MOLLUSCS OF BRITISH COLUMBIA

 Class Aplacophora 

(Sclerite-bearing deep sea molluscs)

by

James A. Cosgrove

The Class Aplacophora (a = without, placo = tablet, phoros = bearing) describes a small group of worm-like marine animals that have no shell.  For many years biologists classified the aplacophorans with the sea cucumbers (Phylum Echinodermata) but in 1875 they correctly identified them as a class of the Phylum Mollusca.

Consisting of slightly more than 300 described species, aplacophorans live throughout the oceans of the world.  These small (usually less than 5 cm) animals burrow under muddy sediments.  They move slowly through the mud or on the surface of the mud using cilia.  Some of the members of this class feed on the mud itself and digest the organic portions of the mud.  Other members of this class feed on cnidarians that live on the surface of the mud.

While science has a fundamental knowledge of the physical aspects of this Class such as descriptions of their physical bodies, their development from a larvae, their reproduction, their foods and their habitats, there is still much to be discovered.  Due to their isolation, little is known of their longevity, their communication and defense behaviours and their role in the ecosystem.  

Without question, as scientists obtain new tools provided by technology (such as remotely operated vehicles and small submersibles), more work will be done on the benthic organisms of the deep ocean.  There will be many more aplacophoran species discovered and our understanding of their role in the ecology of the deep ocean will be enhanced.