Abstract: Distribution patterns of some benthic animals showed a close relation with the occurrence of seagrass species in Haad Cai Mai National Park, southern Thailand. At subtidal sites an infaunal bivalve, Pinna bicolor, was present in higher density in Enhalus acoroides beds than in beds of other seagrasses and on bare sand bottoms. While all individuals of the bivalve in Enhalus patches exposed the posterior half of their shells, those in adjacent bare bottom areas exposed just the posterior edge of their shells. At an intertidal site an ocypodid crab, Macrophthalmus quadratus, occurred only in Halophila ovalis beds, and not in unvegetated areas such as bare sand bottoms and dugong feeding trails. In addition, small juveniles of another ocypodid, Uca vocans hesperiae, which occupied burrows, were abundantly seen in Halophila beds. These juveniles had a green body color matching the surrounding Halophila leaves, while individuals of the same species in unvegetated areas had grayish-blue bodies. The relationships between the life-modes of these benthic animals and the structure of their habitats provided by seagrass species are discussed.