Chitons are a small class of marine molluscs, characterised by their possession of 8 dorsal shell plates usually held in place by a leathery girdle. They are bilaterally symmetrical and are usually found on hard intertidal or shallow water surfaces. In some groups however, the shell plates become reduced in size, and are often embedded in the girdle which becomes more fleshy and in some cases brightly coloured. Chitons are grazing herbivores, found in all parts of the world. They range in size from the huge Californian Cryptochiton stelleri, which grows to 300mm in length, to some that never grow more than a few millimeters in length. Rudman, W.B., 2002 (November 24) Chitons, Amphineura and Polyplacophora. [In] Sea Slug Forum
Hermit crabs are decapod crustaceans of the superfamily Paguroidea. Most of the 1100 species possess an asymmetrical abdomen which is concealed in an empty gastropod shell that is carried around by the hermit crab. Wikipedia
Images from Fitzgerald Marine Reserve.