Tylencholaimus helanensis, Wu, Wen-Jia, Yu, Lu, Xie, Hui, Xu, Chun-Ling, Yu, Jiao & Wang, Dong-Wei, 2018

Wu, Wen-Jia, Yu, Lu, Xie, Hui, Xu, Chun-Ling, Yu, Jiao & Wang, Dong-Wei, 2018, Description and molecular analysis of Tylencholaimushelanensis sp. n. from China (Dorylaimida, Tylencholaimidea), ZooKeys 792, pp. 1-14 : 3-5

Tylencholaimus helanensis sp. n. Figs 1, 2

Material examined.

Seven females from Qinghai Province; 38°40.311'N, 105°50.905'E; 22 August 2014; collected by Dong-Wei Wang, Wen-Jia Wu, Lu Yu, and Hui Xie. Female holotype (M51.B.a) and six female paratype specimens (slide numbers: M51.A.a, b, c, d, e and M51.B.b) are deposited in the Lab of Plant Nematology/Research Center of Nematodes of Plant Quarantine, South China Agricultural University, Guangzhou, Guangdong 510642, China.

Descriptions.

Female. Body robust and cylindrical, tapering towards the anterior end. Habitus variable, almost straight or slightly twisted after fixation. Cuticle two layers, 1.0-2.0 μm thick in anterior region, 1.5-2.5 μm at mid-body, and 2.5-3.5 μm on tail; outer layer with fine transverse striations, the inner one loose and often shrunken after fixation. Lateral chord occupying about one-third of the body diameter at mid-body, lateral pores indistinct. Lip region cap-shaped, offset from the body by a constriction, 2.4-2.8 times as wide as high or 25% in average of the body diameter at posterior end of the neck region wide. Lips not amalgamated, the outer part of each lip not distinct from the inner one. Labial and cephalic papillae distinct but not interfering with the contour. Amphidial foveae cup-shaped, opening at the level of the constriction, apertures 0.4 times on average as wide as the lip region. Odontostyle straight with a distinct lumen, 8-9.5 μm long, 0.9-1.0 times as long as the lip region width, its aperture about one-third of its length. Odontophore rod-like with small basal knobs, 9-11 μm long, 1-1.3 times as long as the odontostyle. Guiding ring single. Nerve ring situated at 35-42% of the neck length. Anterior part of pharynx slender and expanded gradually, basal expansion occupying 39-43% of the total neck length. Pharyngeal gland nuclei locations ( Andrássy 1998) are as follows: D = 60-66%, AS1 = 21-30%, AS2 = 36-44%, PS1 = 62-74%, PS2 = 67-79%. Cardia short, conoid to rounded. Genital system didelphic-amphidelphic. Ovary reflexed, the anterior one 67-86 μm and the posterior one 54-79 μm long. Each oviduct consists of a wider pars dilatata and a slender part, 0.9-1.3 times the uterus long; anterior oviduct 83-107 μm and the posterior one 61.5-92 μm long. Sphincter present at the junction of oviduct and uterus. Uterus simple and with a wide lumen, the anterior one 66-85 μm and the posterior one 58-72 μm long. Vulva transverse. Vagina showing ‘+’ shape in ventral view, extending 44.5-46% inwards the corresponding body width. The walls of pars proximalis vaginae recessed inward in the middle, making pars proximalis vaginae violin-shaped, 12-13 μm long and 13-15 μm wide, with poorly developed musculature surrounding only the part adjacent to pars distalis vaginae. Pars refringens lacking, pars distalis vaginae 7 μm long. No sperm observed in the genital system. Prerectum 2.4-4.2 times and rectum 0.9-1.2 times the body diameter at anus level. Tail hemispheroid with blunt rounded to flat terminus. One caudal papilla opening in tail terminus.

Fore measurements see Table 1. The male was not found.

Sequence and phylogenetic analysis.

The sequences of 18S rDNA and D2-D3 region of 28S rDNA of Tylencholaimus helanensis sp. n. were obtained. The inter-individual variabilities of the 18S rDNA sequences and the 28S rDNA sequences are one gap and two base pair differences, respectively. Two sequences for each of the genes were deposited in GenBank (accession numbers: KU992903 (1746 bp long) and KU992904 (1747 bp long) for 18S rDNA, KU992905 and KU992906 (both 840 bp long) for D2-D3 region of 28S rDNA). The BLAST search for the 18S rDNA showed the highest similarity (94% and 95%) to the sequence of an unidentified species of Tylencholaimus (AJ966510). For the D2-D3 region of 28S rDNA, both sequences showed the highest similarity (79%) to the sequences of Xiphinema brevicollum Lordello & Da Costa, 1961 (AY580057). In the 18S rDNA phylogenetic reconstructions (Fig. 3), the new species is in a 100% supported clade with T. teres and T. proximus . And in the D2-D3 region of 28S rDNA phylogenetic reconstructions (Fig. 4), the new species is in a clade with an unidentified species of Tylencholaimus with 90% posterior probability.

