Author: (Günther, 1877)
Field Marks:
Black coloration, small dorsal fin spines, no anal fin, moderately long snout, small lanceolate teeth without cusplets in upper jaw and large high, knife-cusped cutting teeth in lower jaw, mouth moderately wide and nearly transverse, caudal fin with strong subterminal notch and short lower lobe.
Diagnostic Features:
Head rather low and flat; snout rather narrow and long, preoral length greater than mouth width and almost equal to distance from lower symphysis to first gill slits; mouth fairly narrow, short and transverse; postoral grooves very long, much longer than upper labial furrows; gill slits rather short, longest less than half eye length. Pectoral fins fairly broad and leaf-shaped; apices of pectoral fins falling well in front of first dorsal spine; pelvic fins small, about equal to second dorsal fin; caudal fin with a strong subterminal notch and a short lower lobe. Lateral trunk denticles with cross-ridges on crowns. Caudal peduncle long, distance from second dorsal base to upper caudal origin about equal to second dorsal base.
Geographical Distribution:
Western Pacific: Japan (southeastern Honshu), probably also Kyushu-Palau Ridge; very similar and probably identical dogfish occur in the South China Sea, off southeastern Australia (New South Wales) and New Zealand.
Habitat and Biology:
A little-known deepwater shark of the western Pacific continental slope, down to at least 631 m.
Size:
Maximum total length reported the adult female holotype of about 69 cm; male adult at 49 cm.
Interest to Fisheries: None.
Remarks:
Nakaya (1982) reported a Scymnodon from the Kyushu-Palau Ridge as S. obscurus, because of the presence of transverse ridges on its denticles, said by Bigelow and Schroeder (1957) to differentiate it from S. squamulosus. Although the writer was unable to examinethe holotype of S. squamulosus in the British Museum (Natural History), he examined a very similar adult male Scymnodon, 49 cm long from Japan in the Stanford University collection; this proved to have denticles with transverse ridges like specimens of S. obscurus, and leads the writer to suspect that the holotype of squamulosus has these ridges also. Meanwhile, Chu et al. (1982) reported on Scymnodon material from the South China Sea similar to Nakaya's, but unfortunately named a new species for it, S. niger. The writer has examined similar Scymnodon specimens from New Zealand and Australia that are again similar to the Japanese, Kyushu-Palau Ridge, and South China Sea material, and suspects that all of these specimens may represent a single species, S. squamulosus. If S. squamulosus also has transverse ridges on its denticles, there are apparently no characters to differentiate this species from S. obscurus and hence the two species may be synonyms, as suspected by Krefft (1980).
Type material:
Holotype: British Museum (Natural History), adult female about 690 mm long. Type Locality: Off "Inosima", Japan, 631 m depth.