Eyespot rasbora ventral area of the body between the operculum and the pelvic fins (corresponding roughly to the sac enclosing the alimentary canal). Under conditions of reflectied light, the fish sometimes displays a fine lateral band from the opeculum to the end of the caudal peduncle (Walker, 1971, p. 98) this being an olive-gold hue. The fins, with the exception of the dorsal fin, are hyaline, the relation of the pectoral and pelvic fins being typical of the ostariophysans (fishes possessing an auxiliary mechanism for detecting sound consisting of a set of internal bones called the Weberian Ossicles). In such fishes, the
Largetooth cookiecutter shark and sparsely scattered light-emitting photophores on the belly. Most specimens have lacked the dark "collar" found on the throat of "I. brasiliensis". However, a specimen caught in 2004 off the Azores did possess the collar. The maximum recorded length is . Based on its smaller dorsal and caudal fins, the largetooth cookiecutter shark is believed to be less active than "I. brasiliensis" and an overall weak swimmer. Much of its body cavity is occupied by an enormous oil-filled liver, which allows it to maintain neutral buoyancy in the water column with little effort. Unlike "I. brasiliensis", this shark possesses binocular