The Sponge Pump

The sponge pump was analysed and compared with the choanoflagellate pump in order to identify prerequisite properties of the basic pump units which have enabled the development of large sponges. The comparative pump analysis was based on experimentally measured back-pressure pumping-rate characteristics of the demosponge Haliclona urceolus and on mathematical-hydraulic modelling. A curved characteristic was found for H. urceolus, and the maximal pressure rise (at zero flow) which could be delivered by the sponge was about 2·4 mm H2O. First, to unveil the pumping principle and to propose a pump model for sponges a free living choanoflagellate (Monosiga) was considered as representative of a sponge-choanocyte because the two cell types are structurally and functionally identical: a flagellum pumps water through a collar of microvilli acting as a filter. Knowing the flagellum length, beat frequency, wavelength and amplitude the pump head of the choanoflagellate was estimated to be 0·076 mm H2O. Because this pump head is insufficient to handle the pressure drop in a sponge is was instead suggested that the closely spaced flagella in the choanocyte chambers of sponges, possibly confined as a bundle by the apopyle, might all together act as a peristaltic pump being able to create the necessary pump pressure to overcome the resistance in the extensive canal system. It is argued that the basic pump units in a "standard" demosponge are the choanocyte chambers, constituting 30-50% of the wall structure separating inhalant and exhalant canals, and further, that all pump units operate in parallel and at essentially the same flow and pressure rise. Finally, a comparison between choanoflagellates and choanocytes is made in order to draw attention to evolutionary aspects of the sponge pump.