Answer: (2)
The glochidium or plural glochidia is a microscopic larval stage of some freshwater mussels, aquatic bivalve molluscs in the families Margaritiferidae, and Unionidae.
This larva form has hooks that allow it to bind to fish for a time until it detaches and falls to the substrate and assumes the typical form of a juvenile mussel. Owing to the fact that a fish is active and free-swimming, this cycle helps to disperse the species of mussels to new habitat areas that it could not enter otherwise.
