Cookie Cutter Shark
The Cookie-cutter Shark is named after the cookie-shaped wounds that it leaves on the bodies of larger animals. This species has a small cigar-shaped body (up to about 50 cm in length), a conical snout and two low, spineless dorsal fins positioned posteriorly on the body. It is dark brown dorsally, lighter below, and has a distinct dark collar around the gill region (visible in the middle image). The entire ventral surface, with the exception of the dark collar, is covered in a dense network of tiny photosphore, which in life produce an even greenish glow. The genus name Isistius is derived from Isis, the Egyptian goddess of light.
This species has small, erect teeth in the upper jaw and large triangular teeth in the lower jaw. The Cookie-cutter Shark attaches itself to its prey with its suctorial lips, and then spins to cut out a cookie-shaped plug of flesh from the larger animal.