Oral mechanoreceptors inTritonia diomedea

Summary

• 1. Behavioral analysis of normal feeding inTritonia diomedea revealed a complex series of movements designed to deal with a structurally challenging prey organism, the sea whipVirgularia (Fig. 1). The prey is often swallowed in its entirety during a single bout of feeding which includes movements to bite and swallow the sea whip, and to break its calcareous style (Fig. 2).

• 2. Separate and combined presentation of mechanical and chemical cues similar to those associated with normal feeding demonstrated that each type of sensory stimulus influences the nature of the ingestion movements performed. Mechanical stimuli, in the presence of appropriate chemical cues, inhibit biting and elicit swallowing. Repeated biting is elicited by chemical cues alone. With chemical cues absent, mechanical stimuli within the buccal mass elicit an ambiguous combination of ingestion and ejection movements. A flow diagram of the decision-making process (Fig. 6) is proposed.

• 3. Intracellular stimulation of single central mechanoreceptor neurons described in the previous paper (Audesirk, 1979) often results in movements of the buccal mass, sometimes resembling swallowing and sometimes ejection. Cycles of activity in presumed motor neurons of the buccal ganglia can be elicited either by brief intracellular stimulation of mechanosensory neurons or by pressure on areas of the oral tube known to be densely innervated by these receptors.