resemble those of R. rostrata, and the combination of atrial characters is sufficient to distinguish these species from all congeners, although R. utahensis is similar. The muscle layer is thickened in the ectal (prostate-free) portion of the atrium, the posterior (functional) vas deferens joins near the midpoint, the anterior vas joins the muscle coat near the midpoint and travels to the ental end and the shape is a relatively uniform cylinder (not widened entally). The absence of prostates in the ectal portion is shared with all other Group 1 species as well as with R. orientalis, R. brooksi and R. malevici. Although this character
was illustrated for R. rostrata by Eisen (1892) and Beddard (1895), the subsequent illustration by Cook (1971, pp. 275) implies that the prostates extend to near the ectal end. The epidermal infoldings at the male pores of partially mature worms develop into characteristic, thick-walled penis sacs or bulbs in fully mature individuals. In mature worms in the R. yakimorum complex, the retracted bulbs are compact and globose, with apparently glandular cells surrounding a layer of less-modified cells, interspersed with radial and circular muscle fibers. The possible gland cells occur in indistinct bundles, somewhat resembling prostates and other glands, but they are not strongly granular or dark-staining. The bulbs, common to all members of Group 1, also resemble those of some Lamprodrilus (Lumbriculidae) species (Lamprodrilus bulbosus Isossimov, 1948 and Lamprodrilus pygmaeus Michaelsen, 1901), as well as some Enchytraeidae (e.g. Mesenchytraeus grandis and Mesenchytraeus pedatus, Eisen, 1904). In several other Rhynchelmis species, the male pore is associated with some epidermal thickening and cell modification. Holmquist (1976) described both male and spermathecal pores of R. brooksi as opening on a distinct cushion of cells with associated glands; this cushion is histologically similar to the epidermal infoldings of rostrata and yakimorum, although not invaginated (Figures 76 and 77). The actual male copulatory structures are formed by eversion of the entire penial bulb in R. yakimorum and other species in Group 1. The term ‘penis’ has been questioned for similar structures in the Enchytraeidae (Schmelz & Healy, 1997), as it is improbable that the main part is capable of penetrating the spermathecal opening. Although it also appears that these robust organs do not penetrate the spermathecal duct in R. yakimorum, it is likely that the spermathecal bulb opens to form a sort of copulatory bursa. In preserved material, the transverse slit covering the spermathecal pore is opened to varying degrees. The penial bulbs were not seen in a completely everted state in typical R. yakimorum, yakimorum variant 1 or R. monsserratus, but everted bulbs were seen to be blunt and almost cylindrical in yakimorum variant 2 and R. gustafsoni. In contrast, the copulatory structures of R. rostrata, R. utahensis and R. gilensis have more attenuated tips, and these appear as elongate ‘penes’ when retracted. The apparent penes of each yakimorum variant assume a characteristic shape and orientation (forward, lateral or medial) when retracted. The male pores of the typical yakimorum form (and R.
15
Figure 24. R. monsserratus, Snyder Spring, Idaho; drawings of whole worms (a) fully mature (b) near mature, with extra spermatheca in VII.
Figure 25. R. monsserratus, from Snyder Spring, Idaho; transverse section in VIII.
monsserratus) are likely to be directed posteromedially when everted, due to their slightly posteromedian placement in the retracted bulb. Specimens identified as variant 1 have less distinct penes when the bulbs are retracted than do the fully-mature R. yakimorum from the type locality, and the penes of variant 2 are more distinct. However, this character is subtle and varies with fixation and maturity. It is not clear whether the two forms described here as R. yakimorum variants should be considered geographic variants or additional species within the yakimorum complex. They are less distinctive than the other members of the complex, but can be reliably distinguished by minor differences in the position of spermathecal and male pores as well as the structure of the reproductive organs. Although differences in
alignment of copulatory structures could be argued to be isolating mechanisms indicative of speciation, perfect alignment with spermathecal pores is apparently unnecessary, as shown by variant 1 and the species having a single spermatheca. Position (and number) of reproductive organs have been considered to vary within other species in the Lumbriculidae (Lumbriculus variegatus, for example), although this is usually due to high variability within populations (Cook, 1971). The limited collections of yakimorum variants do not allow us to evaluate geographical consistency, or preclude clinal variation in characters.
16 Etymology: mons (a mountain, mount)+serratus (sawshaped, serrated). The type locality is in the Sawtooth Mountains. Description
Figure 26. R. monsserratus, from Snyder Spring, Idaho; drawing of spermatheca, from sagittal dissection.
Rhynchelmis monsserratus n. sp. Holotype: USNM 186451, a sagittally sectioned specimen. Type locality: Idaho: Custer Co.: Snyder Springs, Salmon River drainage, in watercress roots, 2.VI.1996. Paratypes: USNM 186452-186455: From the type locality, 2.VI.1996. Two sectioned worms (1 transverse, 1 sagittal), 3 dissected, 5 in alcohol. Other material: Idaho: Custer Co.: Cape Horn Marsh, near Banner Summit, 2.VI.1996. Eight sectioned, 4 dissected, 7 in alcohol. Elk Creek, 2.VI.1996. One dissected, 2 in alcohol. Lemhi Co.: Salmon River at Salmon, 13.XI.1998, coll. D.L. Gustafson. Five dissected, 2 in alcohol. Montana: Missoula Co.: Bitterroot River at Chief Looking Glass Park, 5.X.1996, coll. D.L. Gustafson. Two nearly-mature worms (1 sectioned, 1 dissected). Washington: Asotin Co.: Spring along highway west of Fields Spring State Park, 11.IV.1998. Two dissected, 10 in alcohol. Columbia Co.: Spring along North Fork Touchet River below Hompegg Falls, 5.IV.1998. One dissected mature worm, 6 mature or partially mature in alcohol. All collected by S. Fend, unless otherwise noted.
External morphology generally as described for R. yakimorum from the type locality, except the following. Spermathecal opening a single transverse slit (0.2–0.3 mm), anterior to chaetae, nearly median or slightly to one side (Figure 24a,b). Male pores behind chaetae, usually slightly inside chaetal line on X, midpoints separated by about 0.5 mm. Measurements of other characters in Table 1. Spermatheca single in VIII, pore and ectal bulb nearly median, on either left or right side between ventral nerve and ventral muscle band (Figure 25). Morphology of individual spermatheca similar to R. yakimorum from the type locality, but ectal bulb usually somewhat flattened, and wider than long (Figures 25 and 26). Paired male pores directed anterolaterally within penial bulbs, as described for R. yakimorum except that penes not apparent when retracted (Figures 27 and 28). Penial bulbs well separated, slightly flattened dorsoventrally (Figures 28 and 29). Morphology of atria, prostates, vasa deferentia, funnels, testes and ovaries as in R. yakimorum. Postseptal portions of nephridia begin in XIII– XV, nephridia may occur irregularly, paired, single or sometimes absent in posterior segments. Nephridial structure as in R. yakimorum. The material Over 30 sectioned or dissected specimens were used in the description. Almost all were fully mature as indicated by well-developed sperm and eggs, sperm in the spermatheca, and a clitellum. Most of the additional unmounted specimens were cleared to verify the single spermatheca. The unpaired spermathecal pore was slightly lateral to the midline on partially mature specimens. A single individual (of 17 mature worms collected) from Banner Summit had paired spermathecae in VIII. This specimen resembled variant 1 (see below) in that the spermathecal bulbs were closely appressed and the 2 ducts adjacent, not separated by part of the ventral longitudinal muscle. Externally, the single, median opening resembled that of other worms from the collection site. Three specimens, including one of the paratypes, had an additional, unpaired spermatheca in VII, and another had one in IX; the additional spermatheca did not contain sperm.
17
Figure 27. R. monsserratus, from Snyder Spring, Idaho; penial bulb, sagittal section.
Figure 28. R. monsserratus, from Snyder Spring, Idaho; transverse section in X.
Remarks In most respects R. monsserratus closely resembles the other species in the yakimorum complex, although the single, median spermatheca is distinctive enough to have been used as a generic character (see discussion). None of the sectioned or dissected R. monsserratus had a visible penis when the penial bulb was retracted, unlike other members of the yakimorum complex (except R. yakimorum variant 1). The latter character can be affected by the degree of contraction (and consequent penial eversion) resulting from fixation, but was consistent among all collections. The position of the male pores, slightly inside the chaetal
line, does not resemble the strongly median condition of R. gustafsoni. The single median spermatheca of R. monsserratus is shared with two other members of Group 1, R. rostrata and R. gilensis, but not with any other Rhynchelmis. Based on material from 7 sites, R. monsserratus appears distinctive from other species in the R. yakimorum complex, without intermediates. There was high consistency within populations and within the geographic region, the single exception being a possibly aberrant specimen of monsserratus with paired spermathecae (resembling Yukimorum variant 1) that was collected from a population having single spermathecae. Although the occasional loss of repro-
18 Two dissected, 9 in alcohol. Tom’s Creek at mouth, 14.XI.1997. Three dissected, 4 in alcohol. Warm River Spring, 18.X.1997. One dissected, 7 in alcohol. All specimens collected by D.L. Gustafson. Etymology: refers to D.L. Gustafson, who collected the type material. Description
Figure 29. R. monsserratus, from Snyder Spring, Idaho; drawing of penial bulb, from sagittal dissection.
ductive structures on one side has been shown to occur in at least one other lumbriculid (Eclipidrilus ithys Brinkhurst, 1998), our survey of hundreds of specimens of other Rhynchelmis species did not find this aberration in any population. Rhynchelmis gustafsoni Holotype: USNM 186445, a sagittally sectioned specimen. Type locality: Montana: Gallatin Co.: Madison River at Bakers Hole, 12.X.1996. Paratypes: USNM 186446-186450: From the type locality, 12.X.1996. Three sectioned worms (1 sagittal, 2 transverse), 2 dissected, 6 in alcohol. Other material: Montana: Broadwater Co.: Toston big Spring, 11.III.1997. One sectioned worm, 1 dissected, 1 in alcohol. Madison Co.: Duck Creek, 14.III.1997. One in alcohol. Madison River at Madison Camp, 10.V.1997. Two in alcohol. IDAHO: Fremont Co.: Chick Spring, 14.XI.1997. Several in alcohol. Falls River, 4.III.1997. Two sectioned, 2 dissected, 1 whole mount, 6 in alcohol. 13.III.1998. One in alcohol. Henry’s Fork River, various sites, X.1997 to I.1998. Three dissected on slides, several in alcohol. Osborne Springs, 18.X.1997. Two dissected, 10 in alcohol. Robinson Creek at mouth, 18.X.1997.
Single spermathecal opening a transverse slit or oval, median width 0.4 mm (0.24–0.7 mm) in external view; actual pores well inside chaetal line, separated about 0.2 mm (Figure 30a,b). Male pores closely appressed, separated by 0.1–0.2 mm; within a single transverse opening, often with slightly raised margin, median width 0.48 mm in external view. Other external characters as described for R. yakimorum; measurements in Table 1. Vascular system and nephridia as described for R. yakimorum. Nephridia usually begin in XIII; occur irregularly in posterior segments. Spermathecae paired, with closely appressed ectal bulbs inside ventral muscle bands (Figure 31); individual bulb diameter about 300 µm, but basally the paired structure to 550 µm wide, bulbs slightly depressed dorsoventrally. Spermathecal diverticula with 4–7 lobes (Figure 32). Nearly spherical penial bulbs closely appressed, inside ventral muscle bands, individual bulbs 300–500 µm wide (Figure 33); male pores adjacent, directed anteriorly on short penes. Penes fused into a single, blunt structure, about 500 µm long and 500 µm wide when everted; directed forward both when retracted and everted (Figures 33b, 34 and 35). Ventral nerve cord displaced dorsally in VIII and X as it passes over spermathecal and penial bulbs. Remainder of male duct as described for R. yakimorum; measurements in Table 1. The material Most of the sectioned or dissected specimens were fully mature, with sperm in the spermathecae. Several specimens had partially or fully everted penes. In addition to the unmounted mature specimens listed above, many partially mature specimens from the same sites were easily identified by the near median positions of male and spermathecal pores. Variation in the distinguishing characters was minimal, and there was no overlap with other yakimorum complex species or variants. No other Rhynchelmis Group 1 species occurred at sites where R. gustafsoni were collected.
19
Figure 30. R. gustafsoni (a) from Toston Big Spring, Montana (b) penes everted, from Falls River, Idaho.
Figure 31. R. gustafsoni, from Falls River, Idaho, transverse section in VIII.
Remarks Rhynchelmis gustafsoni differs from the other members of the yakimorum complex mainly in the position of the male and spermathecal pores. Male pores are on or near the chaetal line in most other Rhynchelmis, although they are distinctly median to the chaetal line in some of the other species in Group 1, and in a group of Palearctic species associated with R. olchonensis. However, the fused penial bulbs and adjacent male pores of R. gustafsoni are unique within the genus.
Rhynchelmis utahensis n. sp. Holotype: USNM 186456, a dissected worm on slide. Type locality: Utah: Cache Co.: Spring by Logan River at Wood Camp, in moss, 16.X.1997. Paratypes: USNM 186457–186460: From the type locality, 16.X.1997. Two sectioned worms (1 sagittal, 1 transverse), 2 dissected on slides, 8 in alcohol. Other material: Utah: Cache Co.: From the type locality, 16.X.1997. Eight dissected, many in alcohol. 17.IV.1997, coll. R.D. Kathman. Four sectioned,
20
Figure 32. R. gustafsoni, from Madison River, Montana, drawing of spermatheca, from sagittal dissection.
Figure 33. R. gustafsoni, transverse sections in X (a) penial bulbs retracted, from Madison River, Montana (b) penes everted, from Falls River, Idaho.
2 dissected, several immature in alcohol. Rick’s
Spring, near mouth of spring run at Logan River,
21
Figure 34. R. gustafsoni, from Madison River, Montana, retracted penial bulb, sagittal section.
Figure 35. R. gustafsoni, from Henry’s Fork, Idaho: penial bulb, everted, from sagittal dissection.
