(Fig. 5A). Pa’ Ramudu River (a tributary of Pa’ Kelapang River), 3°32'16.2"N, 115°30'22.5"E, ca 900 m a.s.l.; meandering, 7–15 m wide, shallow, slowly flowing through a degraded primary forest; environment of Kampung Ramudu, Kelabit Highlands, Sarawak, Malaysia.

Holotype ♂ [JK147] (CFDS): “Malaysia, Sarawak, Miri distr., Ramudu env., 5.03.2019, (No. 51), 3°32'16.2"N, 115°30'22.5"E, ca. 900 m a.s.l., Ramudu riv., J. Kodada & D. Selnekovič lgt.”. Paratypes (CFDS, CKB, NMW): 10 ♂♂ [incl. JK146], 4 ♀♀ [incl. JK144, JK145]: same label data as holotype; 3 ♂♂, 4 ♀♀: “Malaysia, Sarawak, Miri distr., Ramudu env., 5.–6.03.2019, (No.50), Pa’ Masia riv., 3°31'57.1"N, 115°30'41.4"E, ca. 970 m a.s.l., J. Kodada & D. Selnekovič lgt.”; 1 ♀: “Malaysia, Sarawak, Miri distr., Ramudu env., 28.06.2018, (18) 03°32'50.8"N, 115°29'25.9"E, 920 m a.s.l., Pa’ Kasi riv., J. Kodada & D. Selnekovič lgt.”.

Ancyronyx lianlabangorum sp. nov. represents one of the largest species characterized by: (1) large size: body length ca 2.5–3.0 mm and elytral width ca 1.3–1.4 mm; (2) comparatively short obovate body form; (3) shiny black head and unicolored yellow pronotum; (4) black-yellowish color pattern of elytra with moderately prevailing black; (5) femora yellowish around middle, lacking dark spot; (6) aedeagus large, with subparallel-sided, apically abruptly narrowed penis; parameres robust, shorter and reaching only up to apical third of penis length, apices wide and emarginate near middle; (7) ovipositor robust, with numerous conspicuous peg-like sensilla; stylus moderately long: ca 0.43× as long as distal portion of coxite; distal part of coxite short and wide: 1.16× as long as wide at middle; longitudinal baculum of paraprocts about twice as long as coxite.

The morphologically most similar A. pulcherrimus can be distinguished by: (1) distinctly smaller size: body length ≤2.0 mm and elytral width ≤0.9 mm; (2) subparallel-sided elongate body form; (3) bicolored head and pronotum; (4) black-yellowish color pattern of elytra with moderately prevailing yellow; (5) femora with dark spot near middle; (6) smaller aedeagus with sides of penis subparallel in basal half and gradually tapering in apical half; parameres long, nearly reaching tip of penis, apices subtruncate and wide; (7) ovipositor slender, with fewer conspicuous peg-like sensilla; distal portion of coxite longer and thinner: 1.8× as long as wide at middle; longitudinal baculum of paraprocts ca 1.6× as long as coxite; (8) about 17% divergence of the partial mtDNA for cytochrome c oxidase subunit COI.

Ancyronyx reticulatus, the second similar species, differs from the new species in: (1) distinctly smaller size: body length ≤2.1 mm and elytral width ≤0.9 mm; (2) subparallel-sided elongate body form; (3) bicolored head and pronotum; (4) black-yellowish color pattern of elytra usually with moderately prevailing yellow; (5) surface of elytra and metaventral disc matt, reticulate; (6) smaller aedeagus with sides of penis subparallel along basal half and gradually tapering in apical half; parameres long, nearly reaching tip of penis with apices truncate; (7) ovipositor shorter, with fewer conspicuous peg-like sensilla; stylus longer compared to length of distal portion of coxite; longitudinal baculum of paraprocts ca 1.6× as long as coxite.

Ancyronyx helgeschneideri Freitag & Jäch from Palawan (Philippines) is also quite similar, but differs from the new species in: (1) distinctly smaller size: body length ≤2.0 mm and elytral width up to 0.9 mm; (2) elongate-oval body form; (3) bicolored head and pronotum; (4) elytral color pattern with moderately prevailing dark brown; (5) elytral surface rugulose; (6) distinctly smaller aedeagus with conically tapering penis; parameres long, nearly reaching tip of penis with obliquely truncate apices; (7) ovipositor shorter, stylus and distal portion of coxite relatively longer; longitudinal baculum of paraprocts ca 1.3× as long as coxite.

