ISSN 0032-9452, Journal of Ichthyology, 2007, Vol. 47, No. 8, pp. 669–672. © Pleiades Publishing, Ltd., 2007. Original Russian Text © N.V. Parin, A.N. Kotlyar, 2007, published in Voprosy Ikhtiologii, 2007, Vol. 47, No. 5, pp. 707–710.

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On Finding of Shark of the Genus Somniosus (Squalidae) at the Submarine Ridge of Nazca (Southeastern Pacific) N. V. Parin and A. N. Kotlyar Institute of Oceanology, Russian Academy of Sciences—IORAS, Nakhimovskii pr. 36, Moscow, 117218 Russia e-mail: [email protected] Received April 20, 2007

DOI: 10.1134/S0032945207080140

The genus Somniosus (sleeper sharks) tradionally being considered containing three species (Compagno, 1984) has been recently revised by Yano et al. (2004) who assumed two subgenera in it: Somniosus with three species, i.e., S. (S.) microcephalus (the northern Atlantic Ocean and adjoining waters of the Arctic Regions), S. (S.) pacificus (the northern Pacific and adjoining seas), and S. (S.) antarcticus (the southern hemisphere); and Rhynoscymnus with two species, i.e., S. (S.) longus (waters of the southern Japan and New Zealand) and

S. (S.) rostratus (the Mediterranean Sea and adjoining waters of the Atlantic ocean). In the southeastern Pacific, the sharks of genus Somniosus were noted only twice (both times under the name S. pacificus), i.e., in the area of Valparaiso, Chile (about 37° S) and off the coast of Peru between 11 and 14° S (Pequen˜o et al., 1998; Chirichigno, 1998). Unfortunately, both the latter work and information about the capture of one specimen, more conventionally classified as S. rostratus, remained unknown for the authors of revision (Parin, 1990; Parin, 1991; Parin et al.,

Fig. 1. The sleeper shark Somniosus (TL in its lifetime about 140 cm) caught at the Nazca submarine ridge (19°35′ S, 80°13′ W) on the deck of R/V Professor Shtokman.

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(c)

(a)

1 mm

(b)

1 mm Fig. 2. The upper jaw (a) and lower jaw (b) teeth and dermal denticles (placoid scales) on the upper surface of the head (c) in Somniosus sp. from the Nazca submarine ridge.

1997). This shark was caught in the 18th trip of the R/V Professor Shtokman that took place in April–May 1987 and was specially dedicated to studying the bioresources of the Nazca and Sala-y-Gomes submarine ridges (Parin et al., 1988). It was caught at night by a trap net at the northernmost mountain of the Nazca submarine ridge (Nachal’naya mountain, 19°35′ S, 80°18′ W, depth of 800 m). The total length of the species (TL) in its lifetime was about 140 cm (Fig. 1). The

fish, preserved by formalin in a small barrel with a diameter of about 50 cm, was delivered to Moscow, and now it is kept in the Zoological Museum of Moscow State University (MGU) under number P-21708 (now its total length is 111.9 cm). The basic measurements of our specimen are made according to the key of Yano and coauthors (2004) with consecutive numbering of characters (in parentheses) by the data of the same authors. Measurements (% of TL): (1) from the top of JOURNAL OF ICHTHYOLOGY

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ON FINDING OF SHARK OF THE GENUS SOMNIOSUS (SQUALIDAE)

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Fig. 3. General view of jaws in Somniosus sp.

snout to the external nostrils 4.3, (2) to the eye 6.4, (3) to the spiracle 11.5, (4) to the mouth 9.3, (5) to the first gill opening 18.9, (6) to the second gill opening, 20.6, (7) to the third gill opening 22.2, (8) to the fourth gill opening 23.9, (9) to the fifth gill opening 25.9, (10) to the beginning of the pectoral fin 26.8, (11) to the beginning of the ventral fin 62.6, (12) to the cloaca 64.3, (14) to the beginning of the first dorsal fin 44.7, (15) to the beginning of the second dorsal fin 67.9, (16) to the beginning of the upper lobe 80.4, (17) to the beginning of the lower caudal lobe 79.2, (18) between the insertions of the first and second fins 18.3, (19) between the end of insertion of the second and beginning of the caudal fins 30.4, (21) between the beginnings of insertions of the ventral and caudal fins 14.7, (22) between the beginnings of insertions of the pectoral and ventral fins 33.5, (23) between the inner corners of nostrils 4.0, (24) width of the mouth 11.6 and lengths of the gill openings: (25) 1st 3.1, (26) 2nd 3.1, (27) 3rd 3.3, (28) 4th 3.1, (29) 5th 3.1; (30) length of spiraculum 0.8, (31) horizontal diameter of the eye 2.0, (32) vertical diameter of the eye 1.0, (34) length of the first dorsal fin 9.8, (36) length of insertion of the first dorsal fin 4.5, (37) length of posterior edge of the first dorsal fin 6.3, (38) depth of the first dorsal fin 3.2, (39) interorbital distance 9.9, (40) total length of the first dorsal fin 9.1, (41) length of insertion of the second dorsal fin 5.7, (42) length of posterior edge of the second dorsal fin 8.3, (43) depth of the second dorsal fin 2.1, (44) length of insertion of the pectoral fin 4.5, (45) length of anterior edge of the pectoral fin 11.6, (46) length of inner edge of the pectoral fin 4.4, (47) length of posterior edge of the pectoral fin 5.9, (48) total length of the ventral fin 7.0, (49) length of insertion of the ventral fin 4.0, (50) length of anterior edge of the ventral fin 7.4, (51) length of posterior edge of the ventral fin 3.6, (54) length of upper lobe of the caudal fin 8.8, (55) length of lower lobe of the caudal fin 12.6, (56) from the posterior-upper edge of the caudal fin to the excision of the posterior edge 7.8, (57) depth of exciJOURNAL OF ICHTHYOLOGY

