Glochidium

As Glochidium is called the of fish parasitic larva of families river and pond mussels (Unionidae) and freshwater pearl mussel (Margaritiferidae) in order Unionida . The eggs fertilized in the gills of female mussels (e.g. the great pond mussel ) grow into glochidia in marsupia . These are anchored to the shell flaps with hooks and adhesive threads. After a while they settle into the open water by moving their shell around. The glochidia then attach themselves to a fish, where they live parasitically for two to three months in the gills or on the fins of their host. There they develop and then fall to the ground. Only then do they develop into a filtering mussel.

Web links

Glochidia: larvae of freshwater mussels
Development of Fresh Water Mussels ( Memento from December 2, 2010 in the Internet Archive )