The family

Family (biology)

In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

 Argulidae contains the carp lice or fish lice – a group of parasitic crustacean

Crustacean

Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...

s of uncertain position within the Maxillopoda

Maxillopoda

Maxillopoda is a diverse class of crustaceans including barnacles, copepods and a number of related animals. It does not appear to be a monophyletic group, and no single character unites all the members.-Description:...

. Although they are thought to be primitive

Primitive

Primitive may refer to:* Anarcho-primitivism, an anarchist critique of the origins and progress of civilization* Primitive culture, one that lacks major signs of economic development or modernity...

 forms, they have no fossil record. Argulidae is the only family in the order

Order (biology)

In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...

 Arguloida (occasionally "Arguloidea"), although a second family, Dipteropeltidae, has been proposed.
Fish lice vary in size from just a few millimetres to over 30 millimetres (1.2 in) long, with females usually somewhat larger than the males.