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 ex perimental water velocities and the response of the barnacles was reco rded using a video system. In still and slow-moving water the barnacle s show rhythmic cirral activity, the cirri extend and then withdraw in to the mantle cavity. When water flow is accelerated the barnacles swi tch from rhythmic cirral activity to prolonged cirral extension, in wh ich the cirri are extended in the water flow, facing the current. The water velocity at which barnacles switch from rhythmic activity to cir ral extension depends on the size of the animal. During the rhythmic a ctivity of Conchoderma water is pumped into the mantle through the ear s. The prosoma serves as a piston which inhales the water into the cap itulum and then ejects it at the apical end of the capitulum opening. This finding contradicts the generally accepted notion that the functi on of the ears of C. auritum is water ejection.