PROTECTION OF THE NUDIBRANCH AEOLIDIA-PAPILLOSA FROM NEMATOCYST DISCHARGE OF THE SEA-ANEMONE ANTHOPLEURA-ELEGANTISSIMA

The nudibranch Aeolidia papillosa is resistant to being harmed by the nematocysts of its prey, the sea anemone Anthopleura elegantissima. Th is study tested whether the epidermal mucous coat of A. papillosa elic its lower levels of nematocyst discharge by A. elegantissima than othe r non-anemone-eating gastropods, the nudibranchs (Phidiana crassicorni s and Cadlina luteomarginata) and a shelled gastropod (Lithopoma gibbe rosum). Mucous samples were collected from each species of gastropod o n glass coverslips, and they were put in contact with the tentacles of anemones. The density of nematocysts discharged in response to each s ample was enumerated. Relatively low densities of nematocysts were dis charged by A, elegantissima in response to mucus of A. papillosa and a negative control (no mucus); high nematocyst densities were found in mucous samples from non-anemone-eating gastropods. This suggests that the mucous coating of A. papillosa has specific properties that provid e protection for the nudibranch from being stung during predatory enco unters with A, elegantissima. The response of A. elegantissima to cont act with whole gastropods was also tested. Individuals of A. papillosa appeared to be stung by anemones upon initial contact, which caused t he nudibranchs to retreat. However, there was no visible harm to the n udibranchs, and they returned to attack and eat the anemones. The two other nudibranch species were stung and consumed by the anemones, and the L. gibberosum retreated into its shell for protection. Thus, A. pa pillosa was the only gastropod species that remained unharmed during e ncounters with A. elegantissima and whose mucus did not elicit strong nematocyst discharge.