Body form obovate, with rather typical, narrowed “flightless” appearance; elytra strongly convex dorsally, with the highest point at anterior 0.43; BL: 2.97 mm, EW: 1.37 mm, BL/EW: 2.17.

Coloration (Fig. 3A). Labrum black with brownish anterior margin; mandibles dark brown, remaining mouth parts and antennae yellow, except apically darkened terminal antennomere; cranium black dorsally, yellow ventrally; pronotum yellowish; scutellum brownish. Elytra bicolored; anterior half dominantly black with small yellowish spot on humeri and a large central yellowish spot reaching laterally up to the third stria and from anterior fourth up to slightly behind mid-length of the elytra; central spot extending laterad up to margins and posteriad toward apices; thus, the black preapical mark is anchor-shaped. All anepisterna, epimera and lateral portions of metaventrite black; coxae yellow; femora yellowish except small black apical portion; tibiae dark in proximal 0.4 and near articulation with tarsi, yellowish in distal portions; tarsomeres 1–2 darker, tarsomeres 3–5, and claws yellowish brown.

Figure 3. 

Ancyronyx lianlabangorum sp. nov. A holotype, dorsal view, body length 2.97 mm B female paratype, dorsal view, body length 2.97 mm C holotype, dorsal view of body D holotype, ventral view of body E brachypterous paratype with removed elytron, dorsal view, body length 2.98 mm.

Figure 4. 

Ancyronyx pulcherrimus A male from Gunung Mulu NP, body length 1.82 mm B brachypterous male from Gunung Mulu NP, dorsal view (left elytron and apical segments of abdomen removed), body length 1.92 mm C male from Bayur River, dorsal view, body length 1.70 mm D male [JK106] from Bayur River, dorsal view, body length 1.70 mm.

Head. Labrum about as long as clypeus, anterior margin slightly concave, almost straight; bipunctate: larger punctures deeper and with fine setae, smaller punctures dense and very shallow, thus surface appearing microreticulate (visible at a magnification of 160×). Clypeus wide, extremely finely punctate-reticulate on anterior half, smooth and shiny on posterior half. Frons and vertex irregularly punctate, punctation more distinct on central portion, punctures intermixed with flat shiny tubercles; frontoclypeal suture almost straight, extremely finely impressed; surface deeply impressed around antennal insertions. Eyes large, subellipsoidal in lateral view, strongly protruding near middle; ratio of horizontal/vertical eye diameter: 1.36. Antennae 11-segmented, about as long as pronotum; each antennomere with a few scattered trichoid setae; antennomeres 9–11 each with two clusters of peg-like setae near distal margins; terminal segment with additional different sensilla. Ratio of length of antennomeres 1–11: 0.09: 0.09: 0.07: 0.05: 0.05: 0.05: 0.05: 0.07: 0.07: 0.07: 0.17 mm. Gena microsculptured; gula narrow, smooth; gular sutures very fine, but discernible; posterior tentorial pits deep and large. HW: 0.66 mm; ID: 0.38 mm.

Thorax. Pronotum (Fig. 3C) distinctly broader than long, PL/MW: 0.76, PL: 0.87 mm, MW: 1.15 mm, widest near posterior angles; anteriorly attenuate; anterior margin strongly arcuate, bordered by narrow protruding translucent edge; hypomeral portion almost entirely visible in dorsal view; anterior transverse groove distinctly impressed, forming a widely open “V”; area posterior of transverse groove strongly gibbous and distinctly higher than anterior portion; mesal longitudinal carina absent; posterolateral oblique grooves shallow, hardly discernible. Pronotal surface with irregularly arranged, flat shiny, sometimes cordiform tubercles, each of which bears a short seta; tubercles in anterior transverse groove dense and coalescent (forming a nearly rasp-like structure), laterad and posteriad gradually smaller and less densely arranged. Prosternum irregularly densely and roughly punctate, very short in front of procoxae; anterior margin strongly concave, unusually thickened; prosternal process distinctly transverse, about as wide as head, depressed near apex, sides slightly sinuate; posterior margin widely rounded, feebly protruding posteriad. Scutellum subpentagonal, smooth and shiny. Elytra (Fig. 3C) moderately elongate and only somewhat wider than pronotum, EL: 2.10 mm, EW: 1.37 mm; convex in lateral view, with highest point at anterior 0.43; lateral sides visible in dorsal view; lateral outline slightly narrowed at level of metacoxae, then gradually convergent towards conjointly rounded apices; elytral punctures forming ten more or less regular rough rows; seven rows between suture and shoulder including accessory scutellary striole (five punctures); punctures large, round to subquadrate and deeply impressed on disc and laterally, smaller and less distinct posteriorly; interstices and intervals very narrow and moderately raised on disc and laterally, posteriorly becoming wider and flatter; surface shiny with sparse short setae and some longer trichoid setae (partly abrased); humeri small but prominent. Lateral rim visible from above, not serrate, finely carinate, positioned at abdominal recess of laterosternites and laterally produced margin of ventrites, very tightly fitted to abdomen. Mesoventrite approximately half as long as prosternum; mesoventral cavity deep and robust; surface strongly and irregularly punctate; without mesoventral discrimen; posterior angles rounded and moderately protruding, raised and partially concealing mesocoxae; mesepimeron small, protruding laterad into short blunt process visible in dorsal view. Metaventrite (Fig. 3D) along midline about as long as combined length of prosternum and mesoventrite; anterior margin arcuate, anterior portion declined; disc with deep wide longitudinal depression mesally, discrimen finely raised, metakatepisternal suture fine; surface densely irregularly roughly punctate, punctures coarser and denser laterally. Hind wing distinctly shorter than elytron, unfunctional, reduced in length and venation (Fig. 3E). Forelegs very long, about 1.73× as long as body; pro- and mesocoxae large and prominent, strongly protruding laterally at least partially visible in dorsal view, bluntly drop-shaped; metacoxae smaller and less protruding laterally. Femora and tibiae with short setae and characteristic pattern of smooth, shiny elongate flat tubercles; tibiae with a few longer setae; distal tarsomeres with several longer setae near apex; claws large, strongly curved, base with three teeth, two larger ones and a smaller one.

