The BR Bank Chinchorro is located in oceanic waters of the Mexican Caribbean, has atoll form, and it is separated from the coast of Quintana Roo for a channel of 1000 m of depth. It possesses four islands: two to the north, one in the middle and the smallest in the south. It possesses great habitat variety that includes: a shallow reef lagoon of 840 area km2 with patches (microatolones) disseminated along its extent, coralline formations very developed in the south part, and very abrupt slopes that exceed 500 In. The central island (Cayo Centro) has a network of mangrove islands has originated a lagoon microsystem connected by small, shallow channels. The unusual discovery of a population of Isognomon alatus in an internal channel of approximately 100 m of longitude in Cayo Centro, propted an investigation of the environmental conditions that supported that unusual establishment. Bimonthly observations were undertaken from February to November in 1998, to define the environmental parameters taking into account 12 parameters of the atmosphere and correlating the weight, the longitude, and the width of the shell. The half part of the channel was that of more abundance and the initial part that of smaller abundance. The regressions between the weight and the other morphometric parameters were greater in the half part reaching correlation coefficients greater than 0.8. In relation to the different parameters, most presented lower values in the final part of the channel. This paper demostrates how each environmental parameter influences the populational variability of this mollusk.