Notoscopelus caudispinosus anal fin and 11 to 13 in the pectoral fins. There are groups of photophores (small light organs) on the head and sides of the body. Above the caudal peduncle there is a row of eight to nine luminous scale-like segments in adult males, but male fish lack luminous organs above the eye and on the cheek. "N. caudispinosus" differs from closely related species in having fewer than 15 gill rakers. This species has a wide oceanic distribution in deep water habitats. It is found in the eastern Atlantic Ocean between the equator and about 35°N, but is absent from
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