Type habitat.

Rhizosphere soil of unidentified grasses from Helan Mountain, Alxa Left Banner, Alxa League, Inner Mongolia, China.

Etymology.

The new species is named after the mountain Helan, which is a famous mountain with a wealth of human history including rock paintings, architecture, vineyards, and a national park.

Diagnosis and relationships.

Tylencholaimus helanensis sp. n. is characterized by having a body length of 0.93-1.07 mm; body tapering towards the anterior end; lip region offset from the body by a constriction and 25% in average of the body diameter at posterior end of the neck region wide; amphid aperture 0.4 times in average as wide as the lip region; odontostyle 8-9.5 µm long and 0.85-1.0 times as long as the lip region width; odontophore 1-1.3 times as long as the odontostyle; basal expansion of pharynx 39-43% of the total neck length; female genital system didelphic-amphidelphic; vulva transverse; prerectum 2.4-4.2 times and rectum 0.9-1.2 times the body diameter at anus long; tail hemispheroid with blunt rounded to flat terminus; males not found.

Tylencholaimus helanensis sp. n. is close to T. congestus Loof & Jairajpuri, 1968, T. cosmos (Dhanam & Jairajpuri, 1999) Peña-Santiago, 2008, T. crassus Loof & Jairajpuri, 1968, T. paracrassus Monteiro, 1970, T. sinensis Li, Baniyamuddin, Ahmad & Wu, 2008 and T. teres Thorne, 1939 in having a body length about 1 mm or less, female genital system didelphic-amphidelphic, odontostyle less than 10 μm and ‘V’ value less than 62 in average, but can be differentiated by having panduriform pars proximalis vaginae. In addition, the new species differs from T. congestus ( Loof and Jairajpuri 1968; Peña-Santiago and Coomans 1994a) by having longer body (0.93-1.07 mm vs. 0.72-0.83 mm), lower ‘a’ value (a = 24.8-27.5 vs. 29-33), different lip region (lip region cap-shaped, lips not amalgamated and no inner liplets vs. lips apparently separated, inner part protruding and forming liplets), absence of large cells in the vaginal area (vs. presence) and oviducts 0.9-1.3 (vs. 3-4) times the uterus long. From T. cosmos ( Dhanam and Jairajpuri 1999; Ahad and Ahmad 2016), the new species differs by having longer pharynx and basal expansion (216-237 μm vs. 146-207 μm; 87-102 μm vs. 61-87 μm, respectively), and sphincter present at the junction of oviduct and uterus (vs. uterus and oviduct without distinct sphincter differentiation). From T. crassus ( Loof and Jairajpuri 1968; Peña-Santiago and Coomans 1994a) by longer body (0.93-1.07 mm vs. 0.68-0.92 mm), smaller lip region (9.5-10 μm vs. 10.5-12 μm wide; 3.5-4.0 μm vs. 5-5.5 μm high), absence of postrectal blind sac (vs. presence) and tail hemispheroid with blunt rounded to flat terminus (vs. convex conoid with rounded tip). From T. paracrassus ( Peña-Santiago and Coomans 1994a), the new species can be differentiated by having narrower lip region (9.5-10 μm vs. 11.5-13 μm wide), shorter odontostyle (8-9.5 μm vs. 10-11.5 μm), longer prerectum (71-100 μm vs. 47-66 μm), tail hemispheroid with blunt rounded to flat terminus (vs. convex conoid with rounded tip) and males absent (vs. present). It differs from T. sinensis ( Li et al. 2008) by lip region one-fourth (vs. one-third) of the body diameter at posterior end of neck region, longer odontostyle and odontophore (8-9.5 μm vs. 7 μm; 9-11 μm vs. 8 μm, respectively), longer pharynx and basal expansion (216-237 μm vs. 191-208 μm; 87-102 μm vs. 67-75 μm and ocuupying 39-43% vs. 35-36% of the total neck length, respectively), much longer oviducts (anterior one 83-107 μm vs. 53-63 μm and the posterior one 61.5-92 μm vs. 45-50 μm long), prerectum 2.4-4.2 (vs. about 5) times the body diameter at anus long, longer rectum (22-28 μm vs. 18-20 μm). From T. teres ( Loof 1971; Thorne 1974; Vinciguerra 1986; Peña-Santiago and Coomans 1994a), it differs by the females having lip region one-fourth in average (vs. one-third) of the body diameter at posterior end of the neck region, odontostyle longer (8-9.5 μm vs. 5-6 μm), one caudal opening in tail terminus (vs. one pair of subterminal pores), the anterior and posterior genital branch equally developed (vs. the anterior branch more developed than the posterior one), no sperm observed in the genital tract and males not known (vs. sperm present along the entire genital tract and males as frequent as females).