The defensive behaviour of 11 species of sea anemone when attacked by the nudibranch Aeolidia papillosa is described. An attempt is made to correlate their defensive responses with the habitat, and with the food preferences of Aeolidia. Actinia equina responds first by tentacle and column retraction, and then by inflation of the column, pedal locomotion, and detachment from the substrate. Anthopleura elegantissima responds in similar ways, but Anemonia sulcata, which has much longer tentacles, uses these in active defence against the eolid. Anemonia also crawls away but it does not detach.
Actinia, Anthopleura and Anemonia are the preferred foods of Aeolidia. They commonly live in dense colonies where locomotion and detachment are likely to result in escape. Tealia felina is less preferred and is much less responsive when attacked by Aeolidia.
Anemones which possess acontia normally eject these when they are attacked by Aeolidia. Although Aeolidia does occasionally eat acontian anemones, evidence is presented which suggests that acontia have some deterrent effect on this predator. Although most acontian anemones are probably able to move by pedal locomotion and to detach from the substrate, these responses are much less frequently given than by Actinia equina.