Diversity and ecological remarks of ectocommensals and ectoparasites (Annelida, Crustacea, Mollusca) of echinoids (Echinoidea: Mellitidae) in the Sea of Cortez, Mexico.

The diversity of symbiotic invertebrates on intertidal and shallow water echinoids of the northwestern Gulf of California was studied. Five ectosymbionts were found: three pinnotherid crabs, Dissodactylus lockingtoni Glassell (1935), Dissodactylus nitidus Smith (1870), and Dissodactylus xanthusi Glassell (1936); one eulimid gastropod, Turveria encopendema Berry (1956); and one polychaete, Struwela sp. We discovered seasonal fluctuation in D. nitidus Smith (1870) and D. xanthusi Glassell (1936), which result in these species being undetectable during the winter season when the temperature in the head of the Gulf of California drops to 14-18 degrees C; the rest of the species are permanent residents in this area. An updated list of all external macrosymbionts of echinoids of the Mexican Pacific is presented.