16.X.1997. Three sectioned, 6 dissected, many in alcohol. Thompson spring, at Logan River, in moss, 16.X.1997. Four dissected, several in alcohol. All collections by S. Fend unless otherwise noted. Etymology: Refers to Utah, the type locality. Description Paired spermathecal pores anterior to ventral chaetae in VIII, paired male pores behind ventral chaetae in X; both sets of pores on or slightly outside chaetal line, separated by 0.5–0.8 mm (Figure 36a). Other
external characters as described for R. yakimorum; measurements in Table 1. Brain, pharynx, body wall musculature, blood vessels and nephridia as described for R. yakimorum. Pharyngeal glands prominent to VI, VII or sometimes VIII. Folded sacs on 8/9 and 9/10 as described for R. yakimorum. Testes in X, occasionally small testes also in IX; ovaries in XI. Sperm sacs extend as far back as XXXIII; egg sacs as far as XXXVI. Spermathecae insert between ventral and ventrolateral muscle bands of body wall (Figure 37). Ba-
22
Figure 36. R. utahensis, (a) drawing of whole worm from type locality, (b) drawing of genital segments, penes everted.
Figure 37. R. utahensis from type locality; transverse section in VIII, spermathecae.
23
Figure 38. R. utahensis spermatheca, transverse section.
sic structure of spermatheca as described for R. yakimorum. Ectal bulb slightly flattened, inner layer of longitudinal muscle covered with thick layer of gland cells in indistinct bundles, interspersed with radial muscles extending to body wall (Figure 38). Base of pyriform ampulla nearly as wide as spermathecal bulb; narrow ental end joins gut (Figures 38 and 39a). Spermathecal bulb rotated so that ectal pore is somewhat lateral and ampulla inserts dorsomedially on bulb. Paired spermathecal diverticula insert anteriorly and posteriorly in wide (to 100 µm), indistinct ectal duct within bulb. Diverticula with 3–10 (or more) irregularly placed, short lobes; total length of diverticula variable, 300–900 µm (Figure 39a,b). Paired penial bulbs insert between ventral and ventrolateral muscle bands of body wall. Bulbs taller than wide; dorsal muscles form distinct retractors connected to dorsal body wall. Male duct enters penial bulb on medial face, sinuous and narrowed at ectal end (Figures 40 and 42). Penes conical and usually slightly longer than width at base, approximately 100 µm long when retracted. Each penis inserts medially within penial sac; tip curved outward, with male duct distinctly offset so that pore is ventral (Figure 40). Length of penial bulbs near 300–400 µm when everted; tip narrowed and curved medially, with offset pore directed dorsally (Figure 36b and 41). Diameter of atrium about 70 µm, with ental portion at most slightly wider than ectal; muscle not strongly thickened in ectal por-
Figure 39. R. utahensis drawings of spermathecae from sagittal dissections (a) from type locality (b) from Rick’s Spring, Utah (diverticula only).
tion, muscle thickness 5–6 µm ectally and 2–3 µm entally (Figure 43a,b). Ental portion of atrium in mature worms longer than ectal portion, with lining cells granular and having indistinct cell walls; ental portion covered with bundles of highly granular prostate cells. Anterior male funnels often indistinct, at most 100 µm wide; 2 specimens with sperm on anterior funnels and in anterior vasa deferentia. Anterior vasa deferentia pass between penial bulbs in X; may be degenerate
24 in X, but only slightly smaller than posterior vas within sperm sacs; join atrial muscle near midpoint and enter atria near ental end. Posterior funnel functional, convoluted but nearly round in transverse section. Posterior vas goes straight up into X, joins atrial muscle near beginning of prostates and may travel in muscle for 1–2 segments before entering atrial lumen. The material A good series of worms at all stages of maturity was available. Two specimens (of more than 30 dissected and sectioned) had functional (although small) anterior funnels and vasa deferentia. A small amount of testis-like material was associated with the sacs on 8/9. There was no overlap in the distinguishing characters with related species, and the R. utahensis collections did not contain other species of Rhynchelmis. Remarks The large penial and spermathecal bulbs, the general structure of the atria and spermathecae, and the anterior placement of the spermathecal pores place R. utahensis in Group 1, and the lobed, paired spermathecal diverticula associate it with the yakimorum complex. The position of the genital pores is similar to R. yakimorum from the type locality, and to yakimorum variant 2. Although the atria and spermathecae of the two species are also quite similar in basic structure, they differ in several details. The large penial bulbs of R. utahensis are taller than wide, often approaching the dorsal body wall. The anterior vas deferens passes between the bulbs, rather than dorsally. The curved, conical penes, the narrow atrium entering the bulb medially and the broad spermathecal ampullae are consistent differences. Histological details of the atrium (rather thin muscle in the ectal portion, granular prostates, and indistinct lining cells) could relate to stage of maturity, but were found in all mated R. utahensis collected at two seasons and consistently differed from all other members of the R. yakimorum complex. The spermathecal diverticula are often larger and more irregularly branched, but this character is less consistent. Form and size of the spermathecal diverticula were quite variable, although, unlike other Group 1 species, additional spermathecae in VII were not seen. The occasional occurrence of testes in IX, with apparently functional funnels, is unusual. Other species of Rhynchelmis, as well as other lumbriculids, have been described as having variable development of the
anterior male ducts. This suggests that these characters, although distinctive, are potentially reversible in phylogenetic analyses. Rhynchelmis gilensis n. sp. Holotype: USNM 186461, a sagittally sectioned specimen. Type locality: New Mexico: Catron Co.: Whitewater Creek near Mogollon, Gila River drainage, 11.VI.1998. Paratypes: USNM 186462–186466: From the type locality, 11.VI.1998. Two sectioned worms (1 sagittal, 1 transverse), 2 dissected, 1 whole mount, 4 in alcohol. Other material: Arizona: Gila Co.: Reynolds Creek at FR 288, 8.IV.1998. One partially mature whole mount, several immature and 1 partially mature in alcohol. New Mexico: Catron Co.: from the type locality, 24.VI.1996. Three sagittally sectioned, 1 dissected. 11.VI.1998. Three sectioned, 1 whole mount, 14 dissected, 11 in alcohol. Gilita Creek at Willow Creek, 22.IV.1996. One whole mount. 12.VI.1998. Two whole mounts, 1 dissected. All collected by S. Fend. Etymology: Refers to the type locality, in the Gila River drainage. Description Small worms; measurements in Table 1. Color of live worms pale, whitish. Up to 91 segments; secondary segmentation beginning in II. Prostomium with proboscis near 0.5 mm, up to 0.9 mm, with slight constrictions. Anterior segments nearly circular in transverse section, segmentation and secondary annulation slightly to moderately developed. Chaetae simple-pointed, sigmoid; nodulus distal to midpoint, ranging from near median to 1/3 of chaetal length from tip; maximum chaetal length near genital segments, slightly shorter posteriorly. Spermatheca single; pore in transverse slit near 0.1 mm wide, between or slightly anterior to chaetae in VIII, medial or slightly to one side of midline (Figure 44a,b). Male pores inside chaetal line and posterior to chaetae in X, separated by about 0.2 mm or joined by a single transverse slit. Female pores small, at 11/12. Clitellum usually from IX–XIV, not always prominent, even in mated worms. Epidermis 10–20 µm thick anteriorly, clitellum variably developed in mature specimens, clitellar epidermis 10–30 µm thick. Longitudinal muscle bands not tapered laterally, do not curl inward; 30–40 µm
25
Figure 40. R. utahensis from type locality; transverse section in X, penial bulbs, retracted.
Figure 41. R. utahensis from Rick’s spring, Utah; transverse section in X, everted penial bulb.
thick anteriorly. Brain medially emarginate, with major ventral nerves joining in II. Pharynx mostly in II–III; dorsal pad not strongly developed. Pharyngeal glands in IV–VI. Distinct, paired cell masses lateral to gut on anterior septum in IX and X. Vascular system with single dorsal and ventral vessels having connections to the gut plexus. Blood glands small, present in some clitellar segments. Preclitellar segments with a single pair of commissural vessels joining the ventral vessel posteriorly. Commissural vessels in X–XII are thickened dorsally, with thinner loops entering the sperm and egg sacs. Segments posterior to XII with a single, anterior pair of lateral blood vessels, unbranched or minimally branched; vessels join gut plexus ventrolaterally or
Figure 42. R. utahensis from type locality; drawing of penial bulb, from sagittal dissection.
laterally as described for R. brooksi (see below). Nephridia usually begin in XIII or behind; may be paired, but not in all segments; absent from many posterior segments. Anterior part of nephridium with small anteseptal funnel and bulbous, granular postseptal portion (Figure 51). A loosely convoluted duct loops dorsally to near the dorsal blood vessel, and may enter adjacent segments. The short, ectal nephridial duct
26 outer muscle layer 2–5 µm thick. Sperm cells lined up in the diverticula. Spermatheca may go to either side, slightly distorting ventral nerve and muscle bands. Paired male pores at tips of elongate, conical penes about 60 µm long by 50 µm wide at base, in bulblike sacs surrounded by thick layer of loosely arranged cells and muscle fibers (Figures 47, 48 and 50). Penial bulbs nearly spherical when retracted, connected to dorsolateral body wall by distinct muscles. Everted penial bulbs form short cylinders terminating in conical penes. Atria strongly convoluted, usually either confined to X or entering XI, but sometimes penetrating into XII (Figure 50a,b). Atrium length 1–1.6 mm, diameter 50–100 µm in ectal part, narrowing slightly in ental part. Prostates multicellular, moderately granular, covering ental 1/3–1/4 of atrium. Atrial muscle layer thin throughout, usually 1–3 µm (Figure 49); atrial lining cells cuboidal, not granular. Two vasa deferentia enter each atrium near the ental end, usually without following it closely within the sperm sacs (Figure 49). Anterior male funnels on 9/10 non-functional, 50–90 µm wide; associated with vas deferens 10–23 µm wide. Functional, posterior male funnels convoluted, 120–220 µm wide; associated with vas deferens 15–36 µm wide. The material
Figure 43. R. utahensis from type locality; transverse sections of atrium. (a) ectal portion, in XI (b) ental portion, with prostates.
may approach the ventral blood vessel; ectal portion (except in the most posterior segments) with a bulbous expansion having a dark-staining (hematoxylin) central area without apparent cell boundaries or nuclei. Nephridopore slightly anterior or medial to the chaetal bundles, conspicuous in external view. Testes paired in X, ovaries paired in XI. Sperm sacs and egg sacs paired, to XXI and XXIX. Female funnels prominent on chaetal line at 11/12. Single spermathecal duct opens into a bulb-like infolding, diameter 70–120 µm, connected to the body wall by diffuse muscles (Figure 45). Ectal duct of spermatheca 80–140 µm long and 45–65 µm wide, joined (anterior and posterior) by 2 club-shaped diverticula 220–390 µm long and 60–120 µm in diameter (Figure 46). Short ental duct widens into distinct ampulla 80– 110 µm wide before connecting to gut. Spermathecal ducts and diverticula with cuboidal lining cells, and
The sectioned worms and most of the dissected and whole-mounted worms from the type locality were fully mature, and 4 additional specimens from Gilita Creek were also mature. The 2 partially mature specimens from Arizona had typical body size, vascular system, and arrangement of genital pores, and all specimens from that site had the distinctive ampullae on the ectal ducts of the nephridia. There was no variation in the number, placement or general form of the reproductive organs, although more than half of the mature worms from the type locality had parasites in the sperm sacs. Some specimens had sperm sacs projecting anteriorly into IX. One specimen had a nephridium in VIII (opposite the spermatheca) and another in IX; all mature and immature specimens had nephridia with ectal ampullae. Details of the vascular system were difficult to see in most specimens; observations are mostly based on transverse sections. Remarks Rhynchelmis gilensis is close to Rhynchelmis rostrata, and can be associated with Group 1 on the basis of the single spermatheca in the anterior part of VIII, long penes within penial bulbs, nonfunctional anterior
27
Figure 44. Rhynchelmis gilensis, drawings of whole worms from type locality (a) penes retracted (b) penes everted.
Figure 45. Rhynchelmis gilensis, from type locality; transverse section in VIII.
vasa deferentia, the bulb-like thickening at the spermathecal pore, diverticula originating at the ectal duct of the spermatheca, and multicellular prostates absent from the ectal ends of the atria. It differs from R. rostrata and other Group 1 species in its smaller size, reduced vascular system, small spermathecal ampulla, Two club-shaped spermathecal diverticula, vasa deferentia joining the relatively short atria at or near ental end, the lack of a thick muscle layer in the ectal portion of the atria and the unusual nephridia. Several characters suggest a simplification of R. rostrata morphology, relating to the small size of these worms. Observations of mature individuals from several populations of R. rostrata suggest a reduction in number of segments, length of atrium and sperm and egg sacs in smaller individuals (unpub. data).
However, the morphology of the spermatheca appears consistent in each species, and the ectal end of the nephridial duct was never expanded in R. rostrata. The spermathecal diverticula were never lobed, unlike the R. yakimorum complex. The restriction of prostates to the ental 1/3 or less of the R. gilensis atrium is reminiscent of R. brooksi, but the middle portion is not thickened and glandular, as in that species. The presence of large anterior sperm sacs in IX is unusual in the genus, but was not consistent. The pale color of living specimens contrasts with most other North American species, which are reddish-brown to pinkish, presumably due to extensive development of the blood-vascular system. This character, and sometimes a reduced circulatory system, have also been noted for European species liv-
28
Figure 46. Rhynchelmis gilensis, from type locality; drawing of spermatheca, reconstructed from sagittal sections.
ing in rhithral habitats (e.g. R. vejdovskyi Hrab˘e & Cernosvitov, 1925; R. granuensis Hrab˘e, 1954; and R. vagensis Hrab˘e, 1961). The other small Nearctic species, R. brooksi and R. saxosa, also have a reduced circulatory system (see below). Although nephridia are not always described in detail, the basic structure (cf. Figure 59) appears consistent within the genus except for the present species and R. vejdovskyi. Hrab˘e & Cernosvitov (1925) illustrated and described a ‘grande ampoule piriforme’ at the nephridopore of R. vejdovskyi, similar to the enlarged ectal duct of R. gilensis. Ectal ampullae are referred to as ‘urinary bladders’ in other oligochaetes (Chekanovskaya, 1962).
