Najadicola loeiensis, Chapurina & Vikhrev & Kondakov & Tanmuangpak, 2019

Chapurina, Yulia E., Vikhrev, Ilya V., Kondakov, Alexander V. & Tanmuangpak, Kitti, 2019, A new Najadicola species (Acari: Hydrachnidia: Pionidae) from Asia, Ecologica Montenegrina 24, pp. 32-37 : 34-35

Najadicola loeiensis sp. nov.

Type material. Holotype male, “ Specimen was measured from: Bineurus exillis ( RMBH Biv 119-12) from Loei River, GPS: Loei river upstream 1, Loei Province, Thailand, 8 April 2014 (I.N. Bolotov, I. V. Vikhrev, V. M. Spitsyn, M.Yu. Gofarov) [slide no. RMBH # Hyd 119 Naj., Union.] (figures 1; 2; 3).

Type locality. Thailand: Loei River, Mekong Basin , 17.0982° N, 101.4814° E .

Etymology. The species name is derived from the type locality, the Loei River.

Host and habitat. The holotype was collected from Bineurus exillis [voucher no. RMBH Biv119-12], in the upper part of the mountain river (figure 4) .

Diagnosis. N. loeiensis sp. nov. differs from N. ingens by a smaller body size (1.8 mm vs 2.5 mm in length) and a lower value of the length to width of genital field ratio (0.73 vs 1.1). Additionally, the new species shows differences from N. ingens in the male posterior group of coxal plates (plates III and IV) (figures 2; 3). This group is in the form of a curved oval with an anterior leading edge (vs roughly trapezoidal shape of posterior coxal group in N. ingens ). The inner margin of this group is rounded (vs inner margin forming an angle in N. ingens ). The posterior margin is markedly thickened and bears a process headward laterally from the central axis of the body (vs figures of various different sources contain conflicting information: compare Koenike 1895 (one can notice a process at the image of a male) and Simmons & Smith 1984 (no process at the posterior coxal group). The apodemes of anterior coxal groups almost absent (as it has been reported for N. ingens ).

Description

Characters of the genus Najadicola (Edwards, & Vidrine 2013) : «Idiosoma weakly sclerotized with white vermiculate lines visible through the integument; no obvious dorsal plates – dorsum apparently soft; coxae in four groups; suture between third and fourth coxae incomplete; posterior apodemes of first coxa short; posterior apodemes of fourth coxa not apparent; male and female genital fields lacking central flaps and setae; genital acetabula numerous, usually 90-120 per plate; genital plates triangular and wing-like in shape in both sexes»; «legs with no swimming hairs; legs comparatively short and stocky with peg-like setae, sometimes serrated at their tips».

Measurements (in µm) of the holotype. Length including gnathosoma: 1780. Length of posterior coxal group 380 (left); width of posterior coxal group 520; genital field 310 long, 1073 wide; distance from anterior angle of first coxal plate to posterior edge of genital field 896. Dorsal lengths of segments of pedipalp: Tr 91, Fe 239, Ge 121, Ti 226, Ta 111. Dorsal lengths of leg segments: leg I: Tr 115, BFe 211, TFe 127, Ge 187, Ti 227, Ta 209; leg II: Tr 147, BFe 155, TFe 133, Ge 189, Ti 223, Ta 228; leg III: Tr 170, BFe 145, TFe 160, Ge 223, Ti 266, Ta 261; leg IV: Tr 181, BFe 156, TFe 158, Ge 258, Ti 321, Ta 285. Ratios: ratio of length to width of posterior coxal group 0.73; ratio of width to length of genital field 3.46.

Total number of acetabula on both genital plates is 212: 113 acetabula on one plate and 99 acetabula on the other (figure 3).

Distribution. Known only from the type locality in the Loei River, Mekong Basin, Thailand.