Cirral Activity and Feeding in the Coronuloid Barnacles Tesseropora Rosea (Krauss) and Tetraclitella Purpurascens (Wood) (Tetraclitidae)

Adult T. rosea and T. purpurascens are extension-feeding planktivores, dependent on water currents to evoke extension of the cirral fan. T. rosea displays testing activity in still and slowly moving water and respiratory pumping beat in a moderate water current, but requires a fast current for cirral extension and feeding. T. purpurascens displays pumping beat in still and slowly moving water, and performs cirral extension in a moderate water current. Fast flow causes distortion of the cirral fan in T. purpurascens and often provokes cirral withdrawal.

Juveniles of T. purpurascens show the same cirral responses as adults. Juveniles of T. rosea display pumping beat and normal beat in still, slowly moving and moderate water flow, but withdraw the cirri in response to fast flow. Transitional behavior is shown by T. rosea individuals of about 2 mm aperture length.

The cirral responses to water flow in the two species are related to habitat. T. rosea inhabits wave washed rocks subject to fast water flow. T. purpurascens occupies more sheltered habitats in which water flow is reduced. Juvenile T. rosea appear to feed when immersed and to survive fast flow by a protective withdrawal of the delicate cirri.

The observation of cirral beating in a juvenile coronuloid adds to the number of cases of convergent evolution of cirral beating among thoracican barnacles. It also raises the possibility that adult balanoids with cirral beating are a product of neotenic evolution.