Studies on the Epidermis of Temnocephala Vi. Epidermal Topography of T. Novaezealandiae and Other Australasian Temnocephalids, With Notes on Microvillar and Coated Vesicle Function and the Evolution of a Cuticle.

Abstract

The surface of T. novaezealandiae is subdivided by a system of grooves marking interepithelial boundaries of the epidermis. Elongated cilia occur in association with clusters of uniciliate receptors on the tentacles and body. The conspicuous mass of very long cilia characteristic of the ventral surface of T. dendyi and T. minor is lacking in T. novaezealandiae. A pair of ridges marks the lateral borders of T. novaezealandiae, and a peripheral ridge outlines the attachment disc. The dorsal epidermis shows an intricate surface geometry. Fine thread-like structures overlie the epidermal surface, a feature which may parallel early stages of cuticle development. During the evolution of a cuticle among annelids, an epidermal microvillar fringe is often lost, but epicuticular fragments representing microvillar distal segments are retained and function to stabilize a mucoid coat. The microvilli of coated epithelia probably have a similar function, and the microvillar tips represent a layer of hemidesmosomes raised above the epithelial surface. Coated vesicles are evidently involved in the formation of desmosomal structures, including microvillar tips. [AS]