Ultrastructure of spermatozoa from three genera of crayfish Orconectes, Procambarus and Astacus (Decapoda: Astacoidea): New findings and comparisons

Ultrastructure of spermatozoa of three crayfish genera including Orconectes limosus (Rafinesque, 1817), Procambarus clarkii (Girard, 1852), and Astacus leptodactylus (Eschscholtz, 1823) was studied using transmission electron microscopy. The length of the acrosome was significantly greater in A. leptodactylus (4.5 ± 0.65 μm) than O. limosus (1.7 ± 0.2 μm) and in O. limosus compared to P. clarkii (1.46 ± 0.16 μm). The width of the acrosome was significantly narrower in P. clarkii (2.45 ± 0.2 μm) than O. limosus (4.77 ± 0.51 μm) and in O. limosus compared to A. leptodactylus (8.23 ± 0.9 μm). Also, the length:width ratio was significantly greater in P. clarkii (0.6 ± 0.07) than A. leptodactylus (0.55 ± 0.08) and in A. leptodactylus compared to O. limosus (0.36 ± 0.05). The acrosome complex and nucleus are located at the anterior and posterior of the spermatozoon, respectively. The acrosome complex organelle is divided into two main parts: the main body of the acrosome that is a dense inverted cup-shaped structure and organized into three layers of differing electron densities and extended parallel filaments, and the sub-acrosome zone occupying the central part of the acrosome complex, which is divided into two electron dense areas. The spermatozoon of Orconectes limosus is described for the first time. In addition, an acrosome spike in the spermatozoon of Procambarus clarkii is described. Morphological and biometrical traits of spermatozoa may be used as tools for systematic studies in crayfish, as already reported for many other crustacean taxa.