Inc. Sexual reproduction in the tropical corallimorpharian Rhodactis rhodostoma Nanette E. Chadwick-Furman, Michael Spiegel, and Ilana Nir Interuniversity Institute for Marine Science, P.O. Box 469, Eilat, Israel Faculty of Life Sciences, Bar Ilan University, Ramat Gan, Israel Abstract. Polyps of the tropical corallimorpharian Rhodactis rhodostoma segregate sexes between center and edge positions within aggregations produced by clonal replication. On a reef flat at Eilat, northern Red Sea, infertile polyps and males occur mainly along the edges of clonal aggregations, while females mostly occupy central positions within each aggregation. In addition, on the inner to middle reef flat where polyps of this species are abundant, aggregations consist mostly of females. On the outer reef flat, where polyps are rare, a sampled aggregation consisted mostly of males and infertile polyps.
Male polyps are significantly smaller than females, and the smallest polyps are infertile.
Fecundity increases significantly with polyp size in females, but testis size and number do not vary with body size in males. Oocytes are present in polyps during most of the year and gradually increase in size until annual spawning in June-July during the period of maximum day length. The annual spawning of gametes coincides with a temporary drop in the frequency of clonal replication by polyps. The high investment of this corallimorpharian in sexual production of planktonic propagules may allow rapid dispersal to reef habitats distant from parent populations. Evidence for classical neurotransmitters in sea anemones remains controversial.