The snub-nose eel, Simenchelys parasitica, is a small deep-sea eel, about 20 to 35 centimetres long. It has attracted note by being found a number of times burrowed into the body cavity of larger fishes with perhaps the most renowned case being two juveniles that were found nested inside the heart of a mako shark. This lead to the description of S. parasitica as an endoparasite (hence the species name). However, acceptance of this tag has been far from universal. The snub-nosed eel has been caught free-living more regularly than it has been found in other fish.