Fine structural aspects of anthozoan desmocyte development (Phylum Cnidaria)

Abstract

The fine structural changes associated with the differentiation of skeletogenic cells into cells specialized in binding soft tissues onto skeletal structures are described in the gorgonian coral, Leptogorgia virgulata (Lam.). These binding cells are called desmocytes. The sequence of events in desmocyte development includes: growth of the plasma membrane, invagination of the mesoglea-end of the cell, expansion of the axis-end of the cell, loss of organelles involved in skeletogenesis, proliferation of double vesicles and transformation of double vesicles into cytoskeletal rods. Double vesicles appear either cup-shaped or as a vesicle within a vesicle in sectioned material. These observations of desmocyte development are compared to previous light microscopical observations on desmocyte development in diverse forms of anthozoans. Similarities in desmocyte development throughout the class include invagination of the differentiating cell, formation of a pectinate mesogleal margin and formation of an array of cytoskeletal rods at the axis-end of the cell. Comparison with available information on the development and fine structure of desmocytes in the cnidarian classes Scyphozoa and Hydrozoa shows these similarities do not extend across class boundaries and, therefore, common ancestry between the three classes of cnidarian desmocytes seems remote if, indeed, such an ancestral cell existed at all.