Capture of small cells by the copepod Eucalanus elongatus

Calanoid copepods feed by detecting and actively responding to relatively large individual cells and by accumulating smaller cells in a relatively passive manner by low amplitude flapping of the second maxillae. Films of Eucalanus elongatus passively collecting 13-µm Thalassiosira weissflogii cells show that cells flow between the setae from the outer to the inner surface of the second maxillae. They are then funneled medially toward the setal tips and mouth, usually without adhering to the setae. The observed patterns of water flow contradict both the early descriptions of filter feeding and the expectation of negligible flow through setae in a low Reynolds number environment.