Figure 47. Rhynchelmis gilensis, from type locality; transverse section in X.
Rhynchelmis rostrata (Eisen, 1888) =Sutroa rostrata Eisen, 1888; Sutroa alpestris Eisen, 1892 Material examined: California: San Francisco Co.: Undetermined location, possibly Mountain Lake, coll. G. Eisen, BMNH 1904.10.20.1012–1016, 1904.10.5.1131–5. Two partly mature, sectioned worms (as S. rostrata types). 1904.10.20.1005–6. One mature, sectioned worm (as S. alpestris). Several immature worms in alcohol, labelled S. rostrata types. Mountain Lake inlet, San Francisco, 23.VI.1996. Three sectioned, 1 dissected, 1 in alcohol. Lobos Creek, San Francisco, 12.VI.1997. Two dissected, 4 in alcohol. Placer Co.: Truckee River above Truckee, 18.XI.1995. Eight sectioned, 10 dissected, 9 in alcohol. San Mateo Co.: small creek north of Half Moon Bay, 21.IX.1996. One dissected. 26.IV.1998. One dis-
Figure 48. Rhynchelmis gilensis, from type locality; sagittal section in X.
sected, 1 in alcohol. Shasta Co.: Sacramento River at Redding, 21.X.1996. One sectioned, 2 dissected, 7 in alcohol. 18.I.1999. Four in alcohol. Sacramento River between Red Bluff and Redding, 21.X.1996. Six in alcohol. Siskiyou Co.: Christmas Tree Ridge, near Yreka, 17.X.1989, coll. W.M. Fender. One dissected. Idaho: Batista Springs, Bannock Co. 9.IX.1995, coll. W. Foster. Three sectioned, 3 dissected, 6 in alcohol.
29
Figure 49. Rhynchelmis gilensis, from type locality; sagittal section in XI, atrium.
Nevada: Douglas Co.: small creek at Zephyr Cove, Lake Tahoe, 6.XI.1996. Ten dissected, partially mature worms. Oregon: Deschutes Co.: Deschutes River, near Bend, 22.X.1995. Six sectioned, 5 dissected, 5 in alcohol. Wasco Co.: Deschutes River near South Junction, 26.X.1995. Two sectioned, 8 dissected, 20 in alcohol. Utah: Cache Co.: Little Bear River at Paradise, 16.IV.1999. Four dissected, 15 in alcohol. Wasatch Co.: Cascade Springs, 17.X.1997. Two dissected, 3 in alcohol. All collected by S. Fend unless otherwise noted. Supplementary description Size variable; measurements in Table 1. Color of living worms dark reddish to pinkish; preserved worms pale, unpigmented. Chaetae varying in size and curvature, but with distal nodulus and similar form and size in dorsal and ventral bundles (Figure 53a– c). Spermathecal opening single, slightly anterior to chaetae, near median or slightly to one side (Figure 52a,b). Male pores behind chaetae in X, inside the chaetal line. Female pores indistinct at 11/12, on chaetal line. Vascular system generally as described for R. yakimorum. Specimens from all sites with ventral blood vessel forking in VII, both forks connected to the dorsal vessel by strongly convoluted commissural vessels in II–VII. Two pairs of variably branched lateral vessels in VIII and posterior segments; most branches end in lateral and ventral part of body wall. One branch of each posterior pair connects directly to ventral vessel up to XII, with loop into sperm/egg sac
in X–XII. Anterior pair of lateral vessels with ventrolateral branch to the gut plexus posterior to about XIII, and posterior pair with lateral branch to gut posterior to about XL. Branching of lateral vessels varies within populations. In some specimens the anterior pair with long branches, and the posterior with only short lobes in the dorsal region. In other worms (or more posterior segments of the same worm), both lateral vessels with many long branches in addition to short lobes. One living specimen with both short dorsolateral and long terminal branches on one side, and unbranched vessels on the other. Longitudinal muscle bands poorly defined; not strongly tapered or curled inwards at lateral margins. Nephridia usually paired in segments posterior to about XII, morphology as described for R. yakimorum (Figure 59). Paired, sac-forming cell masses lateral to gut on anterior septum in IX and X, small or absent in VIII. Sacs associated with septal sphincter and ventro-posterior muscles, without ectal duct; 1 or 2 spermathecal diverticula may project into sacs in IX. Similar sacs may project forward from the posterior ventral aspects of VIII and IX. All mature specimens with a single spermatheca in VIII. Spermatheca to left or right of ventral nerve and gut; ental part of ampulla joined dorsally or laterally to the gut. Ectal pore within variably developed, glandular bulb, similar to that described for R. yakimorum (Figures 54 and 55a). Spermathecal ampulla large (Table 1), irregularly globose; sperm loosely packed in the ampulla (Figure 54). Usually 6 or 7 (as few as 4 or as many as 10) digitiform or branched-digitiform diverticula join the elongate ectal duct below the ampulla; size of diverticula variable, but width less than 1/10 length (Figure 55a,b). Diverticula with sperm heads lined up along the wall or between cells; both diverticula and ampulla with thin muscle layer surrounding inner layer of more or less cuboidal lining cells. In many specimens, 1 or 2 spermathecal diverticula with a single, usually distal fork. Additional unpaired spermathecae in VII in occasional specimens from several sites. Partially mature spermatheca with short diverticula and narrow ampulla. Atria may extend past XX; ectal portion with thick muscle layer (near 10 µm), without prostates; ental portion as long or longer than ectal, with prostates, and with thinner muscle layer. Atrial lining cells cuboidal, not obviously glandular. Multicellular prostate glands closely packed and difficult to distinguish in fully mature worms (Figure 56), but more loosely packed when partially mature. Anterior (nonfunctional) vasa deferentia usually less than 30 µm
30
Figure 50. Rhynchelmis gilensis, from type locality; drawings of atria, from sagittal dissections, (a) extended, with penis everted (b) folded.
Figure 51. Rhynchelmis gilensis, from type locality; drawing of nephridium from whole mount.
wide, enter atrial muscle coat near midpoint, in XII or XIII. Posterior vasa deferentia usually 30–40 µm wide, joining atria soon after beginning of prostates, usually entering lumen after travelling 1–2 segments under the muscle coat. Eversible, bulb-like penis sacs
not obviously glandular, composed of loosely-packed cells interspersed with muscle fibers; penes apparently formed from loosely-packed muscle surrounding the male duct (Figures 57 and 58). Muscle fibers continuous with ventral body wall, coalesce into distinct
31
Figure 52. Rhynchelmis rostrata, drawing of whole worm (a) from near type locality (b) from Deschutes River, Oregon, penes everted.
Figure 53. Rhynchelmis rostrata, chaetae: (a) typical, Deschutes River, Oregon (b) typical, Batista Springs, Idaho (c) typical, 3 sites from the Sierra Nevada, California, near Lake Tahoe (d) variant 2; dorsal and ventral chaetae from IV, XV and a posterior segment of a single worm; Lake Tahoe, California or Nevada.
muscle bands extending to dorsal body wall. Penial bulbs basally contiguous and directed anterolaterally when everted; fusiform, to 600 µm long (Figures 52b and 58). Retracted penes elongate, conical (length about the same as width), medially directed, entering common ectal opening.
Eight sectioned, 11 dissected, 4 in alcohol. Sierra Co.: Big Spring, near Bassets, 6.VIII.1996. Four sectioned, 8 dissected, few partly-mature in alcohol. All collected by S. Fend.
R. rostrata variant 1
Measurements similar to typical R. rostrata (Table 1). Blood vessels and most other characters as described for typical R. rostrata. Most specimens from the listed sites have several spermathecal diverticula with basal
Material examined: California: Nevada Co.: small spring near west shore of Donner Lake, 30.V.1996.
Description
32 and/or distal forks, often with more than 1 fork per diverticulum (Figure 55c). A single specimen from the spring near Donner Lake with spermatheca and atrium shifted forward 1 segment (to VII and IX); all others with normal placement in VIII and X. R. rostrata variant 2 Material examined: California/Nevada: Lake Tahoe, coll. T. Frantz, USNM 32997. One sectioned and 2 dissected worms. Description Ventral chaetae longer and slightly thinner than dorsals, with a distinctly proximal nodulus; dorsal chaetae with nodulus slightly to distinctly distal, as in typical R. rostrata (Figure 53d). Spermathecae and male ducts as described for typical R. rostrata, except atrial muscle thinner (near 5 µm in ectal portion). Spermathecal diverticula unbranched (similar to Figure 55a). The material All of the R. rostrata collections included some fully mature, mated specimens except the creek at Zephyr Cove, and the possible type specimens labelled as R. rostrata by Eisen. Many of the unmounted specimens were cleared to verify the basic structure of the reproductive and circulatory systems. In addition to the listed specimens, most collections contained partially mature worms, and all of these specimens had a single spermathecal pore in VIII. In general, collections were dominated by immature and partially mature worms. The new collections from California include the type localities for R. rostrata and S. alpestris, and one other California locality given by Brinkhurst & Cook (1966). Two specimens from Yellowstone Park, Wyoming (USNM 26280), attributed to this species by Brinkhurst & Cook (1966), were immature and could not be identified. The only material collected by Eisen included several immature or partially mature worms from at or near the type locality of R. rostrata, and a single mature, sectioned worm labeled Sutroa alpestris, in good condition, but with no collection data. The latter specimen appears to be the one illustrated by Beddard (1895). As the accession date on this worm is the same as the others, and it resembles R. rostrata collected by us from the type locality, it may be from that site. The material described here as R. rostrata variant 2 was listed as a ‘hypotype’ of R. rostrata, and apparently illustrated
Figure 54. Rhynchelmis rostrata, from Truckee River, California; sagittal section in VIII; spermathecal ampulla and bases of diverticula.
by Brinkhurst & Cook (1966). Although the specimens were fully mature, the description here is limited because the two dissections were incomplete, and the mounting medium of the sectioned worm had greatly deteriorated. Attempts to collect additional specimens (Bob Richards, University of California, Davis) were unsuccessful. Remarks The original description (Eisen, 1888), subsequently emended (Eisen, 1892), is detailed, but contains several apparent errors, possibly due to the author’s use of dissections rather than serial sections. A redescription by Beddard (1895) corrects many of these problems, but his observations on reproductive structures may be based on a single sectioned worm, labelled Sutroa alpestris, from an uncertain locality. Some of the material used in these descriptions appears not to have been fully mature (as determined by welldeveloped sperm and eggs, and sperm present in the spermatheca). All observed specimens, from many localities throughout the wide distribution, had a single, nearmedian spermatheca in VIII, a character previously confirmed by Brinkhurst & Cook (1966) for specimens from several other locations. Additional un-
33
Figure 55. Rhynchelmis rostrata, sagittal drawing of mature spermatheca, from dissections (a) typical, from San Francisco, California (b) typical, with forked diverticulum; from Sacramento River, California (c) variant 1; from Donner Lake, California, 2 diverticula from the same spermatheca.
paired spermathecae in VII appear to be a regular, although infrequent, occurrence. However, none of the observed R. rostrata populations had more than one spermatheca in VIII, even at early stages of development. In all Rhynchelmis species with this character (R. rostrata, R. monsserratus and R. gilensis) the initial epidermal infolding is slightly to one side, and the eventual median appearance of the pore is the result of much enlargement. Variation in mature spermathecal form may occur among populations of R. rostrata. Mature R. rostrata had spermathecal diverticula that were at least 10 times longer than wide, inserting below a greatly expanded ampulla. Specimens listed as ‘R. rostrata variant 1’, from the type locality of S. alpestris (Donner Lake) and one other Sierra Nevada site, generally had longer and more highly branched diverticula, a character illustrated but not discussed in the original description of S. alpestris (Eisen, 1892). The actual number of spermathecal diverticula was hard to determine in worms from these two populations, due to extensive branching near the base. These worms are considered a possible variant here, but within-population variation was high. Another character used in that paper to distinguish S. alpestris from R. rostrata, spermathecae in VII instead of VIII, was only seen in a single individual. The shape of the spermatheca also differed from Eisen’s illustrations. Although the spermathecae are quite distinctive in fully mature worms, those of R. rostrata and R. yakimorum may be similar at early developmental stages. In partly mature R. rostrata and yakimorum, the spermathecal diverticula are very short and the ampulla is long and cylindrical, even after formation of the gut connection. Male pores were equipped with distinct penes, and the form (both within the sac and everted) generally ageeed with the original description and illustrations of S. alpestris (Eisen, 1892), although size varied considerably. As in other Group 1 species, the entire penial bulb everts to form the copulatory organ, so the size of the ‘penis’ within the retracted sac probably varies with contraction. We did not observe the associated glands illustrated by Eisen, and the surrounding sac was a loosely formed, muscular structure with possible gland cells poorly defined. Our material agrees with Beddard’s (1895) corrections of the original description regarding the position of the male funnels and the abrupt ending of the posterior vas deferens midway along the atrium. However, the posterior vas deferens was rarely as thick as his illustration, which was apparently based on the BMNH specimen labelled S. alpestris. As the two vasa
34
Figure 56. Rhynchelmis rostrata, from Deschutes River, Oregon, sagittal section; atrium with prostates.
Figure 57. Rhynchelmis rostrata, from San Francisco, California (type locality); transverse section showing retracted penial bulb.
were often similar in size in other specimens, it was not always possible to tell which entered the atrium first. Although this and other details of atrial structure generally show great similarity to R. yakimorum, all populations of R. rostrata had very closely packed prostates that were difficult to distinguish in fully mature worms, while most other species had somewhat smaller, easily distinguished cell bundles.
The prominent cell masses on 8/9, 9/10 and sometimes 7/8 were described by Eisen (1888) for R. rostrata and S. alpestris as ‘albumen glands’. Eisen described and illustrated these organs with an ectal pore and duct, which we did not observe in any of our R. rostrata specimens, or in any of the other species examined. Beddard (1895) also failed to find ducts or obviously glandular cells in his redescription of
35
Figure 58. Rhynchelmis rostrata, from spring near Donner Lake, California; sagittal section showing everted penial bulb.
