Mollusks have well developed body organs that are used in the respiratory, circulatory and nervous systems. The stomach-foots include snails, limpets and abalones, which have shells. Slugs and nudibranchs are also stomach-foots, but do not have shells. A few stomach-foots are found on land. It also has very hard teeth that are also used to scrape algae of rocks.
Chitons are very, very slow moving.
They include Clams, mussels, oysters and scallops. Most bivalves do not have radula because they eat by filtering water through their gills to obtain organic particles. Most bivalves attach themselves to something or burrow underground. Some scallops, however, do not attach themselves to anything and are able to swim by squirting water through their mantle. When an irritant, such as a grain of sand, becomes embedded in the mantle of a bivalve, the creatures coats the irritant with the same material used to produce the lining of its shell.