THE FEEDING BIOLOGY OFPODARKE PUGETTENSIS(POLYCHAETA: HESIONIDAE)

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Abstract
Several aspects of the feeding biology of free-living P. pugettensis from San Juan Island, Washington, USA, were examined: potential and actual diet, rate and degree of digestion and nature of the fecal material; structure and function of the pharynx; and detection and evaluation of potential prey. This polychaete is carnivorous, ingesting a wide variety of small benthic invertebrates. Harpacticoid copepods constituted the bulk of the diet in the field population examined. Ingested animals may be thoroughly digested by the time they reach the hindgut but plant material may be undigested. The gut passage time averages 18 h, which is slow for a small carnivore with a straight gut. This may be necessary because Podarke is limited in the food it consumes by relative prey availability, reflected in guts less than half full on the average, and maximizes its rate of nutrient absorption by slowly and thoroughly digesting each prey item. The unarmed pharynx acts as a 2-stage pump, with 2 thick-walled muscular regions and 2 thinner-walled valves. The massive walls of the muscular regions consist mostly of radial muscle fibers which can rapidly open the pharynx, sucking in prey. The eversible pharynx is well adapted to a diet of small moving animals. P. pugettensis may utilize vibration sensing, direct touching and chemoreception to detect and evaluate potential prey. Size of the prey appears to be the most critical factor influencing prey selection. This predator could probably consume a significant portion of the production of co-occurring benthic copepod populations.

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