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Aplacophora (Solenogastres; phylum Mollusca, class Amphineura) A subclass of benthic, worm-like molluscs which lack a dorsal covering of valves. Calcareous spicules may occur in the mantle that covers the body. The anatomy and nervous system are very similar to those of the Polyplacophora. The ventral foot is represented as a groove in the order Neomeniida, but is absent in the second order, Chaetodermatida. They are entirely marine, and have a world-wide distribution. This group does not occur in the fossil record.