Abdomen (Fig. 3D). Intercoxal process moderately longer than length of first ventrite posterior of metacoxae, anterior margin very wide, arcuate; anteromedial portion on same level with bottom of metaventral depression; rows of deep punctures arranged along anterior margin; ratio of length of ventrites 1–5: 0.37: 0.23: 0.23: 0.18: 0.30 mm. Surface of ventrites 2–5 with sparse punctures and flat setiferous, almost cordiform tubercles; punctures more distinct on medial area; tubercles more prominent and more conspicuous laterally; fifth ventrite densely tuberculate.

Sternite IX ca 600 μm long and very robust (Fig. 7B); apical margin moderately arcuately emarginate; lateroapical portion with a few moderately long setae and numerous microtrichia; paraprocts not reaching beyond apical margin; ventral strut short and wide. Tergite VIII with complete transverse sinuate ridge dividing anterior and posterior portion, anterior surface with dense microtrichia; sides subparallel along basal half and arcuate in apical half; surface with sparse hair-like setae, which are more robust and longer on sublateral portions than along lateral margins.

Aedeagus (Fig. 6A–C) ca 600 μm long; penis including lateral basal apophyses ca 2.4× as long as phallobase, robust and well sclerotized, sides subparallel, short apical portion abruptly narrowed and moderately curved ventrad (lateral view), dorsolateral portion with numerous shorter setae; apex widely rounded; basal apophyses long; ventral sac large; fibula conspicuous and long, moderately wide; dorsal portion mesally with unusual, more distinctly pigmented/sclerotized longitudinal structure (similar to fibula); surface of endophallus with spinules; corona distinct. Phallobase asymmetrical. Parameres robust and wide, reaching apical third of penis, broadest near base, narrowest near middle; dorsal and ventral outline moderately concave; apices wide, rounded and emarginated in middle, appearing nearly double-peaked (in dorsal/ventral view); apical and lateral surface of parameres with short setae.

Tergite VIII with strong complete transverse sinuate ridge; anterior portion with dense microtrichia; posterior portion more distinctly pigmented, with two sublateral clusters of strong conspicuous hair-like setae; lateral sides arcuate; apical margin with protruding translucent edge. Sternite VIII robust, median strut short and wide, apex moderately emarginated with more robust hair-like setae (Fig. 7C). Ovipositor (Fig. 7A) 590 μm long; stylus narrow and almost straight, relatively short: ca 0.43× as long as distal portion of coxite. Coxite robust, short and wide, rounded at posterolateral angle; distal portion ca 1.16× as long as wide at middle, slightly bent, with numerous conspicuous stout peg-like setae and with a few thinner peg-like setae, the latter mainly at apical portion; inner margin densely pubescent; proximal portion about as long as distal portion, with several types of peg-like and short fine hair-like setae (omitted in Fig. 7A). Transverse baculum well sclerotized; longitudinal baculum of paraprocts (valvifers) almost twice as long as coxite (measured from the apical margin of coxite to point where it is joining the transverse baculum).

