Echinoecus pentagonus

The "sea urchin crab" ''Echinoecus pentagonus'' is a species of crab in the family Pilumnidae found from the Red Sea and East Africa to French Polynesia and the Hawaiian Islands. This crab is a parasite that lives in the rectum of a sea urchin. In Hawaii, it chooses only ''Echinothrix calamaris'', leaving few of these urchins unpopulated. Its curved and pointed carapace reaches only 0.5 inches in width.

Taxonomic synonyms of ''E. pentagonus'' include:
*''Echinoecus klunzingeri'' Miyake, 1939
*''Echinoecus pentagonus'' Rathbun, 1894
*''Echinoecus rathbunae'' Miyake, 1939
*''Eumedon convictor'' Bouvier & Seurat, 1906
*''Eumedon pentagonus'' A. Milne-Edwards, 1879
*''Eumedonus petiti'' Gravier, 1922
*''Liomedon pentagonus'' Klunzinger, 1906