Water pumping in the penduculate barnacle Conchoderma auritum

The cirral activity of the penduculate barnacle, Conchoderma auritum, was studied in a flow tank. The barnacles were exposed to different experimental water velocities and the response of the barnacles was recorded using a video system. In still and slow-moving water the barnacles show rhythmic cirral activity, the cirri extend and then withdraw into the mantle cavity. When water flow is accelerated the barnacles switch from rhythmic cirral activity to prolonged cirral extension, in which the cirri are extended in the water flow, facing the current. The water velocity at which barnacles switch from rhythmic activity to cirral extension depends on the size of the animal. During the rhythmic activity of Conchoderma water is pumped into the mantle through the ears. The prosoma serves as a piston which inhales the water into the capitulum and then ejects it at the apical end of the capitulum opening. This finding contradicts the generally accepted notion that the function of the ears of C. auritum is water ejection.