Embryology and gonad development in Oscheius shamimi sp. n. (Nematoda: Rhabditida)

A new species of Rhabditinae collected from compost, is described and illustrated together with observations on embryonic and post-embryonic development. Oscheius shamimi sp. n. is characterised by a medium−sized body (female: L = 0.76-1.52 mm, a = 12-20, b = 4.2-6.3, c = 6.8-13.8, c' = 4.1-5.8, V = 45-51), finely annulated cuticle; slightly demarcated lip region; lips fused to form three doublets; six lines in lateral field; small stoma with isomorphic metastegostom; cylindrical pharyngeal corpus; slightly protruded vulval lips with subventral cuticular flap; long, proximally dilated, rectum; 53-61 µm long, robust spicules with long capitula having strongly cuticularised ventral walls; pseudopeloderan bursa with nine pairs of genital papillae in 1 + 1 + 1/3 + 3 + ph configuration and six to seven pairs of copulatory muscle bands. Oscheius shamimi sp. n. is amphimictic with a 1:1 sex ratio. The eggs are ovoid and smooth-shelled and measure 48-78 × 37-48 µm. Most eggs are laid in the late stages of embryonation. The embryonation time was 14-15 h at 25 ± 2°C. The genital primordium was orientated obliquely to the longitudinal axis and did not show division of primordial nuclei during the first moult. The didelphic female reproductive system was formed as a result of anterior and posterior elongation of the primordium while the monorchic reproductive system of the male developed from an anterior elongation of the primordium. The life cycle from egg to adult was completed in 3-3·5 days at 25 ± 2°