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.

The genus Metaporcelaimus Lordello, 1965 (Nematoda, Dorylaimida, Aporcelaimidae) in Ukraine. Description of one new and one known species with granulate egg shell.

Two Metaporcelaimus species, one new and one known, are described from Ukraine. Metaporcelaimus petrophilus sp. n. is characterized by its 1.30-1.58 mm long body, lip region offset by deep constriction and 16-18 µm broad, odontostyle 15-17 µm long, neck 360-413 µm long, pharyngeal expansion occupying 47-54% of total neck length, uterus simple and 83-125 µm long or 1.6-2.7 times the corresponding body diameter, uterine eggs with granulate shell, V = 51-55%, tail conical (35-40 µm, c = 33-42, c' = 1.4-1.8 in females), spicules 43-50 µm long, and 9-13 spaced ventromedian supplements with hiatus. New data, including the first description of male specimens and SEM study, are provided for M. ovogranulosus, the Ukrainian populations of which are nearly identical to the type population from California.

The genus Metaporcelaimus Lordello, 1965 (Nematoda, Dorylaimida, Aporcelaimidae) in Ukraine: Description of one known and two new species without hiatus.

One known (M. romanicus) and two new species of the genus Metaporcelaimus, collected in natural and semi-natural habitats of Ukraine, are described and illustrated. Metaporcelaimus concinnus sp. n. is characterized by its 3.09-4.58 mm long body, lip region 16.5-19.5 µm broad and visibly wider than the adjacent body, odontostyle 17-19 µm long, neck 745-865 µm long, pharyngeal expansion occupying 62-66% of total neck length, uterus tripartite and 3.9-5.7 times the corresponding body diameter, vulva longitudinal (V = 49-53%), tail conical (44-54 µm, c = 67-94, c' = 1.0-1.3 in females), spicules 79-86 µm long with strongly bifurcate distal end, and 10-14 irregularly spaced ventromedian supplements without hiatus. Metaporcelaimus declivicaudatus sp. n. is characterized by its 2.88-3.66 mm long body, lip region 23-28 µm broad, odontostyle 24-26 µm long, neck 634-788 µm long, pharyngeal expansion occupying 48-56% of total neck length, uterus tripartite and 3.0-3.4 times the corresponding body diameter long, vulva transverse (V = 51-55%), tail conical (45-65 µm, c = 53-63, c' = 1.0-1.2) with rounded terminus, spicules 102-113 µm long, and 12-14 spaced ventromedian supplements without hiatus. New information about M. romanicus is also provided, confirming available data about this species.