Figure 59. Rhynchelmis rostrata from Sacramento River, California; drawing of nephridium, reconstructed from sections.
S. alpestris, which was based on Eisen’s material. Structurally, these organs resemble sperm sacs, and are associated with a similar septal musculature. The cells do not appear to be particularly modified (granular or dark-staining) from normal epithelium. Beddard (1895) described these structures as sac-like, and several of our R. rostrata specimens from various sites had one or two spermathecal diverticula penetrating 8/9 into IX within the sacs. In most R. alaskana and R. saxosa (see below) and also in the Asian R. orientalis
(Yamaguchi, 1936), the spermathecae penetrate 8/9 or farther within sacs. Similar structures were described as rudimentary sperm sacs for the European R. vejdovskyi and R. limosella by Hrab˘e & Cernosvitov (1925). In view of their presence in many related taxa, it is likely that these are rudimentary structures, derived from spermathecal sacs in an orientalis-like precursor. However, their morphological similarity to sperm sacs suggests that those in X could be con-
36 sidered vestigial sperm sacs, as sperm sacs are present in X in at least some species with testes in IX. The vascular system has been described in varying detail in Rhynchelmis species descriptions, and some apparent differences may be related to general difficulty of observation, or variation within and among individuals in a population. Descriptions by Eisen (1888), Smith & Dickey (1918), Altman (1936) and Yamaguchi (1936) agree overall, but differ in details. Our observations of the R. yakimorum complex, as well as R. rostrata, R. elrodi, R. glandula and R. alaskana, are all closest to the description of R. elrodi by Smith & Dickey (1918). Despite the variations in the vascular systems of European species considered by Hrab˘e (1961) to be taxonomically useful, our observations suggest little consistent variation among most Nearctic species, including members of both Group 1 and Group 2. The exceptions, R. gilensis, R. saxosa and R. brooksi, all appear to show a decrease in extent and complexity of lateral vessels rather than basic differences in organization. To some extent, this corresponds to the generally smaller body size of those species. A connection between both pairs of lateral vessels and the gut plexus in posterior segments, noted for the anterior pair in R. elrodi by Smith & Dickey (1918), appears to be present in all but the latter 3 species. Observations of live R. rostrata from the Sacramento River and from San Francisco showed considerable variability in degree of branching of the lateral vessels. Eisen (1892) used some differences in the vascular system to distinguish R. rostrata and S. alpestris. Although most of our observations are limited to preserved material, we were able to determine that all Nearctic Rhynchelmis species, including material from the alpestris type locality, had the ventral vessel dividing in VII or at 6/7, rather than in V as described for alpestris. Sectioned material, including the specimen apparently used in Beddard’s (1895) redescription of S. alpestris showed no indication of the anterior ventral vessels being joined by transverse vessels as originally described. Connections between the lateral and ventral vessels, also used by Eisen to distinguish S. alpestris, appeared to be the general condition for the posterior pair of lateral vessels up to about XII in most Nearctic species, but we did not observe this in more posterior segments. Because of discrepancies between Eisen’s and our observations of these and other characters used to separate R. rostrata and S. alpestris, we accept the decision by Brinkhurst & Cook (1966) to combine these species.
Although not as important as in some oligochaete families, chaetal characters are used to distinguish a few lumbriculid taxa. However, with the exception of R. brooksi, chaetae appear to be of very general form in most of the North American Rhynchelmis: simple-pointed and moderately to strongly sigmoid, with the nodulus distal to the midpoint. Chaetal size and curvature vary among and within R. rostrata populations (Figure 53), which suggests these are of little taxonomic value. The ventral chaetae in all of the 3 specimens from Lake Tahoe are an interesting exception. These were morphologically different from the ‘normal’ dorsal chaetae in the same specimens, and their greater length and proximal nodulus bears some resemblance to dorsal chaetae of some groundwater lumbriculids (Trichodrilus capilliformis Giani & Rodriguez, 1994; Stylodrilus wahkeensis Rodriguez & Coates, 1996). Hrab˘e (1931) used elongate ventral chaetae to distinguish a subspecies of Lamprodrilus pygmaeus. As material is limited, and other characters are similar to those of R. rostrata, we hesitate to designate a separate taxon. Typical R. rostrata were found in an inlet to the lake, and also in the Truckee River downstream of the lake. Collection data for the Tahoe specimens are not detailed, but it is possible that these chaetae are modifications for an unusual benthic lake habitat. Distribution and ecology of Group 1 species The different species and variants within the R. yakimorum complex appear to have limited ranges, with little overlap (Figure 79). Most collections are from drainages of tributaries to the Columbia River, except for R. yakimorum variant 1, R. utahensis, and some populations of R. gustafsoni (see below). Mature specimens of the typical form of R. yakimorum have only been collected in the Yakima River mainstem and 2 tributaries, in eastern Washington State, at elevations between 400 and 800 m. No other Rhynchelmis species were found at these sites. This portion of the river is a 6th order stream with gravel and cobble bottom. Despite intensive agricultural water use, the water quality is generally high and summer temperature usually less than 20 ◦ C (Rinella et al., 1992). R. yakimorum densities were highest in stable riffles, but they were not found in fine sediments near the bank. Seasonal development of the population appears highly synchronous, with mature worms occurring in winter and only partially mature worms as late as October. Other dominant oligochaetes in the same habitats included Stylodrilus heringianus,
37 Nais behningi and an undescribed Mesenchytraeus. The typical form has not been reported elsewhere in Washington despite widespread collecting by Altman (1936) and Spencer & Wisseman (1993) in the western part of the state. Partially mature Rhynchelmis from the lower Yakima River Basin and from a nearby site on the Columbia River more closely resembled R. elrodi in the form and placement of male and spermathecal pores. The California specimens of R. yakimorum variant 1 were only found in two small springs along the Klamath River; some in a patch of Equisetum and some under moss-covered rocks. Most individuals were immature or partially mature on the April and December collection dates. Associated oligochaetes were mostly enchytraeids, Fridericia and Mesenchytraeus spp. The limited distributional information suggests that variant 1 has a wide range, but this may be due to imprecise identifications caused by limited material and the intermediate character states. The Oregon specimen was a single, poorly-preserved individual collected along with a large series of R. rostrata, and the Idaho worms (collected in August) were too immature for positive identification. Rhynchelmis yakimorum variant 2 was collected in submerged moss and macrophyte roots in three small, cold springs within a 20 km radius in the Blue Mountains of eastern Oregon, at elevations near 1000 m. The springs are on tributaries to the John Day River and the Umatilla River, both of which are tributaries to the Columbia River. A high proportion of specimens was at least partially mature on the two April collection dates. Although worms varied greatly in size among the sites, the habitats did not appear greatly different. Associated oligochaetes included Mesenchytraeus sp. and Nais bicuspidalis. Mature specimens of R. monsserratus have been collected in the mainstem of the Salmon River, at three sites within the Salmon River drainage at the northern end of the Sawtooth Mountains in Idaho, at one site in the Bitterroot River, Montana and in two cold springs in southeastern Washington. The Washington sites are in the drainages of tributaries to the Snake and Columbia Rivers. Sites included unvegetated, silty patches in a snowmelt meadow (elevation 2200 m), a rapid, gravel bottom stream, large rivers, vegetated spring runs, and high gradient mossy springs. This species appears to mature at various times of year, depending on the population. Nearly half of the larger individuals were mature in November in the Salmon River, and in early June at the Sawtooth Mountain collection sites, but most were only partially mature
in April at the Washington sites. Associated oligochaetes at these sites included Mesenchytraeus spp. and Rhyacodrilus coccineus. Rhynchelmis gustafsoni has the easternmost distribution. It was collected at several river and spring sites in two drainages: in the Madison River, which is part of the Missouri River drainage in southwestern Montana, and from the Falls and Henry’s Fork Rivers in the upper Snake River drainage in eastern Idaho. Highest densities generally occurred in springs, and most stream collections are from relatively unimpaired upper reaches, at elevations between 1500 and 2000 m (D.L. Gustafson, Montana State University, pers. comm.). It occurred with R. elrodi at one spring along the Madison River, much farther downstream than other variant 2 collections. It is likely that the spring habitat provided a refuge from degraded conditions in the lower portion of the river (D. L. Gustafson, pers. comm.). Rhynchelmis gustafsoni was the only member of the genus at all other sites where it occurred. Mature worms were collected from October through May at the various sites. Specimens of R. utahensis at all stages of maturity were collected from 3 cold springs along a 10 km stretch of the Logan River, elevation near 2000 m, on a single date in autumn. A few mature worms were also collected in summer from one of the sites, but only immature worms were seen during a subsquent April visit. Rhynchelmis utahensis densities were highest near the spring outflows, and they were not found at the spring sources or in the receiving river. Although the species appears to disperse along the river, the springs appear to be an important refuge from scouring in the strongly erosional, main-channel habitat. Most specimens were collected in moss, but individuals collected under rocks in riffle habitat were much larger, with more extensive development of reproductive structures. High densities of Mesenchytraeus sp. were also found at one of the sites. The Logan River is in the watershed of Great Salt Lake, an internal basin, which suggests isolation from populations of closely related species to the north. The known distribution of R. gilensis is far to the south of the known ranges of related species. Specimens were collected in three small headwater streams in coniferous forest, within the Gila River drainage in New Mexico and Arizona, at elevations of 2000– 2500 m (Figure 79). At the type locality they were common near the surface of submerged gravel bars, possibly indicating hyporheic habitat; high densities of Rhyacodrilus coccineus also occurred in this habitat. At the other sites they occurred sparsely, in
38 patches of gravel in cobble riffles; associated oligochaetes included Rhyacodrilus, various enchytraeids, and an undescribed Trichodrilus. Rhynchelmis gilensis appeared to be absent from several other streams in the region, many of which had large amounts of fine sediment mixed with the coarser material in the riffle substratum. The lower portion of the Gila River is warm, sandy, and intermittent, presumably restricting this species to headwater sites in the drainage. Most verified records of Rhynchelmis rostrata are from Pacific coastal states, the main exception being three collections from eastern Idaho and Utah (Figure 79). The only other mid-continent material we obtained (USNM 26280, Yellowstone National Park, Wyoming) proved to be too immature to identify, and were likely another species. Collection efforts in intervening regions have not produced any material attributable to this species. A possible explanation for this apparent disjunction is the widespread introduction of salmonid fishes, including the Pacific coastal Onchorhynchus mykiss. One of the Utah collection sites was below an old fish hatchery. Most worms attributed to this species were morphologically similar, although possible variants noted in the description occur in close proximity in the Sierra Nevada in eastern California. Although elevation at R. rostrata collection sites ranged from sea level to above 2000 m, all sites appeared to be cool-water habitats, based on ambient temperature and associated fauna. Habitats included mid-size rivers, isolated coastal streams, small springs and lakes. River habitats were typically lower rhithral, with apparently stable cobble to gravel bottom, often with mosses or sparse vascular macrophytes, and the species was usually sparse or absent from marginal areas having finer sediment. However, R. rostrata was sometimes abundant in silty or sandy sediment in springs and small streams, and was often associated with aquatic vegetation. The specimens listed as variant 1 occurred in 2 small, montane springs in the Sierra Nevada. The unusual specimens from Lake Tahoe (variant 2) are the only examples we have seen from lake habitats; the original report (Frantz & Cordone, 1996) did not provide specific habitat data (littoral vs. profundal) for this species. Specimens of R. rostrata from most sites had a wide range of maturity on the collection date. In contrast, populations from some higher elevation sites (springs near Donner Lake and Zephyr Cove) appeared more synchronous, with most of the large specimens at a similar stage of maturity on a given
collection date. GROUP 2: Spermathecal pores paired, simple, posterior to the ventral chaetae in VIII; ental duct to gut may be absent; ectal ducts thick, without diverticula. Male ducts without penial bulbs; atria usually with prostates in ectal part; anterior vasa deferentia absent in Nearctic species; vasa deferentia enter atrial muscle near ectal end. Rhynchelmis elrodi Smith & Dickey, 1918 Material examined: Idaho: Fremont Co.: Falls River at Porcupine Branch, 13.III.1998. One dissected, 4 in alcohol. Teton River at Hog Hollow Branch, 18.IV.1998. Two dissected, 16 in alcohol. Madison Co.: North Fork Teton River at US 20, 24.I.1998. One dissected, 2 in alcohol. South Fork Teton River at US 20, 25.I.1998. One dissected, 3 in alcohol. Teton Co.: Trail Creek at Mike Harris Camp, 14.III.1998. One dissected. Warm Creek at Drake Creek, 14.III.1998. One dissected. Montana: Beaverhead Co.: Big Spring below Clark Canyon Dam, 3.XI.1994. Two sectioned, 2 dissected, 5 in alcohol. Broadwater Co.: Missouri River at Townsend, 9. XI.1991. One dissected. Toston Big Spring, 30.XI.1995. Two sectioned, 2 dissected, 8 in alcohol. Cascade Co.: Giant Spring, near Missouri
Figure 60. Rhynchelmis elrodi, from spring near Coram, Montana; sagittal section; spermatheca.
39
Figure 61. Rhynchelmis elrodi, from spring near Coram, Montana; sagittal section; ectal end of atrium.
