Author: Herre, 1923
Field Marks:
Slender houndsharks with rather long, parabolic snouts, dorsolateral eyes and strong subocular ridges, arched mouths, short anterior nasal flaps, small, wide-set nostrils, differentiated medial and bladelike anteroposterior teeth in both jaws, and second dorsal nearly as large as first.
Diagnostic Features:
Snout moderately long and parabolic dorsoventral view, preoral length less than 1.3 times the mouth width; eyes horizontally elongated and dorsolateral, subocular ridges strong; anterior nasal flaps moderately elongated and lobate, well separated from each other and mouth; no nasoral grooves; internarial width about 2.5 to 2.8 times the nostril width; mouth broadly arched and moderately long; labial furrows moderately long, uppers nearly or quite reaching level of upper symphysis; teeth bladelike, compressed, cuspidate, and similar in both jaws, anteroposteriors with oblique cusps and cusplets; medial teeth well differentiated from anteroposteriors. First dorsal fin moderately large, its base less than 2/3 of dorsal caudal margin; its origin over pectoral inner margins or slightly behind their free rear tips, its midbase about equidistant between pectoral and pelvic bases or closer to pectoral bases; second dorsal nearly as large as first, height about 3/4 as high as first; anal fin considerably smaller than second dorsal; ventral caudal lobe hardly developed in young but short and strong in adults; terminal lobe of caudal fin moderately long and about 2.6 to 2.8 times in dorsal caudal margin.
Remarks:
This genus was revived and revised by Compagno (1970, 1979). Previously Hemitriakis and H. leucoperiptera had been included in Triakis by Fowler (1941), which was followed by various writers. However, H. japanica had been placed in the genus Galeorhinus or its synonyms.
There may be a third species of Hemitriakis in Philippine waters, sympatric with H. leucopteriptera, but differing from it in coloration and fin proportions (Compagno, 1970, 1979). Additionally, a Hemitriakis very like H. leucoperiptera in shape but differing in having higher vertebral counts like H. japanica has been collected off northwestern Australia. This may be identical to leucopteriptera or new, but is certainly not H. japanica.