Descriptions of two new and one known species of Parkellus Jairajpuri, Tahseen and Choi, 2001 (Nematoda: Mononchidae) and their phylogenetic position among Mononchida

Two new species of Parkellus (Jairajpuri et al., 2001) from Vietnam and a population of Parkellus zschokkei (Ahmad and Jairajpuri, 2010; Menzel, 1913) from Ukraine are described, illustrated and their phylogenetic position among the Mononchida is presented. The molecular data (18S and 28S rDNA) are given for the three investigated species – first time for the genus Parkellus. Parkellus hagiangensis sp. nov. is characterized by a medium-sized buccal cavity, posterior position of the dorsal tooth located below the beginning of the pharynx, males having the ventromedian cuticular pores above and below the excretory pore, short spicules with conical proximal part; females with very faint pars refringens vaginae and small teardrop-shaped pieces, short pars distalis vaginae, the presence of small ventromedian vulval papillae. Parkellus tuyenquangensis sp. nov. is characterized by a medium-sized buccal cavity, posterior position of the dorsal tooth located above the beginning of the pharynx, males having the ventromedian cuticular pores above and below the excretory pore, medium-sized spicules with a cylindrical proximal part, very short lateral guiding pieces, females with very strongly sclerotized pars refringens vaginae, medium size teardrop-shaped pieces, short pars distalis vaginae thickened at the junction with pars refringens vaginae. The newly described species are morphologically most similar to P. parkus and P. zschokkei. An identification key to Parkellus species is presented.