River, 22.XI.1996, coll. R. D. Kathman. Two dissected. Deerlodge Co.: Big Hole River at Sportsman Camp, 4.X.1996. One sectioned, 3 dissected. Grassy Point Spring, 16.II.1997. One dissected. Flathead Co.: Flathead Lake, Yellow Bay, 11.VII.1914, coll. M. J. Elrod and A. G. Vestal, USNM 25502. Paratype, 1 sectioned. Spring near Coram, 16.VI.1996, coll. S. Fend. Two mature and 2 immature sectioned. Creston area spring, 6.I.1994, 2 dissected. Granite Co.: Ditch below Gillies Branch, 21.VI.1997. One dissected. Spring Creek on Rock Creek Road, 5.X.1996. Two dissected. Lake Co.: Swan River at FR 966, 11.IV.1997. Two dissected, 3 in alcohol. Lewis and Clark Co.: Missouri River at Craig, 28.III.1998. Two dissected, 1 whole mount, 19 in alcohol. Missouri River below Holter Dam, 10.XI.1996. One dissected. Lincoln Co.: Lake Creek at Cutoff Branch, 10.IV.1997. One dissected. Missoula Co.: Blackfoot River at Marco Flat, 14.IX.1996. Two dissected, 2 in alcohol. Clearwater River below Seely Lake, 12.IV.1997. One dissected, 2 in alcohol. Owl Creek, 12.IV.1997. One dissected, 2 in alcohol. Petty Creek, 30.VIII.1998. One dissected, 1 in alcohol. Powell Co.: Cottonwood Creek at MT 200, 22.III.1997. One dissected, 3 in alcohol. Kleinschmidt Spring Creek at mouth, 21.IV.1997. One dissected. Racetrack Creek, 18.II.1997. One sectioned, 1 in alcohol. Ravalli Co.: East Fork Bitterroot River. Two
Figure 62. Rhynchelmis elrodi, transverse sections of atria (a) normal, from Racetrack Creek, Montana (b) thick muscle, an unmated worm from Cottonwood Creek, Montana.
dissected, 1 in alcohol. North Burnt Fork Creek at East Road, 10.III.1997. One dissected, 1 in alcohol. Utah: Cache Co: Little Bear River at Paradise, 16.IV.1999, coll. S. Fend. One dissected, 2 in alcohol. Wyoming: Lincoln Co.: Snake River above Palisades Reservoir, 20.III.1999. One dissected, 1 in alcohol. All speci-
40 mens collected by D. L. Gustafson unless otherwise noted. Supplemental description Size of specimens from several sites given in Table 1. Male and spermathecal pores near posterior margin of segments X and VIII, on chaetal line between muscle bands. Sacs filled with cells on septa in IX and X, as described for R. yakimorum. Midventral glands absent from anterior segments in all stages of development. Nephridial tubules with long dorsal and medial loops and simple ectal ducts as described for R. yakimorum. Vascular system well developed, diameter of blood vessels in preserved specimens usually greater than in the other Nearctic species (except R. glandula). Morphology and arrangement of blood vessels as described by Smith & Dickey (1918); in addition, posterior to about XL both lateral vessel pairs with branch to the gut plexus, the anterior inserting ventrolaterally and the posterior inserting laterally. Spermathecal ducts thickened entally, diameter to 140 µm; lining cells columnar, with nuclei arranged peripherally (Figure 60). Spermathecal pores without ectal pad or bulb, glands indistinct or absent. Spermathecal ampullae usually widened basally when fully mature. Epidermis not thickened around male pore; pore surrounded by a few small, usually indistinct glands (Figure 61). Atria usually somewhat distended near ental end; with prostates from near ectal end (usually in X or XI) to ental end (Figure 61). Muscle thickness nearly uniform in atrium, but varies considerably among individuals or populations. Partly-mature specimens from some sites with thick atrial muscle layer 10–20 µm; all fully-mature worms with atrial muscle less than 10 µm, to as little as 3 µm thick (Figure 62a,b). Eversible penis sacs muscular, without incorporated gland cells; may be weakly defined. Penes distinct when retracted; simple extensions of atrial duct near 50–100 µm long (Figure 61). Length of entire male copulatory structure to near 200 µm when everted, resembling Figure 65. No anterior vasa deferentia in any population observed. Posterior vasa usually join atrial muscle layer in X, but some specimens from the Wyoming site and one site on the Teton River, Idaho with beginning of prostates and junction of vasa deferentia and atria in XI or XII. The material The paratype material was in fairly good condition, but much faded. Worms from new collections, used in external measurements, had well-developed male
and spermathecal pores, although many were only partially mature. Nevertheless, most of the listed collections contained at least one or two fully-mature specimens, with developed clitellum and sperm in the spermathecae. Many specimens had everted penes, even when only partially mature. Some of the collections also contained large series of immature worms, not listed above. Remarks The original description by Smith & Dickey (1918) is relatively complete and accurate, and little variation was observed among populations. This species shares several characters with others previously associated with Rhynchelmoides (Hrab˘e, 1961; Sokol’skaya, 1983). Because of the uncertain status of that genus, R. elrodi and most of the associated taxa are placed in ‘Group 2’ in the present account (see Discussion). The basic arrangement of the blood vessels and structure of the longitudinal muscles are consistent with most other Nearctic species in Groups 1 and 2, and contrast with most Palearctic species. The complete lack of an anterior vas deferens in R. elrodi is confirmed here, based on material from over 30 populations. The form of the penis sacs also appears invariant, but other distinguishing characters of the male reproductive system, including the prostates, insertion of the vas deferens, and the atrial musculature apparently vary slightly among populations, although they may also vary with maturity. Distinct penes inside eversible sacs is a character apparently shared with Group 1; however, differences in structure suggest that they may not be homologous. The penes of R. elrodi are much smaller, and appear to be simple extensions of the male duct without extensively modified tissue; very similar penes occur in R. glandula and Kincaidiana hexatheca Altman, 1936. The penis sacs of R. elrodi are relatively small, do not have glandular cells incorporated into them, and are associated with separate glands. There is little modification of the epidermis at the spermathecal pores, unlike R. brooksi and the species associated with Group 1. The short, tapered ectal duct of the spermatheca is relatively thick and glandular at full maturity, a character difficult to define, but shared with R. glandula, R. alaskana, R. saxosa and R. brooksi. The position of the spermathecal pores, posterior to the setae in X, also contrasts with Group 1. All specimens had the spermathecae connecting to the gut.
41
Figure 63. Rhynchelmis glandula, midventral gland in anterior segment (a) sagittal section (b) transverse section.
Rhynchelmis glandula Altman, 1936 Material examined: Washington: Undetermined location, probably collected near the University of Washington, Seattle, 12.III.1932 or 10.IV.1932. UWBM, Altman Collection, from the type series: 4 mature, sectioned specimens, labelled as series VIII, IX, X and XI, and several partially mature or immature. Thirteen unmounted, mature or near-mature worms in alcohol, apparently from the type series, vials labelled 161 (12.III.1932) and 161b (10.IV.1932). Sev-
eral immature specimens, vials 161c (14.V.1932), 161d (15.V.1932) and 161e (23.VI.1932). Jefferson Co.: Spring along the Hoh River, 29.IV.1999, coll. S. Fend. Four dissected, 5 mature and several immature worms in alcohol. Oregon: Josephine Co.: Illinois River at Sixmile Creek, 25.X.1999, coll. S. Fend. Three partially mature dissected worms, several in alcohol; tentatively identified as R. glandula. Yamhill Co.: Small, spring-fed pool, Peavine Ridge, near McMinnville, 5.XII.1999, coll. S. Fend. Two mature dissected, 3 in alcohol.
42 Supplemental description Size ranges given in Table 1. Male and spermathecal pores near posterior margin of segments X and VIII, on chaetal line between muscle bands. Circulatory system as described for R. elrodi; posterior lateral vessels have a laterally-inserting branch to gut starting near XL. Nephridia as described for R. yakimorum. Sacs, filled with undifferentiated cells, on septa in IX and X, usually in VIII, as described for R. yakimorum. Midventral, anteriorly directed sacs may also be present in these segments. Fully-mature worms with midventral glands in III– VII or IV–VII; partially mature worms from the 2 sites in Washington usually without glands, but small glands present on partially mature worms from 2 Oregon sites. Ectal pore of midventral glands not prominent, diameter near 50 µm. Gland masses primarily on either side of ventral nerve, to near 300 µm wide, consisting of several prostate-like bundles to 200 µm long with narrow cell extensions connecting to an ectal duct lined with columnar cells (Figure 63a,b). Spermathecal pores surrounded by distinct bundles of glands to 400 µm across (Figure 64). Male pores with small, eversible penis sacs and short penes, 60–70 µm long by 30–40 µm wide, as described for R. elrodi (Figure 65); glands at male pore absent or small and indistinct. Other characters of reproductive structures as described for R. elrodi. The material The sectioned specimens in the type collection were generally in good condition, but many series were incomplete, and few specimens were fully mature. The unmounted worms used for measurements were apparently mature, with well-developed male pores and midventral glands. No holotype was designated in the original collection. Collection labels in the vials are not detailed, and sometimes illegible, and refer to pool and spring habitats ‘near N.P. Track at bend’ and ‘below College Club’. The sectioned worms have no collection data, but appear to be from the indicated vials because those vials contain several unassociated tails. Of the 9 specimens having well-developed genital pores in the Hoh River collection, a single worm lacked the diagnostic midventral glands in the anterior segments. The aberrant specimen appeared fully mature, with sperm in the spermathecae, a distinct clitellum and well-developed eggs. The other worms in that collection, as well as the Oregon specimens, had the glands beginning on IV, instead of on III as
Figure 64. Rhynchelmis glandula, transverse section in VIII; spermatheca.
in the type series. The partially mature worms from the Illinois River, Oregon, had rudimentary atria and spermathecae, and were tentatively identified as R. glandula. The midventral glands had distinct ectal pores, but only small gland masses internally. Distinct glands were associated with the spermathecal pores in the most mature specimens. All specimens from that collection were distinguished from R. saxosa by well-developed lateral blood vessels in posterior segments. Remarks The original description (Altman, 1936) is relatively complete and accurate. Brinkhurst & Cook (1966) questioned the validity of R. glandula and synonymized it with R. elrodi on the basis that the primary difference, median ventral glands, appeared inconsistent. However, Holmquist (1976) reexamined the types and concluded that the differences were valid at the species level. Our examination of the type series and the new material from the Olympic Peninsula confirms that the presence of midventral glands is reasonably consistent in the Washington populations; they were present on all but one of the 26 fully mature specimens. Only fully-mature worms had this character in the Washington collections, but in the Oregon collections glands were also present on partially mature
43 similar tissue (without ducts) can be seen next to the ventral nerve cord of other species. Other characters used by Altman (1936) to distinguish R. glandula from R. elrodi include chaetal formula and size of individuals. Measurement of chaetal distance on small, variably-fixed worms is sufficiently imprecise that the slight difference indicated is a poor character. Our measurements of unmounted glandula from the original collection appear to refute Altman’s statement that glandula is generally larger than elrodi, and much greater size differences exist among populations of other Rhynchelmis species. However, the large clumps of glands at the spermathecal pores of glandula were another consistent difference, and may provide an an additional character to separate the two species. Although the presence of midventral and other glands appears to be a weak character, the apparent geographic separation of the two forms supports Holmquist’s (1976) decision to retain glandula. Rhynchelmis alaskana Holmquist, 1976 Figure 65. Rhynchelmis glandula, transverse section in X; male pore, penis everted.
worms. Mature worms from all north-coastal collections had midventral glands, whereas examination of many populations of R. elrodi from mid-continental sites did not produce any individuals having them at any stage of development. Although Holmquist (1976) stated that the structure of the midventral glands differed from those of the related R. alaskana, she did not elaborate, and it is not clear what differences exist. The glands in both species consist of a median pore, with distinct, multicellular lobes of glandular cells on either side of the ventral nerve cord, although some gland masses may be embedded underneath the ventral nerve. Their degree of development varies greatly among specimens. Midventral glands also occur in R. saxosa n. sp., and in some R. orientalis (Fend & Brinkhurst, in prep). Although apparently present only in some Group 2 species within Rhynchelmis, these glands may not constitute a unique apomorphy. Very similar structures have been described as ‘copulatory glands’ in the Enchytraeidae and Haplotaxidae (Stephenson, 1930; Chekanovskaya,1962), and are also illustrated by Isossimov (1962) for Lamprodrilus (=Teleuoscolex) baicalensis (Grube) in the Lumbriculidae. Similar glands occur in genital segments, lateral to the midline, in R. brooksi, R. malevici and possibly R. alyonae (Martin et al., 1998). In addition, small amounts of
Material examined: Alaska: Lake at 70◦ 22.50 N, 154◦ 380 W, 13.VII.1963, SMNH 4254. Holotype, 1 sectioned, mature specimen. Imuruk Lake, 653◦ 60 N, 163◦ 110 W, 22.VIII.1964, SMNH 990. Paratypes, 2 transversely-sectioned, 2 whole mounts, several in alcohol; all partially mature. Supplemental description Ventral blood vessel divides in VII, branches connect to single pair of commissural vessels in at least some anterior segments. Two pairs of lateral vessels per segment in VIII and posterior; both with long branches in posterior segments. Blood glands from VIII to about XVI. In VIII–XII, posterior lateral vessels connect to ventral vessel; in X and XI (at least) they loop into sperm and egg sacs. In XII and posterior segments, the anterior lateral vessel with a fork to the gut plexus, entering ventrolaterally. Nephridia as described for R. yakimorum. Midventral glands present in segments III–VII of mature or partially mature specimens, forming prostate-like bundles, primarily on either side of the ventral nerve cord, similar to Figure 63. Sacs on anterior septa extend into IX and X, associated with ventral diagonal muscle at septum. Holotype with spermatheca on one side passing through 8/9 into sac with loose epithelium; sac contiguous with the one on 9/10. On the other side, an empty cell accumulation or sac in IX, and spermatheca entirely in VIII.
44
Figure 66. Rhynchelmis alaskana, holotype; sagittal section in VIII; spermatheca.
Figure 68. Rhynchelmis alaskana, holotype; sagittal section; ental end of atrium.
distinct glands. Atria without any thickened muscle areas; diameter 50–70 µm in ectal portion, but bulging out between septa and expanding to near 150 µm entally, densely covered with prostates to ental end (Figure 68).
Remarks
Figure 67. Rhynchelmis alaskana, holotype, sagittal section in X; male pore.
