The organization of the zooxanthellate scleractinian coral Leptoseris fragilis was studied. The architecture of the corallite and the histology of the polyparium were analysed for adaptations that enable efficient capture and retention of suspended particles which would increase energy supply. The data indicate that the gastrovascular system of L. fragilis is not a blind but a flow through system. Water entering the coelenteron through the mouth leaves the body not only through the mouth but also through microscopic pores (≂ 1–2 μm) which are located near the crests of the sclerosepta in the oral epithelia. Irrigation is achieved by flagellar and probably also by muscular activity. This type of filtration enables L. fragilis, which lacks tentacles, to utilize suspended organic material including bacteria. The supposed suspension feeding in combination with effective photoadaptations (presented in former communications) seems to be the basis for the survival of L. fragilis in an extreme habitat (between-95 and-145 m) and for its, successful competition with other scleractinian species provided with larger catching surfaces, and with other invertebrates depending on filter feeding.