Cropping of sea anemone tentacles by a symbiotic barnacle

As sessile animals, barnacles (Cirripedia: Thoracica) are generally suspens ion feeders, extending their cirri into the surrounding water To collect fo od particles (1). Although it has been suggested that some symbiotic barnac les obtain nutrients directly from their hosts, either by absorbing body fl uids (2-4) or by rasping the host's tissue (4-6), most of these cases are i nferred from their morphology. Direct evidence, such as gut content analysi s, has been limited (for an exception, see ref: 5), and no actual feeding o n their hosts has been observed. Koleolepas avis (Hiro, 1931) is a peduncul ate barnacle symbiotic with the sea anemone Calliactis japonica, which live s on gastropod shells occupied by large hermit crabs (7), mainly Dardanus a rrosor. Symbiotic relationships between various hermit crabs and sea anemon es have been well documented (8), but the relationship between the barnacle and its host sea anemone has been virtually unknown. From February to Apri l 1996 we collected living individuals of K. avis from lobster nets landed at Minabe Fishery Port, southwestern Japan (33 degrees 44' N, 135 degrees 2 0' E). On the basis of behavioral observations in the laboratory and analys es of fecal pellets and gut contents, we concluded that this barnacle feeds actively on its host's tentacles.