Solenogaster

Solenogasters are worm-like, shell-less marine mollusks belonging to the class Aplacophora, found on the sea floor worldwide, most commonly in deep water, where many species feed on cnidarians such as corals and hydroids. Their bodies are covered not by a shell but by tiny calcareous spicules embedded in the skin, and their close evolutionary relationship to shelled mollusks has made them significant to scientific understanding of how the ancestral mollusk body plan first evolved.