Spermatozoon ultrastructure in the sphaerularioidid nematode Contortylenchus genitalicola (Tylenchomorpha: Sphaerularioidea)

The spermatozoa of the insect-parasitic tylenchomorph nematode Contortylenchus genitalicola (Tylenchomorpha: Sphaerularioidea) were studied with the transmission electron microscope. The immature spermatozoa from the testis are unpolarised cells with a centrally located nucleus lacking a nuclear envelope. The cytoplasm contains mitochondria and specific components, membranous organelles (MO) and fibrous bodies (FB). The MO are spherical vesicles with an internal system of finger-like invaginations of the membrane; the cylinder-like FB consist of tightly packed parallel fibres. The mature (activated) spermatozoa from the uterus are bipolar cells with the anterior pseudopod and posterior main cell body (MCB), which includes the nucleus, mitochondria and MO. The MO are attached to the spermatozoon plasmalemma and open to the exterior via pores. FB were not observed but their content may be transformed into the pseudopod cytoskeleton. In general, the spermatozoa of C. genitalicola well resemble those of free-living and parasitic nematodes from a variety of the taxa belonging to the order Rhabditida sensu De Ley & Blaxter (2002). The presence of the MO in C. genitalicola spermatozoa may be considered as an important cytological character that differentiates the superfamilies Sphaerularioidea and Tylenchoidea within the infraorder Tylenchomorpha. The plant-parasitic Tylenchoidea are characterised by a total absence of MO at all stages of sperm development.