Fine structure of spermiogenesis with special reference to the spermatid morulae of the freshwater mussel Prisodon alatus (Bivalvia, Unionoidea)
✍ Scribed by Edilson Matos; Laura Corral; Carlos Azevedo
- Publisher
- John Wiley and Sons
- Year
- 1998
- Tongue
- English
- Weight
- 592 KB
- Volume
- 238
- Category
- Article
- ISSN
- 0362-2525
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✦ Synopsis
Within the testicular cysts of the mussel Prisodon alatus are numerous somatic host cells described as Sertoli cells (SC), each containing a variable number of young spermatid morulae. Among them, several free spermatid morulae, spermatids, and spermatozoa were observed. Each free spermatid morula is surrounded by an external membrane. The early spermatids enclosed within the morulae have dense and homogeneous chromatin, and the cytoplasm occupies little space around the nucleus. Later, during spermiogenesis, the SC show lysis and disrupt to liberate the spermatid morulae. The membrane of the free morula is then disrupted, releasing the young spermatids. The SC disappear just after the appearance in the testis of a large number of free young spermatids. The nucleus of each free spermatid becomes gradually smaller and denser by the appearance of a granular pattern of condensed chromatin. During the maturation phase of the spermatids, the cytoplasm becomes more voluminous, and mitochondria and centrioles are more evident. Then, flagellogenesis occurs, and the nucleus gradually condenses into thicker strands. In the mature sperm, the apical zone has a disc-shaped acrosomal vesicle and the midpiece contains five mitochondria and two centrioles located at the same level. The flagellum has the common 9ϩ2 microtubular pattern. The results are discussed with particular reference to Sertoli cells and clusters of spermatid morulae with those of species of closely related taxa in the bivalves.