Echinoecus is a genus of crabs that live in association with sea urchins. Formerly considered monotypic, the genus is now thought to contain three species: \n* Echinoecus nipponicus Miyake, 1939 – Japan, on Heliocidaris crassispina (Echinometridae) and Pseudocentrotus depressus (Strongylocentrotidae) \n* Echinoecus pentagonus (A. Milne-Edwards, 1879) – East Africa and Red Sea to Hawaii and French Polynesia, on Diadema savignyi, D. setosum, Echinothrix calamaris and E. diadema (Diadematidae), Heterocentrotus mammillatus (Echinometridae) and Pseudocentrotus depressus (Strongylocentrotidae) \n* Echinoecus sculptus (Ward, 1934) – Christmas Island, on Colobocentrotus atratus (Echinometridae)