The Sensitivity and Control of the Scallop Mantle Edge

Abstract

ABSTRACT Application of mechanical stimulation or crude starfish extracts to the mantle edge of Aequipecten irradians elicited afferent impulse activity in the radial pallial nerves and local movements of the stimulated mantle edge. The evoked afferent spike activity was not recorded from primary receptor cells. The local mantle edge movements were controlled by peripherally located neurones and resembled jet formation on the velum of intact scallops. The central efferent neurones that supply the adductor muscle and much of the mantle edge are situated in the visceroparietal ganglion. Cobaltous chloride back-filling of the radial pallial nerves of the right side revealed the routes of the nerve fibres and the locations of the cell bodies in the visceroparietal ganglion. One group of motor neurones has fibres that are spatio-topically arranged across the visceroparietal ganglion and play a role in jet formation on corresponding portions of the mantle edge on both valves. It is apparent that axons from this group of mantle edge efferents traverse the ganglion without chemical synaptic connection. Two groups of mantle edge efferents that control concerted movements of the mantle edge on both shells appear to have cell bodies in the lateral margins of the dorso-central lobes. One group of motor neurones controls the raising of the velum curtain to an erect position around the shell margin. The output from the second group of efferents can be synchronized with the motor output to the adductor muscle to ensure that the velum folds into the mantle cavity, and thus is protected, as the shells are closed. Fibres in the radial pallial nerves have conduction velocities of up to 2·35 m/s at a temperature of 25 °C.