Modification of the spermatic structure of the crab Cancer setosus (Molina, 1782) (Decapoda: Brachyura) during induced acrosomal reaction

The spermatozoon of Cancer setosus consists of a spherical acrosome and a cup-shaped nucleus surrounding the lowest zone of the acrosome and widening at the equatorial area of the acrosome. The spermatozoa extracted from the seminal receptacle of the female and placed in sea water for 15 min underwent the acrosome reaction, which started with the elongation of the acrosomal vesicle followed by the extrusion of its contents. Subsequently, the perforatorium projected forward ≈ 1µm beyond the apical end of the extruded acrosomal vesicle contents, forming an acrosomal filament with a trident-shaped structure on the apical end.