Glochidium is a name given to the larvae found in the fresh-water mussels of the family Unionidae. In the swan mussel, Anodonta, for example, the eggs undergo development within the body of the mother, between the lamellae of the gills. The young so produced are quite unlike the mother, the valves of the shell having each a sharp incurved tooth. When discharged into the water, the glochidia attach themselves, if possible, to the tail, fins, or gills of a fish by means of the sharp teeth, and become for a time parasitic. Subsequently a metamorphosis occurs: the little bivalve acquires the adult form, and quitting the host, sinks down to the bottom.