Clausidium

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 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 and Upogebiidae, or from water collected from their burrows. Clausidium adhere tenaciously to the host, moving easily over the surface, appendages and into the gill chamber. They are occasionally observed swimming free of the host; however, this behavior is uncommon. The relationship between Clausidium and its host has not been definitively characterized, but may be commensalism.