<P> Marine mussels are usually found clumping together on wave - washed rocks, each attached to the rock by its byssus . The clumping habit helps hold the mussels firm against the force of the waves . At low tide mussels in the middle of a clump will undergo less water loss because of water capture by the other mussels . </P> <P> Both marine and freshwater mussels are gonochoristic, with separate male and female individuals . In marine mussels, fertilization occurs outside the body, with a larval stage that drifts for three weeks to six months, before settling on a hard surface as a young mussel . There, it is capable of moving slowly by means of attaching and detaching byssal threads to attain a better life position . </P> <P> Freshwater mussels reproduce sexually . Sperm is released by the male directly into the water and enters the female via the incurrent siphon . After fertilization, the eggs develop into a larval stage called a glochidium (plural glochidia), which temporarily parasitizes fish, attaching themselves to the fish's fins or gills . Prior to their release, the glochidia grow in the gills of the female mussel where they are constantly flushed with oxygen - rich water . In some species, release occurs when a fish attempts to attack the mussel's minnow or other mantle flaps shaped like prey; an example of aggressive mimicry . </P> <P> Glochidia are generally species - specific, and will only live if they find the correct fish host . Once the larval mussels attach to the fish, the fish body reacts to cover them with cells forming a cyst, where the glochidia remain for two to five weeks (depending on temperature). They grow, break free from the host, and drop to the bottom of the water to begin an independent life . </P>

How does an oyster break down its food