Spermathecal duct thick-walled, tapered, as described for R. elrodi. Spermatheca with most sperm concentrated at the ectal end of the ampulla, just before the ectal duct; ental portion of ampulla with sparse, degenerate-appearing sperm (Figure 66). Penial sac weakly formed, without distinct penes; small papilla formed from short extension of male duct in small concavity with some development of muscle tissue (Figure 67). Male pore associated with a few
The original description is relatively complete, with a minor discrepancy. Holmquist (1976) showed the midventral glands entirely under the ventral nerve cord in R. alaskana, although the holotype and a transverselysectioned, partially mature paratype had gland lobes on either side of the nerve cord, as in R. glandula. Unlike the types of R. glandula, the ventral gland pores were prominent in partially mature worms from Holmquist’s collection. The blood vessels and nephridia were not discussed in the original description; both appear extensive, and very similar to most other Nearctic species. Of the Alaskan material we examined, only the holotype was fully mature; the series of paratypes examined contained only immature and partially mature worms. However, the actual size range appears about average for the genus, and much smaller than indicated by Holmquist (1976). The atria are similar to those of R. elrodi, but are more sac-like, and expanded entally. The small amount of muscle at the male pore forms only a very rudimentary penial sac.
45
Figure 69. Rhynchelmis saxosa, drawing of whole worm (a) mature, from Seventeen Mile Creek, Montana (b) partly mature, from spring near Coram, Montana.
Rhynchelmis saxosa n. sp. Holotype: USNM 186467, a dissected worm, mounted on slide. Type locality: Montana: Powell Co.: Cottonwood Creek, tributary to Blackfoot River, 4.VII.1997, coll. T. Smith and L. Smith. Paratypes: USNM 186468-186470: From the type locality, 4.VII.1997. Two sectioned worms (1 transverse and 1 sagittal), 2 dissected on slides. Other material: Montana: Flathead Co.: Spring near Coram, 16.VI.1996, coll. S. Fend. Partially mature worms; 5 sectioned, 2 dissected, 7 whole mounts, several in alcohol. Granite Co.: Harvey Creek, 24.X.1997. Partially mature; 1 whole mount, 2 in alcohol. Middle Fork Rock Creek, 7.IV.1997. One nearly mature, dissected, 2 partially mature in alcohol. Ranch Creek at Rock Creek Road, 5.VI.1998. Six mature (1 sectioned, 5 dissected). 8.V.1998. Five mature (1 sectioned, 4 dissected). 30.X.1998. Three partially mature (1 whole mount, 2 in alcohol). Lake Co.: Woodward Creek, tributary to Swan River, 22.VIII.1998. One mature, dissected, 5 partially mature in alcohol. Lewis & Clark Co.: Landers Fork, 21.III.1997. Four partially mature whole mounts. Petty Creek above falls, 31.VII.1998. Five partially mature (1 whole mount). Lincoln Co.: Lake Creek at Chase Cutoff, 10.IV.1997. One nearly mature, dissected. North Fork Keeler Creek, tributary to Lake Creek, 17.VIII.1998. One mature worm in alcohol. Seventeen Mile Creek at North Fork, 9.V.1996. Two mature worms (1 sectioned and 1 whole mount). Swan River at FR 966, 11.IV.1997. Two nearly mature, whole mounts. Missoula Co.: Blackfoot River at
Figure 70. Rhynchelmis saxosa, midventral glands in anterior segments of mature worms (a) sagittal section from Seventeen Mile Creek, Montana (b) transverse section from type locality.
46 Russell Gates, 22.III.1997. One mature and 1 near mature, whole mounts. Blackfoot River at Marco Flat, 14.IX.1996. One partially mature in alcohol. 9.IV.1997. One partially mature whole mount. Petty Creek, 30.X.1998. One mature, dissected. Rattlesnake Creek, 25.X.1997. One mature and 1 partially mature, dissected. Powell Co.: North Fork Blackfoot River, 12.IV.1997. Partially mature, 2 sectioned, 5 whole mounts. 21.IV.1997. Partially mature, 2 sectioned, 6 whole mounts. XI.1997. One partially mature, dissected. Oregon: Umatilla Co.: Denning Spring, on Pearson Creek, 23.IV.1999, coll. S. Fend. Six mature, dissected; 6 mature and several partially mature in alcohol. Washington: Clallam Co.: Bear Creek, tributary to Soleduck River, 28.IV.1999, coll. S. Fend. One mature and 3 partially mature whole mounts. Three partially mature in alcohol. All collected by D. L. Gustafson unless otherwise indicated. Etymology: saxosa (rocky), for the rocky stream habitat in the Rocky Mountains. Description Size variable, usually smaller than most other Rhynchelmis species, measurements in Table 1. Color of live worms pale, whitish. Prostomium with filiform proboscis up to 1 mm long. Anterior segments nearly circular in transverse section, annulation moderately pronounced, secondary annulation posterior to II. Chaetae simple-pointed, moderately sigmoid, with nodulus near 1/3 of distance from tip. Chaetae as short as 60 µm in II, usually near 160 µm in posterior segments. Male genital pores prominent, often on low protrusions, on chaetal line between ventral chaetae and 10/11. Spermathecal and female pores in VIII and XI, respectively; spermathecal pores on chaetal line, behind ventral chaetae (Figure 69a,b). Clitellum IX–XV. Pores of midventral glands prominent in fully-mature worms, either in slight depressions or on low protuberances between chaetae on III or IV–VII, sometimes in VIII; diameter near 30 µm (Figure 69a). Pores lined with elongate cells, connected to 1 or 2 bundles of glandular cells on either side of the ventral nerve cord; length of glandular mass up to 150 µm (Figure 70a,b). Midventral gland pores visible, but faint, on partially-mature worms (Figure 69b). Epidermis 20–40 µm thick in anterior segments, 40–100 µm in clitellum. Longitudinal muscle bands not tapered or curled at lateral margins, 25–35 µm thick; circular muscle layer near 5 µm thick. Pharynx II–IV, dorsal pad weakly developed. Pharyngeal glands IV–VI or VII. Testes paired in X, ovaries
paired in XI. Sperm sacs usually to about XXV, but sometimes extend beyond XL; egg sacs may extend a few segments posterior to sperm sacs. Commissural blood vessels in anterior segments a single pair of unbranched vessels joining dorsal vessel at mid-segment and ventral vessel (or branches) near posterior septum. A single, unbranched, posterior commissure pair in IX–XII has a short, thick portion dorsally and a longer thin portion extending to the ventral vessel. Commissures in X–XII form a loop extending into the sperm and egg sacs before joining the ventral vessel. Lateral blood vessels always absent from posterior segments. Blood glands small, in some clitellar segments. Nephridia usually begin in XIII; either paired, single, or absent in posterior segments. Nephridial ducts extensive, generally with dorsal and ventral loops and a simple ectal duct, as described for R. yakimorum. Tubules may cross septa midventrally. Tubules 15–20 µm thick, only slightly expanded to near 25 µm at ectal pore. Spermathecal pores without prominent glands or modification of the epidermis. Ectal ducts of spermathecae tapered, about 100–150 µm long and 50–60 µm wide at ental end, lined with columnar cells (Figures 71 and 72). Spermathecal ampullae may remain in VIII or extend as far as X. Ampulla with ectal expansion containing dark-staining sperm, followed by a narrower duct, followed by 1 or 2 nearly spherical ental expansions, as much as 300 µm wide in smaller worms, and over 500 µm in larger ones (Figures 71 and 72a), usually containing sparse, degenerate sperm. Spermathecae usually without gut connection, but one individual had one spermatheca connected to the gut (Figure 72b). Male pores on a small pad of thickened epidermal cells, surrounded by small clusters of glands about 100 µm across, but without distinct penes or muscular bulbs (Figure 73). Atria usually extend to XIII–XV, sometimes convoluted and restricted to X, total length 1200–2000 µm (Figure 74). Atrial diameter about 80 µm in ectal half, but expanded to about twice that width entally. Atrial muscle layer near 2 µm thick; lining cells cuboidal, not obviously glandular, near 15 µm thick where not expanded. Prostates multicellular, bundles about 50 µm long, as described for other species, but generally more sparse; distinct prostate bundles absent for 1 or 2 segments at ental end of atrium, although that portion may be surrounded by loose cells without obvious connections to the lumen (Figures 74 and 75). A single pair of male funnels, up to 200 µm wide, on 10/11. The single pair of vasa
47
Figure 71. Rhynchelmis saxosa, from Seventeen Mile Creek, Montana; sagittal section in VIII–IX; mature spermatheca with dense sperm in ectal portion.
deferentia free in X only; vasa enter atrial muscle near beginning of prostates and travel under muscle layer to near the ental end. The material As in the case of R. alaskana (Holmquist, 1976), mature specimens of R. saxosa were rare. This limits observations on variability of characters that might distinguish the two very similar species. Several of the many Montana collections contained large numbers of immature or partially mature worms, but only a small proportion was fully mature. Only the single Oregon collection contained a high proportion of mature worms. Partially mature worms could be easily distinguished from other Rhynchelmis species by their small size, the presence of midventral glands, and the lack of branched lateral blood vessels. A few specimens designated ‘nearly mature’ appeared mature except that the spermathecal ampullae were small and did not contain sperm. A single specimen had an extra atrium on one side in IX. Remarks There are few clear morphological differences between R. saxosa and R. alaskana. The most obvious is that the blood-vascular system of R. saxosa is strongly reduced compared with that of the R. alaskana type material, and more closely resembles that of R. brooksi and R. gilensis. In all populations of R. saxosa examined, the lateral vessels are completely
absent in posterior segments, rather than reduced in size and complexity – a character shared only with R. paraolchonensis (Giani & Martinez-Ansemil, 1984) and other species associated with Pseudorhynchelmis (Fend & Brinkhurst, in prep.). Although both species are unpigmented, the red-brown color noted by Holmquist (1976) as diagnostic for R. alaskana indicates that the extensive vascular development occurs consistently in that species. Although R. saxosa specimens are usually small, the individual body size varies among populations, and the reduction in vascular system cannot be attributed to small size alone. The combination of reduced vascular system and smaller size was considered sufficient by Hrab˘e (1961) to distinguish R. vagensis Hrab˘e, 1954 from R. limosella Hoffmeister, 1843. Unlike the R. alaskana holotype, the spermathecae of mated R. saxosa usually have very large ampullae, separated from the more ectal chamber by a narrower duct. However, Holmquist (1976) described the spermathecae of alaskana as highly variable. The glands at the spermathecal pore of R. alaskana (Holmquist, 1976) were not seen in any R. saxosa. The alignment of sperm cells in the spermathecae, with dark-staining cells concentrated in a chamber at the ectal end of the ampulla, is consistent with alaskana. This is also the case for R. orientalis, another species that may have midventral glands and has elongate spermathecal ampullae that do not connect to the gut (Fend & Brinkhurst, in prep.). As the ental portions of the ampullae of all three species contain degenerate sperm, it appears that the ental portions may be used to absorb excess sperm (an alternative to the direct transfer to the gut), while viable sperm for fertilization of eggs is retained in the ectal portion. This may not be unique to this group of species. Sperm cells are oriented toward the diverticula in some other Nearctic species (see above), as well as in the European R. tetratheca (Timm, 1979). The occurrence of a single R. saxosa individual having one spermatheca joining the gut, as in other Rhynchelmis species, suggests that reversal of this character is a likely occurrence. The aberrant spermatheca, with small ampulla and thick ectal duct, resembled spermathecae of R. elrodi. Although the sac-like atria, with expanded ental ends, are similar to those of R. alaskana, all specimens of R. saxosa had much less development of prostates. Multicellular prostates densely cover the ental part of the atrium in R. alaskana (Figure 68), but were absent from near the ental end of all R. saxosa atria. The male pores on both species are only weakly developed, but differ slightly; there is more muscle
48
Figure 72. Rhynchelmis saxosa, drawing of spermathecae, reconstructed from sagittal sections (a) normal, from type locality; (b) atypical, connected to gut, from Seventeen Mile Creek, Montana.
Figure 73. Rhynchelmis saxosa, from Seventeen Mile Creek, Montana; sagittal section in X; male pore.
49
Figure 74. Rhynchelmis saxosa, from type locality; drawing of atrium from dissection.
Figure 75. Rhynchelmis saxosa, from type locality; transverse section of ental end of atrium.
development in the alaskana holotype (Figure 67), whereas the montana specimens have a small pad of thickened epidermis. The short posterior vasa deferentia, the wedge-shaped spermathecal duct, and the absence of anterior vasa deferentia all suggest affinity with Group 2. As in the case of R. alaskana, the midventral glands were prominent in partially-mature worms. In mature R. saxosa specimens they were often on distinct protuberances. Annulation was pronounced in some of the R. saxosa material, a character used by Holmquist to distinguish partially-mature specimens of a possible new Alaskan species from typical alaskana. Rhynchelmis brooksi Holmquist, 1976 Material examined: Alaska: Wild Lake, 67◦ 300 N, 151◦ 360 W, 26.VIII.1964, SMNH 4255. Holotype, 1
sagittally sectioned worm. Paratype series A, B, M, L (all sectioned), and a whole mount. Lake at 69◦ 56.60 N, 154◦ 5.90 W, 24.VII.1969, SMNH 998. One sectioned, 2 whole mounts, several in alcohol. Supplemental description Ventral blood vessel divides near 6/7, with 2 forks anteriorly. Posterior commissures join ventral vessel in VIII–XII, after looping into the sperm and egg sacs in X–XII. Unbranched anterior pairs of lateral vessels may start in VIII or more posteriorly; very short in first few segments, usually forming a short loop to the gut plexus. From about XX lateral vessels terminate at ventrolateral part of gut. Nephridia occur regularly or irregularly. Nephridial structure similar to other species, with dorsal and ventromedian tubules. Ventromedian tubules not strongly associated with ventral vessel; may cross
50
Figure 77. Rhynchelmis brooksi, male pore. Figure 76. Rhynchelmis brooksi, transverse section in VIII showing ventral gland and spermathecal pore.
septa and may extend 1 or 2 segments anterior to first postseptale. Dorsal tubules not associated with the lateral blood vessel. Ectal duct a simple tube, with inconspicuous nephridopore. Loose sacs of cells usually present on anterior septum in IX and/or X, but weaker and more irregular than in other species. Irregularly-occurring ventral glands in VIII/X with large clumps of gland cells, with bundles of ducts connected to an ectal pore (Figure 76). Spermathecal and male pores on large pads of modified epidermal cells covered by a layer of distinct, prostate-like glands, interspersed with muscle fibers to dorsolateral body wall (Figures 76 and 77). Spermathecal diverticula are bulb-shaped outpocketings from ampulla. Spermatheca does not pass through septum. Ectal duct of spermatheca thick and wedgeshaped, nearly filled with elongate lining cells having nuclei arrayed peripherally (Figure 76). Prostates mostly multicellular, pear-shaped bundles, but tightly packed and difficult to distinguish (Figure 78). Vasa deferentia may be closely appressed to atrium in region with prostates, but penetrate muscle layer for a short distance at most.
