SYMBIOSIS BETWEEN METHANE-OXIDIZING BACTERIA AND A DEEP-SEA CARNIVOROUS CLADORHIZID SPONGE

Dense bush-like clumps of several hundred individuals of a new species of Cladorhiza (Demospongiae, Poecilosclerida) were observed near meth ane sources in mud volcanoes, 4718 to 4943 m deep in the Barbados Tren ch. The sponge tissue contains 2 main morphological types of extracell ular symbiotic bacteria: small rod-shaped cells and larger coccoid cel ls with stacked membranes. Stable carbon isotope values, the presence of methanol dehydrogenase and ultrastructural observations all indicat e that at least some of the symbionts are methanotrophic. Ultrastructu ral evidence of intracellular digestion of the symbionts and the stabl e C and N values suggest that the sponge obtains a significant portion of its nutrition from the symbionts. Ultrastructure of the sponge emb ryo suggests direct transmission through generations in brooded embryo s. The sponge also maintains a carnivorous feeding habit on tiny swimm ing prey, as do other cladorhizids.