Ultrastructural study of spermatophores and spermatozoa in Uca uruguayensis (Decapoda, Brachyura, Ocypodidae)

Abstract

The present study shows that this species has a very simple spermatophore structure, consisting of a sperm mass embedded in seminal fluid and surrounded by a two layered acellular wall. Beneath the wall, there is a translucent zone lined by dense granules. These granules could be part of the spermatophore wall. The seminal fluid is composed by a viscous granular matrix and electron-dense granules with homogeneous aspect. The spermatophores were observed densely packed in the middle vas deferens (MVD) and laxly packed in the posterior vas deferens (PVD), suggesting an increment of the amount of seminal fluid. This increment would provide protection and maintenance to the spermatozoa. Mature spermatozoa have the typical structure of brachyuran crabs with a complex acrosome, cupped by the nucleus, and a thin cytoplasmic band between the former elements. Spermatozoa have spike-like arms with microtubules and chromatin, suggesting that they are extensions of the nucleus. The length to width rate of the acrosome is in the range observed for the rest of Thoracotremata. The acrosome of this species presents the bilayered appearance characteristic among brachyurans. The perforatorium has fibrous aspect attributed to the presence of tubular membranous structures. In summary, the spermatozoal features display the typical brachyuran characters, although the characteristic “onion ring” lamellation present in the thoracotremes acrosome was not observed.
Keywords: Brachyura, Ocypodidae, spermatophore, spermatozoa.