Morphological Organization of Cerata in the Nudibranch Pteraeolidia semperi (Gastropoda, Nudibranchia).

The morphology of cerata and cnidosacs were studied in the nudibranch mollusk Pteraeolidia semperi (Bergh, 1870). Fine tubules arise from the gastrodermal channel of the digestive gland and contain cells with symbiotic algae (zooxanthellae). The cnidosac stores large kleptocnides. Thus, P. semperi provides a unique example of symbiotrophic feeding specialization. Morphological organization of its cerata and the digestive gland demonstrates several adaptations for housing zooxanthellae and providing them with proper conditions for active photosynthesis.