Females are on average larger and broader than males from the same population, with more elongate ventrite 5, and the longitudinal depression of their metaventrite is broader but shallower.

The specimens vary moderately in size (Table 4). In contrast to, e.g., Ancyronyx sarawacensis and A. procerus, the elytral color pattern varies only slightly (Fig. 3B). Only a single specimen possesses a bicolored head (Fig. 3E). The surface structure of the head varies moderately in the density of the tubercles and punctures, and most of the specimens lack any trace of the frontoclypeal suture. The shape of the elytra indicates that the specimens have reduced hind wings, in contrast to the apterous 32 specimens of A. variegatus examined by Shepard (2019).

At the type locality (Pa’ Ramudu River), the specimens were sampled from an approximately 200 m long stretch. The river was shallow, moderately meandering, about 7–15 m wide, slowly flowing through a degraded primary forest (data for 5 March 2019). Shallow reaches (10–40 cm) with slow current alternated with deeper pools (50–120 cm); the river was partly shaded by the riparian vegetation including large old trees, dense bamboo groves, shrubs and massive tree ferns (Cyathea sp.). The substrate contained gravel, sand, stones and exposed boulders; however, some shallow sections showed bedrock ledge only. Submerged wood, as well as large packs of bamboo roots were present mainly 50–100 m downstream of the connection with the Pa’ Masia River. Ancyronyx lianlabangorum sp. nov. was collected exclusively from massive, submerged logs in deeper pools with slow current. In contrast, submerged bamboo rootlets and smaller pieces of wood were inhabited only by Ancyronyx sarawacensis and A. acaroides.

The Pa’ Masia River represents a headwater stream in degraded primary forest (Fig. 5B). During our sampling on 6 March 2019, it was about 5–50 cm deep, 3–7 m wide and slowly flowing. Adults inhabited submerged wood in several deeper pools with almost no current.

A single female sampled on 28 June 2018 was found on a large submerged log in a pool of the entirely shaded, shallow Pa’ Kasi near the connection with Pa’ Kelapang River in the vicinity of Kampung Ramudu (Fig. 5C). The river bottom contained mainly firmly arranged pebbles and rocks.

Figure 5. 

Habitats of Ancyronyx lianlabangorum sp. nov. (A–C) and A. pulcherrimus (D) A type locality, Pa’ Ramudu River B Pa’ Masia River C Pa’ Kasi River D shaded shallow creek in primary forest, Gunung Mulu NP.

The altitude of the collection sites ranges from 900 to 970 m a.s.l.

Neither the intensive collection efforts in Pa’ Kelapang River near connections with Pa’ Ramudu, Pa’ Kasi, Pa’ Ngaruren and Pa’ Buah rivers near Kampung Ramudu revealed any further adults or larvae of A. lianlabangorum sp. nov., nor the samplings of the upstream sections of Pa’ Kelapang River near Batu Patong, Pa’ Mada as well as Pa’ Umor. However, in all these habitats we found submerged autochthonous wood inhabited by Ancyronyx sarawacensis, A. procerus, A. acaroides, and several species of Graphelmis, Leptelmis Sharp, Elmomorphus Sharp and Stenomystax Kodada, Jäch & Čiampor.

This species is known from a few small, slowly flowing tributaries of Pa’ Kelapang River near Kampung Ramudu, Kelabit Highlands, Sarawak.

We named the species in honor of David Lian Labang (“Uncle David”) and his son David Lian Labang Jr from Bareo (Kelabit Highlands, Sarawak). They run Labang Longhouse Lodge in Bareo. Ján Kodada and David Selnekovič have always been happy to take advantage of this fabulous accommodation during several field trips. Uncle David is a retired, well-known employee of the Forest Department Sarawak, who contributed to the knowledge and conservation of Sarawak’s nature. We are most grateful to both for many stories and shared information about the terrain, nature, culture, as well as for their endless repertoire of jokes!

Figure 6. 

Ancyronyx lianlabangorum sp. nov., aedeagus of holotype A ventral view B dorsal view C lateral view. Scale bar: 0.1 mm.

Figure 7. 

Ancyronyx lianlabangorum sp. nov. A ovipositor, paratype [JK145], ventral view B male sternite IX, holotype, ventral view C female sternite VIII, paratype [JK145], ventral view. Scale bars: 0.1 mm.

Ingei River, forest pool, , Belait District, Brunei.

Type material. Holotype ♂ (BM): “Brunei: Belait Distr. Sg. Ingei, forest pool near Base Camp, 14.VI.2010 leg. Mayyer Ling (34)”. Paratypes (NMW, UB): 1 ♂ and 2 ♀♀, same label data as holotype.

