Fish lice

Fish lice are the family Argulidae, or 'carp lice'. They are a group of parasitic crustaceans in the class Maxillopoda.

Fish lice
Argulus sp. on a stickleback
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Subphylum:	Crustacea
Class:	Maxillopoda
Subclass:	Branchiura
Order:	Arguloida Yamaguti, 1963
Family:	Argulidae Leach, 1819

Although they are thought to be primitive forms, they have no fossil record. Argulidae is the only family in the order Arguloida (occasionally "Arguloidea"),^[1] although a second family, Dipteropeltidae, has been proposed.^[2]