Bopyridae

Bopyridae
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Subphylum:	Crustacea
Class:	Malacostraca
Order:	Isopoda
Suborder:	Cymothoida
Superfamily:	Bopyroidea
Family:	Bopyridae Rafinesque, 1815
Genera
see text

see text

The Bopyridae are a family of isopod crustaceans in the suborder Cymothoida. Members of the family are ectoparasites of crabs and shrimps. They live in the gill cavities or under the carapace where they cause a noticeable swelling. Fossil crustaceans have occasionally been observed to have a similar characteristic bulge.

...
Wikipedia