The millipede family Polydesmidae Leach, 1816 (Diplopoda, Polydesmida) from Vietnam, with a description of a new cavernicolous species.

The millipede family Polydesmidae Leach, 1816 is reviewed in the scope of the Vietnamese fauna. The distribution of the species, Polydesmusvietnamicus Nguyen, 2009 is extended northward to Ha Giang Province. A new cavernicolous polydesmid, Pacidesmustuachuasp. nov., is described from two caves in northwestern Vietnam, representing the first record of the genus from Vietnam. Extensive illustrations and DNA barcodes are provided for both species, a revised key is presented to all 12 species of Pacidesmus Golovatch, 1991, as well as a key to all eight genera of Asian Polydesmidae.

A new species of Paracortina from a Vietnamese cave, with remarkable secondary sexual characters in males (Callipodida, Paracortinidae).

A new millipede species, Paracortinakyrangsp. nov., is described from a cave in Cao Bang Province, northern Vietnam. The new species is diagnosed by having an extraordinarily long projection on the head of males, reduced eyes, a gonocoxite with two processes, a long and slender gonotelopodite with two long, clavate prefemoroidal processes densely covered with long macrosetae apically, and with a distal, reverse, short spine on mesal side, and a rather sinuous distal part of the telopodite. This is the third species of the genus that is known from Vietnam. A brief comparison of some secondary sexual characters is made.

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.

Morphological and molecular characterization of Iotonchus lotilabiatus n. sp. (Nematoda: Iotonchidae) from Lao Cai Province, Vietnam.

The new species Iotonchus lotilabiatus n. sp. from Bat Xat Nature reserve in Lao Cai Province, Vietnam is described and the molecular data (18S and 28S rDNA) are given. Females of the new species are characterized by large body size (L = 3.8-5.2 mm); barrel shaped buccal cavity of large size (41-54×70-89 µm) with dorsal tooth apex located 22 to 23.5% of buccal cavity length from its base; reproductive system didelphic-amphidelphic, vagina long, corresponding almost half of body width at the vulva with distinct parrefringens vaginae, sclerotized and triangulated pieces in optical section; tail long filiform, ventrally arcuate, with three small caudal glands in tandem and prominent terminal spinneret. Males with spicules 119 to 148 µm in length, and slender, slightly curved gubernaculum, 39 to 44 µm long and with 13 to 14 ventromedian supplements. The new species Iotonchus lotilabiatus n. sp. is closest to I. miamaensis (Khan and Araki, 2002), but differs by having larger size of body length and buccal cavity, lower position of dorsal tooth apex; longer female tail with lower c but higher c' ratios and the presence of advulval cuticular structures.

A new species of a rare genus, Truxonchus quangi sp. n. (Mononchida, Anatonchidae) from bat xat nature reserve in Lao Cai Province, Vietnam.

Truxonchus quangi sp. n. is described and illustrated from Vietnam. Females of the new species are characterized by large body size (L = 4.8-5.8 mm); barrel shaped buccal cavity of large size (105-113 x 66-73 µm) with one dorsal tooth and two subventral teeth posteriorly directed, of equal shape, size and apex position; dorsal tooth apex located 36-39% of buccal cavity length from its base; reproductive system didelphic-amphidelphic, vagina long, 39-45% of corresponding body width, with distinct par refringens vaginae, sclerotized pieces rounded in optical section; tail long, filiform, ventrally arcuate, with three small caudal glands in tandem and prominent subventral spinneret. The new species is close to T. dolichurus but differs by the larger buccal cavity, more anterior position of the dorsal tooth apex, more anterior vulval position and presence of advulval pores.

Description of a new species, Actus hagiangensis (Mononchida, Mylonchulidae) from Ha Giang province, Vietnam.

Actus hagiangensis sp. nov. is described and illustrated from Vietnam. Females of the new species are characterized by medium body size (L = 1.1-1.4 mm), barrel shaped buccal cavity of medium size (26-31 x 13-15 µm) with dorsal tooth apex located 75-81% of buccal cavity length from base and two longitudinal subventral rows, each with four rasp-like denticles; reproductive system didelphic-amphidelphic, vagina short with distinct par refringens vaginae, sclerotized pieces globular in optical section; tail elongate-conoid, slightly ventrally arcuate, with three caudal glands and prominent spinneret. Male with spicules 46 µm in length, and slender, slightly curved gubernaculum, 12 µm long, without accessory piece. This is the first report of a male specimen of the genus Actus. The new species is close to A. salvadoricus but differs by the larger buccal cavity, more anterior position of the dorsal tooth apex and more rounded vaginal sclerotized pieces.