Feeding habits of Calma glaucoides (Alder & Hancock, 1854): its adaptive structures and behaviour.

Abstract

Calma glaucoides (Alder & Hancock, 1854) is an aeolid nudibranch inhabiting European (Atlantic and Mediterranean) Western and Southern coasts. Adults feed on fish eggs, thus being found near spawning sites on the underside of boulders or in small crevices, where male fish nest. This aeolid has an atypical uniseriate radula. Little is known about formation or function of this radula, but it is believed that such a peculiar morphology is related to adult's feeding habits. The feeding behaviour of individuals could be observed in aquaria. It was also possible to study not only radulae from individuals of different sizes but also the damage caused by radula action upon fish egg membranes. These were visible under SEM after critical point drying of empty eggs. SEM images suggest that the radula is used as a saw. After the egg is "opened" the yolk and embryo are sucked out with the help of strong buccal musculature, leaving the external membrane of the egg almost intact. The way these animals puncture fish eggs, associated with the early development of their radula, lead us to conclude, that there seems to be no food size constraint, as previously had been thought.