Rhysida vietnga

Description. Body length 58 mm. Antennae composed of 21 articles, of which three basal ones glabrous dorsally, following segments densely covered by minute setae (Fig. 8 A, B). Antenna length reaching to 6 th body segment. Cephalic smooth, without puncta and setae; lateral and posterior margination absent, the posterior border adjacent to anterior border of tergite 1. Four big ocelli present, nearly equal in size. The median suture on the top of cephalic plate long, shallow (Fig. 8 A). Forcipular segment (Fig. 8 B), coxosternite, trochanteroprefemora, and the basal part of tarsungulae smooth, without punctate and setae; coxosternite without median suture. Tooth-plates slightly wider than high and nearly semicircular, with 5 short teeth and well chitinized; the distance between the tooth – plates wide; each tooth-plate with straight, transverse basal suture. Forcipular trochanteroprefemoral process bearing 3 short denticles, the latter being indistinct, position of denticles higher than tooth – plates. Maxillae with sparse short setae, and segment 2 of second maxillary telopodite with spur; chitin-line very short. Tergites with very small punctae; lateral margination incomplete on tergites 9 – 20 and complete on tergite 21; paramedian sutures absent on all tergites; tergites 1 – 7 smooth, and tergites 8 – 20 with 5 – 7 keels and many spinulations which scattered on tergites, more obvious in the posterior tergites; tergite of ultimate leg-bearing segment sub-quadrangular and convex posteriorly (Figs 8 D, 9 A). Sternite surface smooth (without punctae), lacking any median sulci. Sternites shield-shaped, last sternite trapezoid (or nearly triangular). Incomplete paramedian suture on anterior part of some sternites (<10 % of their width) or absent, lacking depression (Figs 8 B, C, 9 B). Coxopleuron densely covered by pores (except the apical part); coxopleural process with 2 apical and 1 lateral spine, without dorsal spine (Fig. 9 B). Locomotory legs usually bearing small, short setae; legs 1 – 4 with 1 tibia spur, legs 1 – 18 with 2 tarsal spurs, 19 – 20 with 1 tarsal spur. Ultimate legs very thin and long; the ratio of lengths of prefemur, femur, tibia, tarsus 1, and tarsus 2 as follows: 2.8: 2.7: 2.5: 2.0: 1.0; ratio of length and width of prefemur 6: 1. Prefemoral spines on ultimate leg: 4 VL, 3 VM, 3 M, and 1 DM spines; prefemoral process of ultimate legs very short with 1 spine; all of segment smooth (Fig. 9 C).

Figs 1, 8, 9

Diagnosis. Body with 21 leg-bearing segments. LBS 7 th with spiracles. Antennae composed of 18 articles, of which three basal ones glabrous dorsally. Tooth-plate with five short teeth. Tergites with lateral marginations and 5 – 7 keels and many spinulations scattered on tergites, more obvious in the posterior tergites, without complete paramedian sutures. Sternites with paramedian suture incomplete on anterior part (on some sternites). Coxopleural process with 2 apical, 1 lateral spines and without dorsal spine.

Distribution. Only known in Lao Cai province and Son La province in Vietnam (Fig. 2).

Etymology. The species name is named after the Joint Vietnam-Russia Tropical Science and Technology Research Center (VRTC), an institution that has significantly contributed to biodiversity research in Vietnam.