Figure 78. Rhynchelmis brooksi, sagittal section; prostata in bundles.
Remarks The original description is accurate and detailed, except that the blood vessels and nephridia were not discussed. The reduced circulatory system of this species differs from most Nearctic species, but is similar to other species that are relatively small, R. gilensis and R. saxosa. It was difficult to see the minute chaetal forks described by Holmquist (1976) on most speci-
51 mens, and it is possible that they have been missed in descriptions of other species. Holmquist (1976) stated that the prostate cells in Rhynchelmis alaskana are in bundles, but in Rhynchelmis brooksi she described them as forming a more or less continuous mass. Reexamination of the type material of brooksi reveals that prostate cells are generally in bundles, as in other Rhynchelmis species. However, the bundles have fewer cells and are tightly packed, making them difficult to distinguish. On the basis of overall similarity, R. brooksi is very close to the Siberian R. malevici, differing primarily by the chaetal forks, the slightly median position of the genital pores, and position of the anterior nephridium (Sokol’skaya, 1983). These last two characters have generally been applied at the sub-specific level elsewhere in the genus and in the Lumbriculidae, and the nephridial position tends to vary within populations of other species. Other possible differences include the small spermathecal diverticulum and the pads of thickened cells surrounding the male and spermathecal pores of R. brooksi. These latter characters were not mentioned in the description of R. malevici. Distribution and ecology of Group 2 species Most confirmed collections of fully-mature R. elrodi were from western Montana and eastern Idaho, from a wide variety of habitats (Figure 80). The single Utah collection may represent an introduction, as the location is immediately below a former fish hatchery, although partially mature Group 2 specimens from southern Idaho and northern Utah are also likely to be this species (collection data given below with unattributable material). R. elrodi is the dominant Rhynchelmis species in a large series of Montana collections, often occurring in somewhat degraded sites (D. L. Gustafson, pers. comm.). R. elrodi often occurred with R. saxosa n. sp., and at one site each with R. gustafsoni and R. rostrata, but its range usually extended farther downstream than other Rhynchelmis species. It is the most common Rhynchelmis species we have confirmed from east of the continental divide, in collections from several tributaries of the upper Missouri River. Most collections contained worms at a wide range of maturation, indicating low reproductive synchronicity within populations. A few collections from the lower Columbia and Yakima Rivers in Washington (collection data given below with unattributable material), contained immature worms having the position of male and spermathecal pores resembling R. elrodi. This implies either a substantial range ex-
tension, confusion with R. glandula, or yet another undescribed species. Specimens from Goose Creek Meadow, Idaho (USNM 26346) attributed to this species by Brinkhurst & Cook (1966) proved to be a variant of R. yakimorum. Other collections cited in that publication, including ones from Alaska, North Carolina and Wyoming, were unavailable for verification. Most or all of the fully-mature R. glandula in the Altman collection appear to have been collected at one or two sites near Seattle, Washington, although collection data of are incomplete. Habitats listed are muck and debris at the bottom of a spring, and leaves in a freshwater pool. An attempt to locate the type locality in April, 1999, suggested that the habitat has been destroyed by urban development. Altman (1936) stated that the species is widespread in the coastal northwest, but there was no material from other sites in his collection. Two of his collections from river sites in southern Washington contained immature specimens that appeared to be Kincaidiana hexatheca Altman, 1936. Subsequent collections support a general northcoastal distribution: the species occurs in springs on the Olympic peninsula, possibly along the southern coast of Washington (immature worms only; collection data given below with unattributable material), and in coastal Oregon. The population at the type locality appears to have highly synchronous development. Fully mature worms were only collected in March and April; those from May and June were all immature. Associated worms in the recent collections included K. hexatheca, Rhyacodrilus montana, an undescribed Eclipidrilus species, and an undescribed lumbriculid genus. R. alaskana and R. brooksi have been collected in a number of lakes in northern Alaska (Holmquist, 1976), and we are not aware of any collections other than the type series. R. saxosa appears isolated from the original alaskana collections, but its northern distribution limits are unknown, and the intervening region is poorly collected. R. saxosa was primarily collected from coarse substrata in river habitat, but it also was abundant in a cold, gravel-bottom spring. In rivers, it was most abundant in sand/gravel pockets around large boulders, often deep in the sediment. Mature worms were collected from March to October, but most were from May to July. However, other collections from the same months contained only immature or partially mature worms. R. saxosa was occasionally a numerically dominant species in the benthos (D. L. Gustafson, pers. comm.). Although sites with co-occurring Rhynchelmis species are rare,
52
Figure 79. Map of western USA, showing collection sites of species in Group 1.
most R. saxosa collections also included R. elrodi. R. yakimorum variant 2 also occurred at the Oregon site.
Unattributable material: Material examined: British Columbia: Hidden Creek at Spuzzum, VI.1977, coll. R. O. Brinkhurst. Two dissected, immature worms, labelled R. elrodi. Fraser River at Vancouver, 26.VIII.1973, coll. R. O.
53
Figure 80. Map of western USA, showing collection sites of species in Group 2.
Brinkhurst. One immature whole mount, labelled R. elrodi. Idaho: Franklin Co.: Bear River at Preston, 5.III.1997, coll. D. L. Gustafson. Many immature worms in alcohol. Mississippi: Unknown locality, 1924, collector unknown. USNM 26397, several immature worms in alcohol. Utah: Cache Co.: Spring along Blacksmith Fork, near Logan, 22.IX.1997, coll.
R. D. Kathman. Three partially mature in alcohol. Spring Creek at Allred Point, 21.IV.1997, coll. R. D. Kathman. One partially mature. Washington: Benton Co.: Yakima River at Whitstran, 1.XI.1988. One whole mount. Yakima River at Van Giesen Bridge, 30.X.1987. One dissected. Marion Drain, 30.X.1987. One dissected. Columbia River below Priest Rapid
54 Dam, 24.X.1995. Two whole mounts. Kittitas Co.: Tucquala Creek, 14.VI.1996. One whole mount. Pacific Co.: Spring beside North Fork Nemah River, 30.IV.1999. Immature worms; 3 whole mounts and 3 in alcohol. Spring along Naselle River, 30.IV.1999. Immature worms; 2 whole mounts and 6 in alcohol. Collected by S. Fend, unless otherwise noted. Remarks The Mississippi specimens were all in poor condition and probably immature. The position of the genital pores and the arrangement of blood vessels could not be determined. The small size of these worms suggests that they may belong to another genus; proboscisbearing species of both Eclipidrilus and Trichodrilus occur in the southeastern U.S.A. We were unable to obtain specimens for the only other published eastern North American record, from North Carolina, attributed to R. elrodi by Brinkhurst & Cook (1966). Based on the position of the genital pores, the partially mature specimens from the lower Yakima and Columbia Rivers in Washington, the Bear River in southern Idaho, and Spring Creek, Utah are associated with Group 2. As all of these specimens had branched, lateral blood vessels in the posterior segments, they are likely to be R. elrodi or R. glandula. The single, partially-mature specimen from Tucquala Creek, a headwater site in the Yakima Basin, did not have lateral blood vessels and could, therefore, be R. saxosa. Additional Utah material, from Blacksmith Fork, was apparently partially-mature R. rostrata. Although Brinkhurst (1978) reported R. elrodi from British Columbia, the only available specimens were immature and could not be associated with a species group.
Discussion Distribution The North American Rhynchelmis s. lat. fauna now includes 11 species, but some of these show considerable regional variability, and may represent species complexes. All occur in the western part of the continent, typically in montane or coastal regions. Earlier records from eastern North America were apparently misidentified, or were unavailable for verification in this study. Although they are common in some western mountain ranges, Rhynchelmis species appear to be absent from those encompassed by the Great Basin, and, despite some searching, the genus has not been
collected in the southern parts of the Sierra Nevada or Coast Range. It is likely that more species or forms will be discovered. Montane regions that appear notably under-collected include the southern Rocky Mountains and most of western Canada. The two species groups have somewhat different distributions. Group 2 extends from Alaska southward to Oregon and Utah. Group 1 species were not collected in Holmquist’s (1976) survey of northern Alaska, and the group generally appears to have a more southern distribution, with several records from the Coast Range and Sierra Nevada in central California, and from slightly south of the Rocky Mountains in Arizona and New Mexico. Rhynchelmis is poorly represented in benthic collections, and, like other oligochaetes, is often not identified in surveys of aquatic invertebrates. Although information on Rhynchelmis distributions is limited, a few generalizations can be made. For the most part, species and forms discussed here have limited ranges, with minimal overlap. Species rarely co-occur at a site, the main exception being the sites with both R. saxosa and R. elrodi. Although some species appear to show habitat specificity (R gilensis and R. saxosa in gravel patches in fast current), others inhabit a wide range of aquatic habitats, including springs, ponds and rivers. The genus is common in lentic habitats in the northern part of its range (R. alaskana and R. brooksi in Alaska), but most other collections are from lotic habitats. The highest densities usually occur in spring runs or in lower rhithral portions of rivers. As a group, the Lumbriculidae appear to be cool-stenotherms (Timm, 1980), with few exceptions. The basic requirement for Rhynchelmis appears to be a stable substratum in cool, well-oxygenated water. Most records are from forested landscapes with limited human impact on aquatic resources. The dispersal mechanisms of Rhynchelmis species are unknown. Longitudinal movement within river systems is certain, even where the worms are essentially restricted to protected habitats such as tributary springs (e.g. R. utahensis). However, species appear to be restricted to limited portions of a given river system, and apparently differ in their environmental requirements. The more general distribution of R. elrodi in Montana, compared with the sympatric R. saxosa and R. gustafsoni, may result from a greater tolerance of conditions in lower river reaches. Dispersal also appears to occur across drainage divides. The high densities of some populations in springs suggests that they may disperse via groundwater, but other intermediate aquatic habitats may occur within mesic, forested
55 landscapes. For example, R. monsserratus occurred in a snowmelt marsh at one drainage divide. Recent speciation within the genus is suggested by the R. yakimorum complex and regional variants described here, as well as some closely-related species pairs (e.g. R. glandula and R. elrodi; R. alaskana and R. saxosa; R. brooksi and R. malevici). Although a discussion of processes involved in speciation is premature until distributions are better known, vicariance is likely to prove important on the basis of landscape features and the assumed low mobility of these worms. North-south mountain ranges alternate with relatively warm-xeric intermountain areas over most of western North America. Aquatic habitats in valleys are characterized by higher temperatures and finer sediments, and in modern times, habitat quality is further degraded by intensive agricultural and urban land use. The latter habitats appear unsuitable for Rhynchelmis, and probably isolate worm populations, especially in the southern part of the region. However, repeated climatic changes likely have resulted in alternating periods of dispersal and isolation, as documented for Quaternary vegetation patterns, and inferred from distributions of other animals (e.g. Frey, 1965). Taxonomy The genus Rhynchelmis s. lat. is currently defined as having spermathecal pore(s) in VIII, a single pair of male pores in X, female pores at 11/12, and long, cylindrical atria covered with pyriform clusters of prostate cells (Cook, 1971). Other characters, although often distinctive, vary within the genus. The prostomium typically terminates in a distinct proboscis, and the spermathecae communicate with the gut in many species. Functional or non-functional anterior vasa deferentia may communicate with funnels on 9/10, and additional spermathecae sometimes occur in IX. Most species included within the broad definition of Rhynchelmis can be associated with one of four species groups, considered genera by some authors (e.g. Hrab˘e, 1982). These groups roughly correspond to Rhynchelmis s. str., Pseudorhynchelmis Hrab˘e, 1982, Sutroa Eisen, 1888, and Rhynchelmoides Hrab˘e, 1936. Two of the four previously defined species groups within the broad definition of Rhynchelmis are entirely Palearctic, and are not discussed in detail here. Rhynchelmis s. str. is defined by longitudinal muscle bands having attenuated margins that curl into the coelom, at least in preserved worms (Hrab˘e, 1936). A distinctive organ, sometimes termed a ‘rudiment-
ary atrium’ (e.g. Cook, 1971), occurs in IX in some species. The development of anterior vasa deferentia and associated testes, the proboscis, and the blood vessels vary considerably among these species. Pseudorhynchelmis was created for R. olchonensis Burov, 1932, a Lake Baikal endemic with several characters that appear to be plesiomorphic within the Lumbriculidae: longitudinal muscles not curling inward, prostomium without proboscis, no connection of the spermathecae to the gut, testes in IX and X, and two pairs of functional vasa deferentia (Hrab˘e, 1982). Some of these characters are unusual within Rhynchelmis s. lat., but occur sporadically within Rhynchelmis s. str. or Rhynchelmoides. Two additional characters noted by Hrab˘e for R. olchonensis (vasa deferentia much wider entally than ectally, and penes distinctly developed in penis sacs) are possible apomorphies, but they are poorly described in some other Rhynchelmis species. Four species subsequently described from Lake Baikal and western Europe share many of these characters, as well as other, apparently plesiomorphic characters distinguishing them from other Rhynchelmis s. lat.: the posterior vasa deferentia enter XI, and the atria are relatively short. Although Martin et al. (1998) considered these species to form a complex, the authors have retained Rhynchelmis for them, being unable to define a distinct apomorphy for Pseudorhynchelmis (Giani & Martinez-Ansemil, 1984; Martin et al., 1998). Of the two species groups considered in this account, Group 1 is entirely Nearctic. Sutroa was originally defined by the single median spermatheca of R. rostrata. The addition of five new species related to R. rostrata, having paired or unpaired spermathecae in VIII, argues against using this character by itself in defining the genus or species group. The occurrence of occasional individuals having additional spermathecae in VII or IX in most Group 1 species also suggests that spermathecal position is a weak character. Unpaired versus paired reproductive organs were also traditionally used to separate genera now included in the lumbriculid genus Eclipidrilus, but Wassell (1984) did not even consider this valid at the subgeneric level, preferring characters related to morphology of these organs. One species of Eclipidrilus has been shown to have paired or single atria within a single population (Brinkhurst, 1998), although in this case the usual lateral position is maintained. Holmquist (1976) also noted the large penial bulbs of R. rostrata, and retained Sutroa as a genus, despite the earlier combination of Sutroa with Rhynchelmis by Brinkhurst & Cook (1966). Rhynchelmis gilensis and the four species in the yakimorum complex all
