''Clausidium'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

copepod Copepods (; meaning "oar-feet") are a group of small crustaceans found in nearly every freshwater and saltwater habitat (ecology), habitat. Some species are planktonic (inhabiting sea waters), some are benthos, benthic (living on the ocean floor) ...

s that have been found in subtopical to temperate coastal areas along the Pacific, Atlantic and Gulf coasts of North America, the Pacific and Atlantic Coasts of South America, the Atlantic and Mediterranean coasts of Europe, the Atlantic coast of Africa, and the coast of India. All of the known species occur on the bodies of mud shrimp (a.k.a. ghost shrimp) of the families

Callianassidae Callianassidae is a family of ghost shrimp of the order Decapoda. Subfamilies and genera ''Callianassidae'' is divided into 41 genera: * '' Aqaballianassa'' Poore, Dworschak, Robles, Mantelatto & Felder, 2019 * '' Arenallianassa'' Poore, Dwors ...

and

Upogebiidae Upogebiidae is a family of mud shrimp crustaceans belonging to the infraorder Gebiidea Gebiidea is an infraorder of decapod crustaceans. Gebiidea and Axiidea are divergent infraoders of the former infraorder Thalassinidea. These infraorder ...

, or from water collected from their burrows. ''Clausidium'' adhere tenaciously to the host, moving easily over the surface, appendages and into the gill chamber.Gooding, Richard U. (1963). External morphology and classification of marine poecilostome copepods belonging to the families Clausidiidae, Clausiidae, Nereicolidae, Eunicicolidae, Synaptiphilidae, Catiniidae, Anomopsyllidae, and Echiurophilidae. Ph.D. Thesis, University of Washington, Seattle. pp. 1-247. They are occasionally observed swimming free of the host; however, this behavior is uncommon.Hayes, Howard J. (1984). Biology of ''Clausidium dissimile'': an epizoic copepod. M.Sc. Thesis, University of West Florida, Pensacola, Florida, U.S.A. The relationship between Clausidium and its host has not been definitively characterized, but may be

commensalism Commensalism is a long-term biological interaction (symbiosis) in which members of one species gain benefits while those of the other species neither benefit nor are harmed. This is in contrast with mutualism, in which both organisms benefit fro ...

. The adult male is much smaller than the adult female and is usually found firmly grasping the anal segment of the female. Morphologically the genus is very homogeneous. The unique identifying features seem correlated with the two behaviors of adhesion to the host and the male prehension on the female. The endopod of leg 1 is thick and modified with suckers. Leg 1 of the female also has a distinct large blade-like seta. Partial suckers are on the endopods of legs 2 through 4. Folds and projections on the anal segment of the female apparently complement the structure of the male maxilliped. ''Clausidium'' contains the following species: *''

Clausidium apodiformis ''Clausidium'' is a genus of copepods that have been found in subtopical to temperate coastal areas along the Pacific, Atlantic and Gulf coasts of North America, the Pacific and Atlantic Coasts of South America, the Atlantic and Mediterranean co ...

'' (Philippi, 1839) *'' Clausidium californiense'' C. B. Wilson, 1935 *'' Clausidium caudatum'' (Say, 1818) *'' Clausidium chelatum'' Pillai, 1959 *''

Clausidium dissimile ''Clausidium dissimile'' is a species of copepod that has been found along the Atlantic and Gulf Coasts from Massachusetts to Florida. They are found on the bodies of mud shrimp (a.k.a. ghost shrimp) of the family Callianassidae, or from water ...

'' C. B. Wilson, 1921 *'' Clausidium rodriguesi'' Kihara, and Rocha 2013 *'' Clausidium saldanhae'' Kensley, 1974 *'' Clausidium searsi'' C. B. Wilson, 1937 *'' Clausidium senegalense'' Humes, 1957 *'' Clausidium tenax'' Humes, 1949 *''

Clausidium testudo ''Clausidium'' is a genus of copepods that have been found in subtopical to temperate coastal areas along the Pacific, Atlantic and Gulf coasts of North America, the Pacific and Atlantic Coasts of South America, the Atlantic and Mediterranean co ...

'' Kossmann, 1867 *''

Clausidium travancorense ''Clausidium'' is a genus of copepods that have been found in subtopical to temperate coastal areas along the Pacific, Atlantic and Gulf coasts of North America, the Pacific and Atlantic Coasts of South America, the Atlantic and Mediterranean co ...

'' Pillai, 1959 *''

Clausidium vancouverense ''Clausidium vancouverense'', the red copepod, is a symbiont of the ghost shrimp ''Neotrypaea californiensis''. It is one of six species in the genus '' Clausidium'' and is found with its host in the Pacific Ocean from Alaska to Baja Californi ...

'' (Haddon, 1912)

References

Poecilostomatoida {{copepod-stub