Lamprey

Lamprey, primitive fish of the Petromyzontidae family, one of the 2 remaining groups of jawless fish (Agnatha), found both in freshwater and in the sea. Its body is eellike, and its round, sucking mouth has horny teeth with which it rasps away at its prey. Many species are parasitic when adult, feeding on the flesh of living fishes. The blind, wormlike, filter-feeding larva is totally unlike the adult.