Multi-oscula sponges are organisms composed of aquiferous modules, each of which draws water through its canal system by means of pumping units (choanocytes, Cs, in choanocyte chambers, CCs) such that the filtered water leaves the module as an exhalant jet through the osculum of the module. Here we compare relations between the characteristic parameters of sponge volume (V), osculum cross-sectional area (OSA), exhalant jet speed (U 0), and filtration rate (F) of single-osculum explants and individual aquiferous modules of multi-oscula explants of the demosponge Halichondria panicea. The latter modules are identified by observing from which osculum the surface administered dye will emerge. There is fair agreement in results between the two types of modules. For both types, the filtration rate is a linear function of the modules’ volume, with average values of volume-specific filtration rate (F V) of 1.8 and 1.2 ml min −1 cm −3 for single- and multi-oscula sponge explants, respectively. This and data from the literature for 5 demosponges support the hypothesis that the density of pumping units are of the same order of magnitude for the present given species and for some other demosponges.