Cirral Activity in the Whale Barnacle Cryptolepas Rhachianechi

Abstract

The cirral activity of the whale barnacle Cryptolepas rhachianechi was studied in a flow tank at different flow regimes. In still water, unidirectional flow, and oscillating flow, the cirral fans of adult animals always beat in the direction of the rostrum. Adults did not respond to water current from the carinal direction by facing the cirral fan into the current; however, during copulation they could turn the cirral fan so it faces the carina. Newly settled animals responded to flow from the carinal direction and to oscillating flow by facing their cirral fans towards the oncoming current, but there is no synchronization between changes in water flow direction and the change in cirral direction. Since these barnacles are normally exposed only to unidirectional currents, with no need to respond to flow from the carinal direction or to oscillating flow, it seems likely that they have lost the ability to change the direction of their cirral beats. This loss of the ability to respond to changes in current direction is a specialization of C. rhachianechi related to its epizoic mode of life.