Abstract

In order to analyse the roles of Keber's valve for foot manipulation in the clam Nodularia douglasiae, the anatomy and hemolymph flow in the cardiovascular system were detected by magnetic resonance imaging. The superficial layer of the foot was covered by a dense muscle layer, which extended to the dorsal side and connected with the shell. This closed space, the foot chamber, had an inlet (anterior aorta) and an outlet (Keber's valve). At rest, in the beginning of the systolic phase, flows in the anterior aorta and the pedal artery increased, followed by the pedal and visceral sinuses. Then, these flows ceased at the end of the systolic phase, followed by inflow to the ventricle in the diastolic phase. Therefore, the compliance of the foot chamber is low enough to transfer pressure pulses to the visceral sinus. Extension of the foot started with relaxation of the foot muscle, so the compliance of the foot chamber increased. Then, Keber's valve closed, so that the hemolymph filled the foot haemocoel. Retraction of foot is initiated by the opening of Keber's valve. Judging from these results, Keber's valve and the foot chamber are essential for circulation at rest, foot extension and retraction.