A predatory use of counterillumination by the squaloid shark, Isistius brasiliensis

A number of very unusual morphological and behavioral characteristics attributed to the cookie-cutter shark, Isistius brasiliensis, may be explained by a novel use of counterillumination. Specifically, it is proposed that a band of pigment, located beneath the jaw and bounded by ventrally directed bioluminescence, acts as a lure which mimics the search image of many upward-looking pelagic predators.