Marine annelid worms have larvae called trochophores that swim about by means of cilia. Many mollusks, including clams, oysters, scallops, snails, and periwinkles, have a free-swimming larva called a veliger. Some also have another larval stage, a trochophore similar to that of the annelids. The larvae of freshwater mussels, called glochidia, fasten themselves to the gills or skin of fishes and ride about on them. Then they drop off and burrow in the bottom.
Barnacles have distinct larval stages called nauplii and cyprids.
These larvae swim and drift great distances before fastening themselves to solid objects and becoming adults. Larvae of many water animals are important food for fishes. Most insects have larvae more or less distinct from the adults. Larvae that undergo incomplete metamorphosis change directly to the adult stage. Such larvae are often called naiads if they belong to water insects.