Study of Plectidae (Nematoda) from Ukraine. Variability of male sexual characters in Plectus pusteri Fuchs, 1930

A population of Plectus pusteri from Ukraine, based on 20 females, 2 intersexes, 4 males with one; 20 males with two and 20 males with three precloacal midventral tubular supplements, is described and compared with related species. Variability of the spicule length, and length and position of tubular supplements are reported. The use of male sexual characters in the taxonomy of the genus Plectus and in the identification of its species is discussed. Neither number, position nor length of precloacal midventral tubular supplements can serve as differential characters for species due to their high variability. Since no males completely lacking tubuli were found in the present population, it is assumed that the presence or absence of precloacal midventral tubular supplements can be used for separation of species and constructing species-groups. Shape and length of spiculum and of gubemaculum are rather stable characters and can serve as additional differentiating characters for species.