IMPACT OF BACTERIAL EPIBIOSIS ON FUNCTION AL-MORPHOLOGY OF SHRIMP ASSOCIATED WITH THE MID-ATLANTIC HYDROTHERMAL CONDITIONS

This study deals with a morphological comparison between two carid spe cies, Rimicaris exoculata and Chorocaris chacei, living with a rich ba cterian epibiosis of the mid-Atlantic vents and a third one, Alvinocar is markensis which have no bacteria. On these two species, filamentous bacteria are dominant and fixed on different protected places (inner sheet of carapace : epimera and setae of gnathal appendages). All thes e sites are located on the way of current water which run along a preb ranchial chamber constituted by anterior and lateral expansion of cara pace. In this ''culture chamber'', autotrophic bacteria found favourab le conditions : numerous anchoring points, particularly on setules of setae and on epimera, iron sulfur brought by currents of water and use d of their metabolism. A comparated study of gnathal appendices as als o the reduction of the mouth area and mandibles show that Rimicaris is more modified than Chorocaris. Studies have also been done on interna l gastric armature, digestive contents and gills. Observations of bact eria on integument show that they are on epicuticle. The disappearance of the procuticle at the level of epimera under which exist important hemolym lacunae in Rimicaris suggest a possible direct transcuticle a bsorption of dissolved substances which will be a complementary part s upply to a particular absorption of episymbiotic and free bacteria. Th is bacterian cuticular episymbiosis of the prawns of Atlantic vents re calls that observed for the Pompeii worms from the Pacific, particular ly the carapace which would act a part of the tube.