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Author: Springer and Waller, 1969

Field Marks:
A slender-bodied, narrow-headed sixgill shark, mouth ventral with 5 rows of lower bladelike, comb-shaped teeth on each side, one dorsal fin.

Diagnostic Features:
Body rather slender; size moderate, up to 1.8 m long. Head narrow and pointed; eyes large; lower jaw with 5 rows of large, comblike teeth on each side, these with relatively long cusps. Caudal peduncle long and slender, distance from dorsal fin insertion to upper caudal origin at least twice length of dorsal fin base.

Geographical Distribution:
Widely but spottily distributed in warm temperate and tropical seas; in the western North Atlantic: off the Bahamas, northern Cuba, Nicaragua, and Costa Rica; eastern Atlantic: off Gibraltar and possibly Ivory Coast and Nigeria; Indian Ocean: off southern Africa, Aldabra Island (India), Madagascar and Kenya; western Pacific, off Taiwan Island and the Philippines (Luzon).

Habitat and Biology:
Continental and insular shelves and slopes from 90 to 600 m depth, usually on or near bottom, but occasionally at the surface in the tropics.

A little-known, primarily deepwater shark. Ovoviviparous, number of young 13 in one litter. Eats small to medium-sized fishes, and probably bottom invertebrates. Not dangerous to people as far as is known.

Size:
Maximum tatal length about 180 cm, length at birth about 43 cm, females mature at 142 to 178 cm, males at 123 to 157 cm.

Interest to Fisheries:
Apparently uncommonly taken on line gear and in trawls and of relatively slight importance to fisheries.

Remarks:
Specimens of this species were listed and illustrated as H. griseus by Nakamura (1936, pl. 1, fig. 1) from Taiwan Island. Teng (1962) described a new Taiwanese subspecies, H. griseus nakamurai, based on two specimens from Keelung: Taiwan Fisheries Research Institute No. 2515, 750 mm juvenile male, designated as its holotype, and no. 3280, 970 mm female, designated as paratype. Teng also described and illustrated typical H. griseus from Taiwan as H. g. griseus. Springer and Waller (1969) described the new H. vitulus but failed to mention Nakamura's and Teng's earlier accounts.

Comparison of the original descriptions of H. griseus nakamurai and of H. vitulus strongly suggests that the two are synonyms. I retain H. vitulus because the question exists as to whether Teng's (1962) work was actually published and if his names are available. It has beencited as a publication by Chen (1963) and Springer (1979), but may be an unpublished Ph.D thesis (Dr S.C. Shen, pers.comm. to Dr P.C. Heemstra). Chen (1963:1) stated that "Hexanchus griseus nakamurai n.subsp." was a synonym of H. griseus, and under that species (p. 6) listed nakamurai as a synonym. If Teng's name is not available from his 1962 monograph, it is an open question whether its citation in Chen establishes it beyond the status of nomen nudum.

Type material:
Holotype: U.S. National Museum of Natural History, USNM 200674, 148 cm adult male caught off Bimini, Bahamas, in about350 m depth.

Bigeyed sixgill shark (Hexanchus vitulus)