THE GYMNOSOMATA (GASTROPODA , OPISTHOBRANCHIA) IN THE PLANKTON OF THEFRENCH MEDITERRANEAN COAST

During plankton investigations on the French coast at Banyuls-sur-Mer and Villefranche-sur-Mer in the years 1989-1995 six out of ten species of Gymnosomata (Gastropoda, Opisthobranchia) recorded for the Mediter ranean were found, i.e. Pneumoderma atlanticum, Pneumodermopsis caneph ora, P. ciliata, P. paudicens, Cliopsis krohnii and Paraclione longica udata. Specimens in different developmental stages (polytrochous larva e, transitory stages and adults) could be identified by their main ide ntification characters, i.e. protruded prehensile organs such as sucke rarms, proboscis or buccal cones. The species found in the samples are presented in an identification key with clear figures and description s based on light and scanning electron microscopical investigations ar e provided. SEM is used for the first time to study pneumodermatid suc kers.