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We studied the distributional ecology of the anemone shrimp Periclimenes rathbunae associating with the anemone Stichodactyla helianthus in Tobago, West Indies. The shrimps occupied 83.1% of the anemones (n = 83), with mean densities of 2.8 shrimps per anemone in the population and 3.4 shrimps per occupied anemone, and up to 11 inhabiting a single anemone. Shrimp density was significantly correlated with anemone size. Because the density of shrimps was not significantly correlated with the distance to the nearest neighboring anemone or the number of anemones in a cluster, colonization appears to be related to chance or some unknown factor rather than degree of isolation. The significantly negative correlation between density and mean size class of shrimps suggests that adult shrimps may limit juveniles from colonizing an anemone. The high frequency of cohabitation between P. rathbunae and other decapod crustaceans, coupled with the lack of correlation between density of P. rathbunae and the number of individuals or species of other decapod crustaceans, suggests that the density of P. rathbunae was unaffected by interspecific competition.