56 have male ducts with large, eversible penial bulbs, a character unique within Rhynchelmis. However, the occurrence of similar structures in other genera of Lumbriculidae, as well as Enchytraeidae, suggests that penial bulbs of different species may not be homologous and their presence alone may be a weak character for designating a genus. Several additional characters distinguish the species in Group 1. The ectal pore(s) of the spermatheca(e) are anterior to the ventral chaetae, rather than near 10/11 as in all other Rhynchelmis s. lat. The basic structure of the spermathecae is consistent, with two or more diverticula originating in the ectal duct, and large, invaginated ectal bulbs of modified (possibly glandular) epidermis and muscle. R. brooksi and four or five Palearctic Rhynchelmis s. str. species have at least one diverticulum on each spermatheca, but these appear to be outpocketings of the ampulla rather than distinct structures originating at the spermathecal duct (e.g. Timm, 1979). All species in Group 1 possess an anterior pair of nonfunctional vasa deferentia and funnels, a character shared with R. orientalis and some Rhynchelmis s. str. Prostates are absent in at least the ectal 1/3 to 1/2 of atrium of all species, a character shared with R. brooksi, R. malevici and possibly R. orientalis. The lateral positions of spermathecal and male pores are variable, but sometimes medial to the chaetal line; this character also occurs in some species associated with Pseudorhynchelmis and Rhynchelmis s. str. Rhynchelmis Group 1 could be interpreted as forming a series with respect to the lateral positions of the genital pores. R. utahensis and variant 2 of R. yakimorum are similar, approaching the typical condition for the genus, with male and spermathecal pores on or near the chaetal line. Among the other species and forms, spermathecal pores range from slightly inside the chaetal line (typical R. yakimorum) to closely appressed (R. yakimorum variant 1 and R. gustafsoni), to near-median and single (R. monsserratus, R. rostrata and R. gilensis). Male pores range from the chaetal line (most R. yakimorum) to somewhat median (R. rostrata, R. gilensis) to nearly fused medially (R. gustafsoni). Male pores do not appear to match the spermathecal positions in R. monsserratus. Although they are not median in yakimorum variant 1, R. gilensis and R. rostrata, they are medially directed, i.e. towards the spermathecal openings. Species in the mostly Nearctic Group 2 have been associated with Rhynchelmoides Hrab˘e, although some subsequent authors have retained Rhynchelmis. Hrab˘e (1936) created the genus Rhynchelmoides
for R. elrodi, to distinguish it from the Palearctic species having curled longitudinal muscle bands. Later, Hrab˘e (1961) transferred Rhynchelmis glandula Altman, 1936 to Rhynchelmoides. Although this was rejected by Cook (1971), a third species, the Palearctic Rhynchelmoides malevici, was described by Sokol’skaya (1983). That author stated that Rhynchelmis brooksi, Rhynchelmis alaskana, and a species termed Rhynchelmis sp., all described by Holmquist (1976), should also be transferred to Rhynchelmoides. She suggested that the Palearctic Rhynchelmis orientalis Yamaguchi, 1936, also be included because, although it was described as having eight longitudinal muscle bands, they are not curled inward. Although the original defining character for Rhynchelmoides, non-curled muscle bands, is shared with Group 1, several additional characters distinguish some or all members of Group 2. However, most of these appear to be plesiomorphic, or are inconsistent. All species in Group 2 have spermathecal pores posterior to the ventral chaetae, on the chaetal line. Male and spermathecal pores lack ectal bulbs of modified epidermis and muscle, although there may be separate gland cells and small penial sacs. Penes are, at most, a short extension of the atrium, often only a small papilla. Spermathecae are always paired in VIII, without diverticula, except in R. brooksi and R. malevici. With the exception of R. orientalis, the anterior vasa deferentia and funnels are absent, and the ectal ducts of the spermathecae are wedge-shaped, with a thick layer of glandular lining cells. Except for the latter three species (and rare specimens of R. elrodi), the (posterior) vasa deferentia enter the atrial muscle near the ectal end, and prostates begin near the ectal pore of each atrium. The atria are not divided into histologically distinct regions, except for R. brooksi and R. malevici, but as these two species appear unique in other respects, they may not belong in Group 2. One of the new species, R. saxosa, also can be associated with Group 2 on the basis of two additional characters. The midventral row of glands in anterior segments of R. saxosa is also found in R. alaskana, R. glandula and possibly R. orientalis (Fend & Brinkhurst, in prep.). The lack of a spermathecal gut connection, otherwise only found in the species associated with ‘Pseudorhynchelmis’, is shared with R alaskana and R. orientalis, and like the latter two species, the ampulla is differentiated into an ectal portion having viable sperm and an ental portion with degenerate sperm.
57 R. brooksi and the very similar R. malevici are not readily associated with other groups of Nearctic (or Palearctic) Rhynchelmis s. lat. The atria, described by Holmquist (1976), appear histologically unique, having three major sections. The differentiation of the ectal portion from the prostate-covered ental portion resembles Group 1, whereas the thick, glandular middle portion is unknown in the other Nearctic species, and resembles the atrium of some Baikal species associated with Pseudorhynchelmis Hrab˘e (Martin et al., 1998). The large and irregularly-occurring glands associated with the genital pores are very similar to the midventral glands of R. alaskana and R. glandula. As their structure is rather simple and generalized, this may not indicate homology. The thickened pads of tissue with associated glands at the male and spermathecal pores, although never invaginated, are rather similar to the ectal bulbs of R. rostrata and R. yakimorum, and may be intermediate between bulbs and the clustered glands of other species. The glands covering the pad are more distinct than in the penial and spermathecal bulbs of R. yakimorum. The thick, glandular spermathecal duct, expanded at the ental end, resembles that of R. elrodi and R. alaskana. The single spermathecal diverticulum of R. brooksi appears to be an outpocketing of the ampulla, and is more similar to that of some European Rhynchelmis s. lat. species than it is to other Nearctic species. The above groupings are based on overall similarity, rather than formally proposed apomorphies. Although some characters appear distinctive enough to be considered apomorphies for the various groups, we currently take the conservative approach of attributing the new species to Rhynchelmis s. lat. A thorough cladistic analysis of the genus will require assessment of new characters for the Palearctic species, which will be discussed in a subsequent contribution. Preliminary analyses, using the available characters, have failed to provide clear apomorphies or consistent groupings.
Key to Nearctic Rhynchelmis 1. Spermathecal pore(s) anterior to ventral chaetae, lateral position variable, may have single median spermatheca in VIII. Spermatheca(e) with two or more diverticula originating in the ectal duct and large, invaginated ectal bulbs of modified epidermis and muscle. Male ducts with distinct, eversible penial bulb. Anterior vas deferens and funnel present but nonfunctional; posterior vas deferens usually enters atrial muscle near mid-
point of atrium. Prostates absent in at least ectal 1/3 of atrium. Group 1 (includes Sutroa Eisen) . . . . . . . . . . . . . 2. 10 . Spermathecal pores posterior to ventral chaetae, on the chaetal line. Spermathecae always paired in VIII, without diverticula; may have gland cells not associated with ectal bulbs of modified epidermis and muscle; ectal ducts wedge-shaped, with columnar, glandular lining cells. Male ducts without distinct, eversible penial bulb; may have small penial sac and /or separate ectal glands. Anterior vas deferens and funnel absent; posterior vas deferens enters atrial muscle near ectal end. Prostates begin near ectal pore of atrium, usually in X. Group 2 (includes Rhynchelmoides Hrab˘e) . . 11. 00 1 . Spermathecal pores posterior to ventral chaetae. Spermathecae with single diverticulum originating at ampulla; ectal ducts with thick layer of glandular lining cells. Male and spermathecal pores with a pad of thickened epidermis and gland cells, may be associated with larger glands. Atria with 3 distinct regions: ectal third is relatively unmodified; the middle third with thick, glandular lining cells; the ental third with prostates. Anterior vas deferens absent; posterior enters atrium near ental end. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . R. brooksi 2. Spermatheca single, near median. Spermathecal diverticula tubular, with long branches or clubshaped. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3. 20 . Spermathecae single or paired. Paired Spermathecal diverticula with 3–10 short lobes. . . . . . . . . . . . . . . . . . . . . 6. R. yakimorum complex 3. Spermathecal diverticula more than 2, usually 6; long tubes with length more than 10 times diameter, originating at long ectal duct. Spermathecal ampulla broadly ovate. Atria extend through several segments; thick muscle in ectal half and prostates covering at least the ental 1/2. Posterior vas deferens enters atrium medially; anterior vas embedded in muscle. Posterior lateral blood vessels long, paired, and branched. Nephridia with simple, tubular ectal duct. Large worms, greater than 1 mm diameter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4. R. rostrata 0 3 . Spermathecal diverticula 2, club-shaped. Ental duct of spermatheca slightly widened, forming an indistinct ampulla. Atrium usually coiled in X–XI,
58 without thick muscle layer in ectal half; prostates limited to the ental 1/3–1/4. Vasa deferentia joining and entering atrium entally. Posterior lateral blood vessels short, unbranched. Nephridia with bulbous expansion at ectal duct. Small worms, less than 1 mm diameter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . R. gilensis 4. Ventral chaetae longer and thinner than dorsals, with proximal nodulus. . . . . . . . . . . . . R. rostrata, (Lake Tahoe) variant 2 40 . Ventral chaetae similar to dorsals, nodulus distal. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5. 5. Most spermathecal diverticula with 1–3 branches . . . . . . . . . . . . . . . . . . . . . . . . . R. rostrata variant 1 (includes Sutroa alpestris Eisen) 50 . At most 1 or 2 branches on 1 or 2 spermathecal diverticula. . . . . . . . . . . . . . . . . . . . . . .R. rostrata, typical form 6. Penial bulbs taller than wide, with distinct penes when retracted; strongly attenuated atrium enters on median face of bulb. Everted penes acuminate, longer than wide, curved medially. Atrial muscle only slightly thicker ectally than entally. Ental part of atria with indistinct lining cells, prostates very granular. Spermathecae paired, with pores on or slightly outside chaetal line. Spermathecal ampulla heart-shaped, almost as wide as ectal bulb. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . R. utahensis 0 6 . Penial bulbs nearly spherical, penes indistinct (shorter than wide) when retracted; atria enter bulbs dorsally. Everted penes blunt. Atrial muscle much thicker ectally than entally. Ental part of atria with distinct lining cells, prostates only slightly granular. Spermathecae paired or single, position of pores variable. Spermathecal ampulla pyriform, not more than half as wide as ectal bulb. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7. 7. Spermathecae single, near median. Penes not apparent when bulbs are retracted. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . R. monsserratus 0 7 . Spermathecae paired. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8. 8. Both spermathecal and penial bulbs contiguous, each with paired pores in single ectal opening. Penes short but distinct, directed anteriorly both when retracted and when everted. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . R. gustafsoni
80 . Male pores widely separated, on or near chaetal line. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9. 9. Spermathecal pores contiguous, with paired pores in single ectal opening. Penes not apparent when retracted; male pores directed medially in retracted penial bulb. . . . . . . . . . . . . . . . . . . . . . . R. yakimorum variant 1 0 9 . Both male and spermathecal pores and ectal bulbs widely separated. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10. 10. Spermathecal pores slightly inside ventral chaetal line. Retracted penes very short but distinct, length about 1/4 width, directed anterolaterally. . . . . . . . . . . . . . . . . . . .R. yakimorum, typical form 100 . Spermathecal pores on or slightly outside the ventral chaetal line. Retracted penes about as long as wide, conical; directed ventrally when retracted or everted. . . . . . . . . . . . . . . . . . . . . . . R. yakimorum variant 2 11. Spermathecae with elongate ampullae that do not connect to the gut. No penial sacs; at most a slight epidermal thickening and short papilla. Midventral glands in preclitellar segments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12. 110 . Spermathecae with short ampullae that connect to the gut in VIII. Small but distinct penial sacs, with distinct penes. Midventral glands variable. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13. 12. Spermathecal ampullae with greatly distended ental ends. Atria without prostates entally. No lateral blood vessels posterior to XII. Small worms, usually less than 1 mm diameter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . R. saxosa 120 . Spermathecal ampullae less distended. Atria with dense prostates to ental end. Posterior lateral blood vessels paired, branched. Larger worms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . R. alaskana 13. Midventral glands present in III or IV–VII of mature worms. Large glands at spermathecal pores. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . R. glandula 0 13 . No midventral glands. Spermathecal pores with small, indistinct glands, or without glands. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . R. elrodi Acknowledgements We are indebted to R. D. Kathman, P. Rodriguez, T. Timm and M. J. Wetzel for reviewing various
59 drafts of the manuscript. D. L. Gustafson provided many collections from extensive surveys of aquatic oligochaetes in Idaho and Montana. Drafts of new descriptions and type specimens were provided by P. Martin. A. Ohtaka located the missing types of R. orientalis and sent additional material. D. McKeyFender, W. Foster, R. D. Kathman, T. Smith and L. Smith provided specimens from field collections. Museum specimens were provided by K. Sindemark (Swedish Museum of Natural History), M. Lowe (British Museum of Natural History), W. Moser and C. Bright (U.S. National Museum), R. Crawford (Burke Museum, University of Washington, Seattle). S. Renkes assisted with graphics and P. Marrero assisted with the production of the ms.
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