New pattern of nematode spermatogenesis revealed by ultrastructural observation of Anaplectus granulosus (Plectidae, Plectida)

This paper presents the first comprehensive detailed transmission electron microscope observations of sperm development and structure of a plectid nematode. Sperm development of Anaplectus granulosus resembles that of nematodes of the order Rhabditida, known as the rhabditid pattern of spermatogenesis. It includes formation of complexes of fibrous bodies (FB) with membranous organelles (MO), which appear in spermatocytes; the complexes dissociate in the spermatids. The mature spermatozoa are bipolar cells subdivided into a pseudopod and a main cell body containing a nucleus with nine singlet centrioles, peripheral mitochondria and MOs. However, the development and structure of sperm in A. granulosus deviates remarkably from the common rhabditid pattern by an unusual early transformation of FBs into large amorphous masses in the spermatids; the subsequent formation of a concentric structure of immature spermatozoa with a predominant amorphous mass around the central nucleus and thin peripheral cytoplasm with organelles (MOs and mitochondria); and by the transformation of MO in mature spermatozoa into simple cisterns. Thus, the pattern of spermatogenesis of A. granulosus supports the close relations of Plectida and Rhabditida, but specific peculiarities of the sperm development delineate Plectida from Rhabditida and other orders.