Glochidia

the parasitic larvae of freshwater bottom mollusks—Lamellibranchia—of the family Unionidae. Glochidia have bivalve triangular shells, which close by means of single, contracting muscles. The edge of each valve usually has a serrated spine. The foot is undeveloped and is equipped with a long adhesive byssal thread—the lasso. The intestines are reduced. In the early stages of their development glochidia enter the, gills of a host specimen, where they lay eggs. In the spring, with the aid of the spines and the lasso, they attach themselves to the gills and skin of fish. In this manner glochidia spread through a body of water and move against river currents. After metamorphosis, the mollusk drops to the bottom. Glochidia cause no particular damage to fish.