Plasticity of feeding behavior in the opisthobranch mollusc Navanax.

Several forms of plasticity of feeding behavior were investigated in Navanax. Navanax is a gastropod mollusc which lacks a radula, and ingests prey with suction caused by rapid pharyngeal expansion. Feeding is little affected by handling or posture and is resistant to the noxious stimulus of cutting through the body wall. Feeding is affected by arousal, as shown by a decrease in latency following initial exposure to food. The feeding response also habituates, as shown by an increase in latency when feeding responses are elicited without allowing animals to engulf food. The latency increase is not likely to be due to motor fatigue, since it can be partially reversed by dishabituation with an alternate prey species. Continued feeding causes satiation, as shown by increased feeding latencies and eventual cessation of feeding after a mean weight gain of 42.0% of initial animal weight (N = 12). Another form of plasticity occurs when Navanax are presented with food too large to swallow whole. Navanax either cease to respond after a few presentations, perhaps due to habituation, or maintain suction on the partially swallowed prey for an extended period of time. During extended sucks, the more deeply ingested portions are digested.