Coral reefs are considered the most diverse and pro-ductive ecosystems on the planet (Levinton 1982).Symbiotic interactions between phylogenetically unre-lated organisms play a very important role in coral reefecology (Carrera-Parra and Vargas-Herna´ndez 1997),and stony corals host many organisms that live on theirsurface or within their skeletons (Abelson et al. 1991).Crabs are commonly associated with corals and may betotally dependent on coral for protection against pre-dators, or as a food source either from coral mucus ortrapped particulate material (Patton 1974; Castro 1976;Rinkevich et al. 1991). Cryptochiridae, or gall crabs asthey are commonly known, are obligate symbionts ofstony corals. These crabs can modify coral morphologyby affecting growth (Simon-Blecher and Achituv 1997;Simon-Blecher et al. 1999). This, in turn, can alter localwater flux and thus the movement of suspended partic-ulate food (Abelson et al. 1991). Two forms of growthmodification have been observed: depressions, called‘‘pits,’’ in massive corals, and flattened spheres, called‘‘galls,’’ made of two valves in branching corals. Thesetwo forms of coral growth modification are associatedwith the alimentary mechanisms of the crabs. Thosefeeders that form pits obtain food from materialdeposited in the depression while those that form gallsare suspension feeders (Abelson et al. 1991).In this note we present ecological and ethologicaldata for Troglocarcinus corallicola Verrill, one of the twoknown species of gall crabs in the Mexican Atlanticwhich lives in symbiosis with the host stony coral,Manicina areolata Linnaeus. Troglocarcinus corallicolaoccurs throughout the Atlantic and is the most widelydistributed of the Atlantic cryptochirids. In the westernAtlantic, this species has been recorded in Bermuda andlocalities from southeastern Florida to Brazil. In theGulf of Mexico it has been previously found in Barra delTordo, Tamaulipas, and in the Veracruz Reef System,Veracruz. The species has been reported as a symbiontof several species of stony corals, including M. areolata(Kropp and Manning 1987).