Pressures generated by the pumping mechanism of some ciliary filter-feeders

An apparatus is described that enables measurements to be made of the low pressures generated by ciliary filter-feeders. Such pressures range from 0.1 to 5.2 mm of water (10 to 520 dyn cm^?2) with the higher pressures in bivalves with long siphons. In these bivalves the frictional resistance of the siphons accounts for a major part of the total resistance to water flow. Pressures observed in bivalves with short siphons, in tunicates, and in sponges are all similar. Hydrodynamical equations have been used to see whether the pressures can be predicted from the dimensions and pumping rate of the bivalve Mya arenaria L.