Rhysida vietnga, Le & Do & Tran & Nguyen, 2025

Rhysida vietnga sp. nov.

Figs 1 View Figure 1 , 8 View Figure 8 , 9 View Figure 9

Examined materials.

Holotype: Vietnam • 1 specimen; Lao Cai Province, Hoang Lien NP , mixed bamboo forest; 22.4156°N, 103.77778°E; 1,529 m a. s. l.; 15 Apr. 2019; H. D. Nguyen leg.; HLS.064 . GoogleMaps

Paratypes: • 2 specimens; same location; 22.4156°N, 103.77778°E; 1,529 m a. s. l.; 15 Apr. 2019; S. X. Le & H. D. Nguyen leg.; HLS.006 , HLS.092 GoogleMaps ; • 2 specimens; Son La Province, Ta Xua NR , mixed bamboo forest; 21.35722°N, 104.67333°E; 726 m a. s. l.; 11 Oct. 2017; S. X. Le & H. T. Vu leg.; TX.D4.002 , TX.D4.003 ; 1 specimen GoogleMaps • same location; natural forest; 21.35972°N, 104.66972°E; 722 m a. s. l.; 30 May 2018; H. D. Nguyen leg.; TX.258 GoogleMaps .

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.

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 View Figure 8 ). 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 View Figure 8 ).

Forcipular segment (Fig. 8 B View Figure 8 ), 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 View Figure 8 , 9 A View Figure 9 ).

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 View Figure 8 , 9 B View Figure 9 ).

Coxopleuron densely covered by pores (except the apical part); coxopleural process with 2 apical and 1 lateral spine, without dorsal spine (Fig. 9 B View Figure 9 ).

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 View Figure 9 ).

Variations.

Body length reaches a maximum of 66 mm ( TX.D4.002 ). Specimens from Ta Xua NR ( Son La) show that the lateral margination starts from tergite 5 ( TX.258 ) or tergite 6 ( TX.D4.003 ). The keels on the tergites from specimen TX.D4.002 present on tergites 12–20. Locomotory legs with tibia spines from legs 1–4 or legs 1–6 ( HLS.092 ). Prefemoral spines on ultimate leg can have 3–4 VL, 2–3 VM, 3–4 M, and 1–4 DM spines.

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.

Remarks.

The new species differs from R. immarginata in the clearly visible but incomplete lateral margins on the tergites (absent in R. immarginata , except for tergite 21). The absence of a paramedian suture on the sternites is a distinguishing feature that separates the new species from Alluropus calcaratus . Rhysida vietnga sp. nov. is distinguished from R. longipes and R. lithobioides by the presence of keels on the tergites. This is also a character to distinguish the new species and its congeners.

Rhysida vietnga exhibits morphological similarities to Rhysida singaporensis Verhoeff, 1937 , particularly in the distinctive structure of the dorsal plate with keels. This characteristic also distinguishes these two species from other members of the genera Rhysida and Alluropus . Therefore, a morphological comparison between the new species R. vietnga and R. singaporensis is most appropriate. The distinction between these two species can be made based on the following characters: The new species, based on six specimens examined in this study, is markedly smaller than R. singaporensis , with a maximum body length of 66 mm and an average of 43 mm, whereas R. singaporensis typically ranges from 73 to 89 mm in length. According to descriptions of Lewis (2001) and Siriwut et al. (2018), R. singaporensis has a median keel on the tergites, while the lateral longitudinal keels are either not mentioned or described as short (incomplete); if present, longitudinal keels end with numerous spines. However, the illustrations in these studies do not show the presence of complete longitudinal keels. In contrast, R. vietnga has 5–7 distinct, complete longitudinal keels on tergites 8–20 (similar to those of Otostigmus scaber ; see Lewis 2001, p. 26, fig. 49), along with abundant spinulation scattered across the tergites, which becomes more pronounced on the posterior tergites (Fig. 9 A View Figure 9 ). The comparative morphological data for Southeast Asian species are summarized in Table 1 View Table 1 .

In addition, R. singaporensis is distributed in the archipelagic region, likely limited to the Malay Archipelago, while R. vietnga is found in the mainland area of the Indochina Peninsula.

Distribution.

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