Spermatogenesis of the spider crab Maja brachydactyla (Decapoda: Brachyura)

This study describes spermatogenesis in a majid crab (Maja brachydactyla) using electron microscopy and reports the origin of the different organelles present in the spermatozoa. Spermatogenesis in M. brachydactyla follows the general pattern observed in other brachyuran species but with several peculiarities. Annulate lamellae have been reported in brachyuran spermatogenesis during the diplotene stage of first spermatocytes, the early and mid-spermatids. Unlike previous observations, a Golgi complex has been found in mid-spermatids and is involved in the development of the acrosome. The Golgi complex produces two types of vesicles: light vesicles and electron-dense vesicles. The light vesicles merge into the cytoplasm, giving rise to the proacrosomal vesicle. The electron-dense vesicles are implicated in the formation of an electron-dense granule, which later merges with the proacrosomal vesicle. In the late spermatid, the endoplasmic reticulum and the Golgi complex degenerate and form the structures-organelles complex found in the spermatozoa. At the end of spermatogenesis, the materials in the proacrosomal vesicle aggregate in a two-step process, forming the characteristic concentric three-layered structure of the spermatozoon acrosome. The newly formed spermatozoa from testis show the typical brachyuran morphology.