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sion of the posterior edge of the dorsal fin 1.3, (58) broadness of the body near the pectoral fins 14.7, (59) depth of the body near the pectoral fins 8.3, (60) from the snout to the end of the pectoral fin 38.5, (61) distance between the edges of the mouth 12.9, (62) from the eye to the first gill opening 11.6, (63) length of the caudal keel about 4. Basic meristic characters: dental formula 22 + 1 + 22 = 45 (upper jaw), 25 + 1 + 25 = 51 (lower jaw); number of dentures 4–5 (upper jaw), 2 (lower jaw); turns of the spiral valve 37; it was impossible to determine a number of vertebrae (obviously, in connection with their insufficient calcinations). The shapes of the teeth and dermal denticles are shown in Figs. 2 and 3. The attempt of identification of the shark from the Nazca ridge by the key of Yano and coauthors (2004) indicates, quite without question, its belonging to the subgenus Somniosus (the hook-shaped dermal denticles, skew tops of teeth of the lower jaw, 51 dentures in it, more than 29 turns of the spiral valve). At the same time, our specimen differs well from S. microcephalus by the smaller first predorsal length (less than 45% of TL) and greater number of turns of the spiral valve (37 vs. 29–34) and, from S. pacificus and S. antarcticus, by the greater 1st predorsal length (noticeably more than 45% of TL) and the interdorsal distance evidently inferior to the prebranchial distance in length (in our fish the first predorsal length is about 45% of TL, and the interdorsal distance is commensurable with the length from end of the snout to the first gill slit). The belonging of the shark from the Nazca ridge to the species that is not described yet is possible. REFERENCES 1. N. F. Chirichigno, Clave para identificar los peces marinos del Peru (Inst. Mar. Peru, 1998). 2. L. J. V. Compagno, “FAO Species Catalogue. Sharks of the World. An Annotated and Illustrated Catalogue of the Shark Species Known to Date. Part 1. Hexanchiformes

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PARIN, KOTLYAR to Lamniformes,” FAO Fish. Synop. 4 (135), Part 1, 1– 249 (1984). N. V. Parin, “Preliminary Review of Ichthyofauna of the Nazca and Sala-y-Gomes Submarine Ridges, (the Southeastern Part of the Pacific Ocean),” Tr. Inst. Okeanol. Ross. Akad. Nauk 125, 6–36 (1990). N. V. Parin, K. N. Nesis, and Yu. A. Rudyakov, “Studies of the Fauna of the Nazca and Sala-y-Gomes Submarine Ridges, the Southeastern Part of the Pacific Ocean,” Okeanologiya 28 (6), 1040–1043 (1988). N. V. Parin, “Fish Fauna of the Nazca and Sala-y-Gomes Submarine Ridges, the Easternmost Outpost of the IndoWest Pacific Zoogeographic Region,” Bull. Mar. Sci. 49 (3), 671–683 (1991). N. V. Parin, A. N. Mironov, and K. N. Nesis, “Biology of the Nazca and Sala-y-Gomes Submarine Ridges, an Outpost of the Indo-West Pacific Fauna in the Eastern Pacific

Ocean: Composition and Distribution of the Fauna, Its Communities and History,” Adv. Mar. Biol. 32, 145–242 (1997). 7. G. R. Pequen˜o, J. Lamilla, and A. E. Covetto, “Capture de Somniosus cf. pacificus Bigelow and Schroeder, 1944, frente a Valdivia, Chile, con notas sobre su contenida Gastrico (Chondrichthyes, Squalidae),” Estud. Oceanol. Antofagasta 10, 117–122 (1998). 8. K. Yano, J. D. Stevens, and L. J. V. Compagno, “A Review of the Systematics of the Sleeper Shark Genus Somniosus with Redescriptions of Somniosus (Somniosus) antarcticus and Somniosus (Rhynoscymnus) longus (Squaliformes: Somniosidae),” Ichthyol. Res. 51 (4), 360–373 (2004).

Translated by G.B. Medveshchuk

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