six-gilled shark(n = noun.animal) cow shark, hexanchus griseus - large primitive shark widely distributed in warm seas;
is a kind of shark
is a member of genus hexanchus, hexanchus

angel shark, basking shark, blacktip shark, blue shark, bonito shark, bonnet shark, bull shark, card shark, carpet shark, cat shark, cow shark, cub shark, dusky shark, fox shark, great blue shark, great white shark, hammerhead shark, lemon shark, loan shark, mackerel shark, mako shark, man-eating shark, nurse shark, oceanic whitetip shark, reef whitetip shark, requiem shark, sand shark, sandbar shark, shark, shark oil, shark repellent, smoothhound shark, soupfin shark, thresher shark, tiger shark, whale shark, white shark, white-tipped shark, whitetip shark