cross-posted from: https://lemmygrad.ml/post/4533434

The cookiecutter shark, also called the cigar shark, is a species of small squaliform shark in the family Dalatiidae. This shark occurs in warm, oceanic waters worldwide, particularly near islands, and has been recorded as deep as 3.7 km. This small, cigar-shaped shark is dark brown on top and light on the underside, with a darker band around its neck. The light underside glows, attracting fish, whales, and sharks. It attaches itself to the prey and uses its serrated bottom teeth to cut out a perfectly circular chunk of flesh. Cookiecutter sharks are poor swimmers, and generally only caught at night. They probably migrate vertically from deep water [2000-3000 m] to midwater or surface at night. They are an ectoparasite on large fish and cetaceans, which are possibly lured to the shark by its bioluminescent light organs. Cookiecutter sharks live in the warm, deep waters of equatorial oceans, primarily in coastal waters near islands. They inhabit deep waters below 1,000 m during the day and migrate into surface waters at night at around 300 m. They eat smaller animals (like squid) whole, but also take large, round cookie-cutter shaped bites out of larger animals, such as tuna, whales, dolphins, and seals. Potential predators of the cookiecutter shark include large sharks and bony fish. The cookiecutter shark is ovoviviparous, meaning it gives birth to live pups after they develop inside egg cases within the uterus of the mother. Each developing pup feeds off the yolk inside the egg case, remaining there until it is fully developed. Like all sharks, cookiecutter sharks lose several sets of teeth throughout their lifetimes. This process ensures that they always have sharp, healthy teeth capable of feeding by their preferred strategy. Unlike other species, though, cookiecutter sharks apparently purposely swallow the teeth that they lose.