Distribution and feeding in the onuphid polychaete,Diopatra cuprea (Bosc)

Population density of the onuphid polychaete Diopatra cuprea is poorly correlated with particle size distribution of the substratum. It varies directly, however, with current velocity. Measurements of the volume of oxygen drawn through the tube by the inhabitants' rhythmic activities, and the volume consumed under similar conditions, indicate that the rate of oxygen utilization is unusually low; therefore, the influence of current velocity cannot be exerted through its effect on oxygen supply. We suggest that the worm's tube, which protrudes several centimeters above the substratum in the form of an inverted hook, is a food-catching device whose efficiency is governed by the volume of water flowing past. This hypothesis is supported by the identity of many species found both in the gut and on the tube. We also suggest that the tube-irrigating activities permit the animal to test the medium for the presence of chemical stimuli emanating from food caught by the tube; supra-threshold concentrations of these stimuli elicit the feeding response.