Photoreceptor or statocyst ? The ultrastructure and function of a unique sensory organ embedded in the shell valves of Cryptoplax mystica Iredale & Hull, 1925 (Mollusca:Polyplacophora)

Abstract

Cryptoplax mystica is a common inhabitant of the New South Wales mid-north coast. An elongate chiton with reduced shell valves, it is usually found in narrow crevices and holes in sand-sponge aggregates in the lower intertidal zone. A recent examination of some head, intermediate and tail valves revealed a unique ’sense organ’ imbedded in pigmented tissue immediately below the shells dorsal surface. The structure was found to possess features consistent with a photoreceptive and/or balance function, and to display a degree of complexity hitherto undescribed for the Polyplacophora.