Distribution and Ultrastructure of Ciliated Sensory Receptors in the Posterior Mantle Epithelium of Dentalium rectius (Mollusca, Scaphopoda)

Abstract

AbstractThe scaphopod mantle cavity opens posteriorly via the pavilion, a siphon‐like extension of the posterior mantle through which the respiratory currents pass. The pavilion was examined for ciliated sensory cells in Dentalium rectius Carpenter, 1865, using scanning and transmission electron micropscopy. Three types of sensory receptor were distinguished on the basis of number, length and ultrastructure of the associated cilia. Receptors with 2–5 cilia of ˜ 1.7 μm length lined the pavilion edge. A second type, possessing 1–2 cilia, ˜ 8.2 μm in length, was found throughout the internal and on part of the external surface of the pavilion. The third receptor type consisted of a rigid bundle of 16–40 cilia with a length of ˜ 14.4 μm, and was present close to the periphery and at the base of the pavilion near the entrance to the mantle cavity. The structure and distribution of these cells are similar to peripheral chemo‐ and mechanoreceptors which sample respiratory currents and the surrounding environment in other molluscs, but they may assume a greater functional significance in scaphopods due to the absence of an osphradium in this class.