Moss animals are actually colonies of very small and independent individuals that are only about 1 mm long.  There are over 300 species of moss animals (bryozoans) that live in the coastal waters of the Pacific Northwest.  These colonies can have a flat shape that clings to the rock surface, or a branching upright structure, and finally they may also be flexible in nature.   The individual zooids that make up a colony each secrete calcium carbonate making a protective structure in which they live.  The zooid partially extends out of its home revealing a crown of tentacles to the surrounding water for feeding.