REPRODUCTION IN ANTHELIA-GLAUCA (OCTOCORALLIA, XENIIDAE) - II - TRANSMISSION OF ALGAL SYMBIONTS DURING PLANULAR BROODING

The soft coral Anthelia glauca Lamarck, 1816, of the family Xeniidae, is found on the reefs of KwaZulu-Natal, South Africa, Its gastrodermal cells contain numerous endosymbiotic unicellular algae (zooxanthellae ). A, glauca is a gonochoric species that simultaneously broods its pl anulae within the pharyngeal cavity of the polyps. Symbiotic algae app ear with zygote formation within the pharynx, embedded in amorphous ma terial. The algal cells adhere to the ciliated ectodermal surface of i mmature planulae and are most probably endocytosed by them. Zooxanthel lae are translocated towards the basal part of the ectoderm. Gaps are subsequently opened in the mesoglea into which symbionts surrounded by ectodermally derived material, including plasma membrane. pass. The b asal membrane of endodermal cells disintegrates, and the algae bulge i nto spaces formed in the underlying endoderm. Throughout the process, each zooxanthella resides within a vacuolar membrane in the detached e ctodermal cytoplasm. The acquisition process is essentially one in whi ch zooxanthellae are translocated from the pharyngeal cavity into the ectoderm and then through the mesoglea into the endoderm, culminating in the final symbiotic state. The direct transmission of symbiotic alg ae to the eggs or larvae probably provides the most efficient means wh ereby zooxanthellae are acquired by the host progeny.