ISSN : 1225-3480
The ultrastructural characteristics of germ cell development during spermatogenesis and mature sperm morphology of in male Scapharca subcrenata were investigated by transmission electron microscope observation. Spermatogonia are located nearest the outer wall of the acinus, while spermatocytes are spermatids are positioned nearer the accessoy cells. The accessory cells, which is in close contact with developing germ cells, contained a large quantity of glycogen particles and lipid droplets in the cytoplasm. Therefore, it is assumed that they are involved in suplying of the nutrients for germ cell development. The morphologies of the sperm nucleus and the acrosome of this species are the oval shape and cone shape, respectively. Spermatozoa are approximately 45-50 μm in length including a sperm nucleus (about 1.30 μm in length), an acrosome (about 0.59 μm in length), and tail flagellum (about 43-47μm). The axoneme of the sperm tail shows a 9 + 2 structure. As some characteristics of the acrosomal vesicle structures, the right and left basal rings show electron opaque part (region), and the anterior apex part of the acrosomal vesicle shows electron opaque (region). These characteristics of the acrosomal vesicle were found in the family Acinidae and other several families in the subclass Pteriomorphia. These common characteristics of the acrosomal vesicle in the subclass Pteriomorphia can be used for phylogenetic and taxonomic analysis as a taxonomic key or a significant tool. The number of mitochondria in the midpiece of the sperm of this species are five, as one of common characteristics appear in most species in the family Arcidae and other families in the subclass Pteriomorphia. The acrosomal vesicle of Arcidae species does not contain an axial rod and several transverse bands in acrosome, unlkely as seen in Ostreidae species in the subclass Pteriomorphia, These characteristics can be used for the taxonomic analysis of the family or superfamily levels as a systematic key or tools.
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