Aplacophora is a class of small wormlike marine animals. For a long time they were a mystery to marine biologists: up until 1987 they were classified as sea cucumbers (which are echinoderms). However the shell-free Aplacophorans are not echinoderms at all, no more than penguins are insects. Aplacophorans are tubular and lack shells, but they are actually mollusks—like clams, belemnites, octoposes, and gastropods.
Aplacophorans are divided into two subclasses: (1) the Solenogasters, which are typically carnivores which feed on feeding on corals and worms; and (2) the caudofoveates which tend to be detritovores feeding on leftover bits rolling around the ocean floor (although some caudofoveates eat foraminiferans (which are large unicellular organisms).
All of this talk of small mollusks which look like little worms…or maybe like little echinoderms…or even possibly like little early chordates (which were basically little tubes) sounds unpromising, but some of the Aplacophorans have a subtle beauty. Additionally they throw a light upon a bygone time when the mollusks, cnidarians, sponges, worms, and proto-vertebrates really weren’t all that different. They help illustrate the common bonds of kinship which tie all of the animals together, no matter what airs some of us put on.