Defense reaction in the pond snail Planorbis corneus. I. Activity of the shell-moving and respiratory systems

Abstract

1. In the intact pond snail Planorbis corneus, tactile or electrical stimulation of the skin evoked a biphasic general defense reaction. A weak stimulation evoked only the first phase of the reaction, represented as a fast pulling of the shell towards the head. With stronger stimulation, this phase was followed by the second phase that was comprised of three components: detachment from the substrate, slow retraction of the body into the shell, and letting out of air from the lung through the pneumostome. 2. About 70 motor neurons (MNs) of the columellar muscle have been revealed in different ganglia by means of their cobalt back-filling through the cut columellar nerve. A complicated pattern of electrical coupling was found for different groups of MNs. Excitation of individual MNs, evoked by current injection, resulted in contraction of the columellar muscle (CNS-columellar muscle preparation). The strongest contraction was evoked by the cerebral MNs; fast small contraction by the parietal MNs; and slow, long-latency contraction, by the pedal MNs. 3. In the same preparation, electrical stimulation of the cutaneous (lip) nerve evoked biphasic contraction of the columellar muscle (a first phase lasting approximately 3 s, and a second phase of up to 1 min). The temporal pattern of this response was similar to that of the defense reaction in the intact animal. A weak stimulation evoked only the first phases of the reaction, while a stronger stimulation evoked both phases. The amplitude of both the first and the second phase was graded with the strength of stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Neuroanatomical, immunocytochemical, and physiological studies of the pharyngeal retractor muscle and its putative regulatory neurons playing a role in withdrawal and feeding in the snail, Helix pomatia

“…A similar distribution of labeled neurons can be observed after the application of cobalt backfilling through the columellar nerves in both Lymnaea and Planorbis (Ferguson and Benjamin 1991a;Arshavsky et al 1994a), indicating that the CM is innervated from different loci in the CNS. If we compare the number and location of neurons that innervate the PRM with those that innervate the CM in Helix (Samygin and Karpenko 1980), we can establish that the PRM neurons are located in the same loci, but that the PRM is represented by markedly fewer numbers of neurons.…”

Fluid and osmolyte recovery in the common pond snailLymnaea stagnalisfollowing full-body withdrawal

“…shell-invading leeches and flatworms (Townsend and McCarthy, 1980;Brönmark and Malmqvist, 1986) versus shell-crushing sunfish or crayfish (Alexander and Covich, 1991;Brown, 1991). Additionally, and central to the present study, snails can perform graded withdrawal of soft tissue into their shells corresponding to the intensity of the predatory attack (Arshavsky et al, 1994). Pulmonate snails, such as the common pond snail Lymnaea stagnalis (L.), exhibit emergence behavior to escape predation but when the predatory threat is imminent, L. stagnalis can also complete full-body withdrawal by ejecting up to 60% of its total hemolymph volume (Schlichter, 1981), which averages 0.45·ml·g -1 snail body mass (van Aardt, 1968).…”