Tad E-tu Waterfall, Bolaven Plateau, Pakse, Champasak, Laos (15°13'10.6"N, 105°55'31.3"E) (Fig. 54B).

Holotype CUMZ 00316, adult specimen from type locality (Fig. 54A). Paratypes CUMZ 00317, one adult, Tad-Yueang Waterfall, Mueang Singh, Luang Namtha, Laos (15°09'55.1"N, 106°06'10.6"E). NHMUK 010305528, one adult, Kao Sok National Park, Surat Thani, Thailand, labeled as “a distinct population of Scolopendra subspinipes but without paramedian sutures on the tergites”, det. J.G.E. Lewis, leg. G. Beccaloni, 2001. NHMUK 1928.5.30.7, one adult, Bac-Kan, Vietnam, labelled as “Scolopendra subspinipes”. NHMUK 1928.5.30.6, one female, Dac-To, Annam [Vietnam], Delacour-Lowe expedition.

From “cataract”, meaning waterfall, for the type locality at Tad E-tu Waterfall.

18–19 antennal articles, 6 basal articles glabrous dorsally. Cephalic plate punctate. 5–6 teeth on tooth-plate. Tergites 7(14)-20 with paramedian sutures, all incomplete, present only on anterior and posterior parts. Tergite of ultimate leg-bearing segment without depression or suture. Paramedian sutures confined to anterior 15–20% of sternites. Coxopleural process with 1–3 apical+subapical spines, 0–1 dorsal spine, without lateral spine. Ultimate leg prefemora with 1–2 VL, 1–2 M, 0–2 DM and prefemoral process with 1–3 spines. Tarsal spur on legs 1–19(20).

(variation of paratypes is given in parentheses). Body length 12.8 cm (up to ca. 20 cm long in paratype NHMUK 1928.v.30.6). Blackish colouration on entire body. Cephalic plate and segments monochromatic. Tergites dark greenish or black. Cephalic plate without small punctae on anterior part; median sulcus present. Posterior part of cephalic plate without paramedian sulci.

Antenna usually with 19 articles (atypically with 18 articles on one side), basal 6 glabrous dorsally (Fig. 57A), 5–5.5 glabrous ventrally. Antennae reach segment 4(5). Forcipular trochanteroprefemoral process with denticles in two groups, one apical tooth and (2)3–4 inner (Fig. 57C). Tooth-plates (Fig. 55A–B) wider than long or nearly as long as wide, with 6 teeth (5 in NHMUK 1928.5.30.6). Tooth-plate with straight, transverse basal suture. Coxosternal surface smooth, without median suture (Figs 55D, 57D). Article 2 of second maxillary telopodite with spur.

Anterior margin of T1 underlying cephalic plate (Fig. 55C). Incomplete paramedian sutures on all tergites; margination typically starting on T7 (TT10–14). Tergite surface (Figs 56A, 57B) smooth, with median sulci starting from TT5–20. Tergite of ultimate leg-bearing segment (Figs 56B, 58B) curved posteriorly, without median furrow or depression; ratio of width: length of tergite of ultimate leg-bearing segment 1.1:1. Anterior part of sternites (Figs 55E, 57E) with short paramedian sutures confined to approximately 20–45% length of sternite. Surface of sternites smooth. Sternite of ultimate leg-bearing segment (Figs 56C–D, 58C–D) with sides converging posteriorly; surface without depression. Pore-field on coxopleuron extending to and overlapped by margin of tergite of ultimate leg-bearing segment, dorsal margin of pore area sinuous, most elevated anteriorly (Figs 56F, 58A).

Coxopleural process (Fig. 56C–D) moderately long or short with 2–3 apical+subapical spines (spines atypically absent on one side; CUMZ 00317), without lateral spine (one paratype with one dorsal spine on one side: CUMZ 00317). Pore-free area extending 30–90% length from distal part of coxopleural process to margin of sternite of ultimate leg-bearing segment (Figs 54C, 56C–D and 58C–D.).

All legs without setae and tibial spur. One tarsal spur on legs 1–20 (1–19 in one paratype, CUMZ 00317). Ultimate leg: long and slender, with ratios of lengths of prefemur and femur 1.1:1, femur and tibia 1.1:1, tibia and tarsus 2 1.3:1; tarsus 1 and tarsus 2 1.9:1. Prefemora flattened dorsally with acute blackish spines. Prefemoral spines (Figs 56G–H, 58C, 58E): 2 VL, 1 M, 0–1 DM, prefemoral process with 2 spines (Paratypes: 1–2 VL, 1–2 M, 0–2 DM and prefemural process with 1–3 spines).

Genital segments well developed (Figs 28C–D, 54C), reaching longer than distance between posterior margin of sternite of ultimate leg-bearing segment and distal part of coxopleural process. Sternite of genital segment 1 round and convex posteriorly, with median suture. Tergites of genital segment lacking small setae. Presence of gonopods and penis uncertain because genitalia are mostly retracted in holotype and paratypes; only two female specimens show genital segments (NHMUK 010305528 and 1928.5.30.6).

The paratype collected in Thailand in 2001 (NHMUK 010305528) was observed to display apparent amphibious habits. The following account is based on observations by G. Beccaloni (pers. comm., Jan. 2016). The centipede was initially observed under a rock slab beside a stream ca. 1.5 m wide and 20 cm deep. It escaped into the stream and concealed itself under a rock. After extraction from the stream it was placed in a glass container of water, in which it swam powerfully on the bottom of the container with vigorous horizontal undulating motions.

This species exhibits an atypical characteristic for scolopendromorphs, namely incomplete paramedian sutures on the tergites. Very few members in only three genera share this character, these being within Scolopocryptops Newport, 1844, Scolopendra and Rhysida Wood, 1862. Within Scolopendra, only two described species, Scolopendra hainanum from Hainan Island, China, and “Scolopendra subspinipes piceoflava” (treated above as a synonym of Scolopendra subspinipes following Kronmüller (2012)), from Sulawesi, Indonesia, have been reported to lack or have nearly absent paramedian sutures on the tergites. Scolopendra cataracta and “Scolopendra subspinipes piceoflava” can be distinguished from each other by: paramedian sutures confined to the posterior part of tergites in Scolopendra cataracta vs complete sutures in “Scolopendra subspinipes piceoflava”, very short paramedian sutures on the sternites vs sutures extending along 80–100% the length of the sternites, and three apical/subapical spines on the coxopleural process vs one or two.

Scolopendra cataracta differs from Scolopendra hainanum by the short paramedian sutures on the sternites versus being nearly complete in Scolopendra hainanum, the number of spines on the coxopleural process (three vs one or two), and the number of VL spines on the ultimate leg prefemora. The two species can also be distinguished by their colouration patterns and their distributions, though the latter are closely associated. For these reasons, we regard Scolopendra cataracta as distinct from Scolopendra hainanum, and its sampled populations group as monophyletic for each partial gene analysis (see Table 11 for morphological comparison). It is likewise morphologically distinct from Scolopendra subspinipes, Scolopendra multidens and Scolopendra dawydoffi. DNA sequences are not available for Scolopendra hainanum but would be useful to study the relationship between these two apparently related species.

All localities are in mainland territory. The currently known distribution (Fig. 29) is as follows: Southeast Asia: Laos (Champasak and Luang Namtha), Thailand (Surat Thani) and Vietnam (Bac Kan and Dac-To).