SHARKS

364 Sharks
6a. Dorsal-fin spines without grooves; teeth similar and blade-like in both jaws, with a deflected
horizontal cusp, a low blade, and no cusplets; caudal peduncle usually with a precaudal pit
(weak or absent in Cirrhigaleus) and always with strong lateral caudal keels; subterminal
notch absent from caudal fin (Fig. 5) . . . . . . . . . . . . . . . . . . . . . . . . Squalidae
6b. Dorsal-fin spines, where present, with lateral grooves; teeth variable but not similarly
blade-like and without a deflected horizontal cusp in both jaws; caudal peduncle without
precaudal pits and usually without lateral keels (weak ones in some dalatiids); subterminal
notch usually present and well developed . . . . . . . . . . . . . . . . . . . . . . . . . 7
7a. Upper teeth with a cusp and lateral cusplets; underside of body usually with more or less
conspicuous dense black markings indicating the presence of numerous light organs
(photophores) (Fig. 6) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Etmopteridae
7b. Upper teeth with a cusp but without lateral cusplets; underside of body without conspicuous
black markings and light organs . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
8a. Upper teeth relatively broad and blade-like, imbricated, lowers low and wide (Fig. 7) . Centrophoridae
8b. Upper teeth relatively narrow and not blade-like, lowers high and wide . . . . . . . . . . . . 9
FIg. 7 Centrophoridae
Fig. 8 Somniosidae
9a. Head moderately broad and somewhat flattened or conical; snout flat and narrowly
rounded to elongate-rounded in dorsoventral view; abdomen usually with lateral ridges;
both dorsal fins with low fin spines in species known from the area (absent in the
extralimital Scymnodalatias and Somniosus) (Fig. 8) . . . . . . . . . . . . . . . . Somniosidae
9b. Head narrow and rounded-conical; snout conical and narrowly rounded to elongate-rounded
in dorsoventral view; abdomen without lateral ridges; dorsal fins usually without
spines (except for a small spine present on the first dorsal fin of Squaliolus) . . . . . Dalatiidae
10a. One dorsal fin, far posterior on back; 6 or 7 gill slits on each side . . . . . . . . . . . . . . 11
10b. Two dorsal fins; 5 gill slits on each side . . . . . . . . . . . . . . . . . . . . . . . . . 12
11a. Six gill slits, with the first connected across the underside of the throat; body elongated and
eel-shaped; teeth tricuspidate and similar in both jaws (Fig. 9) . . . . . . . . Chlamydoselachidae
11b. Six or 7 gill slits, with the first not connected across the underside of the throat; body fairly
stocky, not eel-shaped; anterior teeth unicuspidate in upper jaw and comb-shaped in lower
jaw (Fig. 10) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hexanchidae
6 gill slits
Fig. 9 Chlamydoselachidae
no subterminal notch
strong lateral keels
Fig. 5 Squalidae Fig. 6 Etmopteridae
6or7gill
slits
Fig. 10 Hexanchidae
notch