Symbiosis between Symbiodinium (Dinophyceae) and various taxa of Nudibranchia (Mollusca: Gastropoda), with analyses of long-term retention

Long-term retention of zooxanthellae in five different species belonging to two different nudibranch groups (Aeolidoidea and Dendronotoidea) was investigated. Specimens belonging to the species Phyllodesmium briareum, Phyllodesmium colemani, Phyllodesmium longicirrum, Pteraeolidia ianthina and Melibe engeli were cultivated for 70–270 days under various feeding conditions, and photosynthetic activity was analysed by taking pulse amplitude modulated (PAM) fluorometer measurements. All five species showed stable symbiosis and long-term retention of zooxanthellae. Interspecific differences are discussed. Morphological adaptations for housing zooxanthellae in the digestive glandular system were investigated and documented by histological means.