Slit Shell

Slit shells are large sea snails of the family Pleurotomariidae, named for a distinctive slit along the outer edge of the shell that vents water and waste from the gills as the animal grows. The family has an ancient fossil record stretching back hundreds of millions of years, with a great diversity of extinct forms known mostly from Paleozoic rocks, so living slit shells are often described as living fossils. Today's species live in deep water on the outer edges of reefs and continental shelves, mostly in the tropics, and are rarely seen alive because of the depths they inhabit.