Ultrastructure of spermatozoa in the free-living marine nematode Monoposthia costata (Chromadoria, Desmodorida)

摘要

The spermatozoa from both male and female of the free-living marine nematode, Monoposthia costata (Desmodorida, Monoposthiidae), were studied using electron microscopy. The spermatozoa are cells, the surface of which is covered with numerous filopodia. Nuclei of the sperm cells are taper-shaped and composed of condensed chromatin without a nuclear envelope. There is a centrally located electron transparent halo filled with mitochondria. The peripheral cytoplasm is devoid of organelles and filled withfilaments, which also strengthens the filopodia. The spermatozoa of M. costata exhibit the main ultrastructural features characteristic of nematodes: the absence of an acrosome, an axoneme and a nuclear envelope. However, in spermatozoa of M. costata and other desmodorid studied the membranous organelles were not found. In this respect sperm cells of M. costata differ from those in monhysterids and secements, but resemble those of Chromadorida. It could be evidence of the phylogenetic closeness of these two orders of nematodes.