Ultrastructure of mature spermatozoa in the lumen of the spermatheca and middle vas deferens of Paratelphusa hydrodromous (Crustacea)

Mature spermatozoa of P. hydrodromous are spherical or ellipsoidal, composed of an acrosome surrounded by a cup shaped nucleus. The acrosome is divided into a distal apical cap and an acrosomal vesicle, which is enclosed in the cup shaped nucleus. The apical cap is raised in its middle to form the apical cone. Below the apical cap is the subcap region. The acrosomal vesicle has a central canal, which encloses dense tubules. A thin inner layer, middle acrosomal rays layer and an outer acrosomal vesicle layer surrounds the central canal. Radial arms are absent. Along the posterior region of the spermatozoa are posterior median processes. Within the lumen of the mid vas deferens, spermatozoa are seen encased in oval or spherical spermatophores. Spermatophores are without distinct lining membranes. In the spermatophore lumen spermatozoa exist free or two to three of them tightly packed to form a unit. Each unit is surrounded by an electron-lucent halo, embedded in a moderately dense spermatophore ground substance. The spermatozoa are seen embedded in a flocculent material possibly the seminal plasma. There was hardly any structural difference between spermatozoa present in the lumen of the spermatheca and those present in the mid vas deferens (MVD). KEY WORDS: Spermatheca, middle vas deferens, ultrastructure, crabs, spermatozoa. Tropical Freshwater Biology, 10 (2001) 35 - 4