Aplacophora

The Aplacophora is a class of small, deep-water, exclusively benthic, shell-less marine molluscs. They are found in all oceans of the world. They are a small group of molluscs which have deviated from the normal molluscan form. There are approximately 100 known species living today. They are rather worm-like and average about an inch (2.5 cms.) in length.
Description.
Most live in deep water, except a few more northern species. One group bury themselves into the sand and mud of the ocean bottom where they feed on annelids and other small invertebrates. The rest of the known aplacophorans parasitize hydroids and other corals.
This class used to be classified as sea cucumbers in the echinoderms. In 1987, they were officially recognized as molluscs and given their own class. The class is polyphyletic, and consists of two clades.