(CCB, CFDS, CKB, NMW, UBDM).

Lineage 1. Sarawak 9 ♂♂ [incl. JK100, JK213, JK214, JK215], 15 ♀♀ [incl. JK101, JK102, JK208, FZ1632]: “Malaysia, Sarawak, Marudi distr., Gunung Mulu NP, 16.10.2018, (40) 04.0267°N, 114.8234°E, 55 m a.s.l., small stream in primary forest, Kodada & Selnekovič lgt.”. Brunei 2 ♂♂, 1 ♀ [FR324]: “Brunei: Temburong; small Sungai Peradayan; rivulet, subm. wood; dist. primary forest; c. 25m a.s.l. c. 04.11.1997 leg. Mendoza (6f)”.

Lineages 2 and 3. Sarawak 5 ♂♂ [incl. JK105, JK106], 1 ♀ [JK12]: “Malaysia, Sarawak, Kuching distr., Bayur riv. near Kampung Bayur, 20.10.2018, 1°14'42.3"N, 110°17'35.3"E 40 m a.s.l., J. Kodada & D. Selnekovič lgt.”; 2 ♂♂ [JK197, JK199], 4 ♀♀ [incl. JK193, JK195]: same locality and collectors, but 22.02.2019, (No.43); 1 ♂ [FR344]: “Malaysia: Sarawak, Kg. Bayur 35km SSE Kuching, small hill river Bayur R.; run, subm. wood; second. veget./farmland; c. 50m a.s.l., c. 12.11.1993 leg. Mendoza (19f)”.

Ancyronyx pulcherrimus was represented by three barcode lineages, which are tentatively considered conspecific in the absence of further evidence. The specimens of the first lineage were collected in northern Sarawak and Brunei, while the specimens of the second and third lineages occur sympatrically in southwestern Sarawak. The first lineage is characterized by: (1) elytra predominantly black with a central yellowish, nearly X-shaped pattern and yellowish apices; (2) femora with black band between middle and proximal fourth; and (3) tibiae black on proximal three-quarters (compare Fig. 4 in Kodada et al. 2014). The type specimens are rather uniform in these characters, and all individuals recently collected in Gunung Mulu NP generally agree with them. However, there is some minor variation in the extent of the black coloration of the elytra, pronotum and legs (Fig. 4A, B). The examination of the hind wings of six specimens of the Gunung Mulu population and three specimens from Temburong (Brunei) revealed only short wings not reaching the abdominal apex (Fig. 4B). Macropterous or apterous forms were not detected, and the elytral shape of the remaining specimens suggests that they are flightless too.

The specimens of the second and third lineages differ from the type specimens in the predominantly yellowish elytra, which are provided with several black lateral and sutural spots of variable size. The pronotal spots are usually smaller, and the dark femoral bands are smaller, paler or obsolete (Fig. 4C, D). The examination of their hind wings revealed one macropterous and five brachypterous specimens.

Lineages detected by the analysis of COI nucleotide sequences were not confirmed by PCA analyses of morphometric characters (Fig. 2, Table 4) or corroborated by the genital morphology.

The stream inhabited by a large population of A. pulcherrimus was a small, slowly flowing, very shallow, and entirely shaded meandering creek in Gunung Mulu NP (55 m a.s.l.). It included large amounts of accumulated leaves, and the bottom substrate contained sand and gravel, as well as woody debris (Fig. 5D). The specimens co-occurred with Ancyronyx sarawacensis and two new species of Elmidae (Okalia Kodada & Čiampor and Leptelmis).

The second population was found in a moderately wide (5–8 m) lowland river near Kampung Bayur (Kuching Division); the sampled stretch was shallow and meandering, with sandy/gravelly substrate containing submerged logs, woody debris, and leaves. All specimens were collected exclusively in reaches with stronger current from submerged logs together with Ancyronyx procerus, A. acaroides, and several other Elmidae (Leptelmis sp. and Graphelmis spp. of the G. picta (Reitter) and G. marshalli Hinton species groups).

Ancyronyx pulcherrimus was so far known only from Brunei (Jäch et al. 2016). The species is here recorded for the first time from Malaysia, where it was collected in Gunung Mulu NP (northern Sarawak) and in the Kuching Division (southwestern Sarawak).

Our recent collecting activities found A. pulcherrimus to be less abundant and less widely distributed than A. sarawacensis, A. procerus, or A. acaroides, probably also due to the low dispersal ability of flightless populations.