Ultrastructure of spermatozoa and spermiogenesis in the hydrozoanCordylophora caspiawith comments on structure and evolution of the sperm in the Cnidaria and the Porifera

Publisher Website
Google Scholar
Abstract
Spermiogenesis in the hydroid, Cordylophora caspia, illustrates many of the features of this process in cnidarians and those of primitive sperm structure in primitive metazoans. The electron-dense vesicles or granular material in the acrosomal region of the cnidarian sperm may have evolved into the typical cup-shaped acrosomal vesicle found in sperm fiom many phyla. Cnidarian sperm are of the primitive type, plesiosperm, with a well-differentiated centriolar complex; a similar structure is also found in many other phyla which may have retained the primitive sperm. The distal centriole in the Cordylophora sperm and in other cnidarian sperm connects to a pericentriolar complex. A comparison of spermiogenesis and sperm structure between the Cnidaria and the Porifera, briefly discussed in this paper, supports the suggestion of Afzelius (1972) that the sperm in the Porifera has arisen independently of the primitive sperm in the Cnidaria. Porifera sperm seem to lack the typical midpiece containing two centrioles surrounded by a few mitochondria and an anchoring fiber apparatus. Porifera sperm appear to arise primarily fiom choanocytes. The morphology of the sperm in the Porifera shows considerable morphological diversity.