Ancyronyx clisteri, Kodada & Jäch & Freitag & Čiamporová-Zaťovičová & Goffová & Selnekovič & Jr, 2020

Kodada, Jan, Jaech, Manfred A., Freitag, Hendrik, Ciamporova-Zatovicova, Zuzana, Goffova, Katarina, Selnekovic, David & Jr, Fedor Ciampor, 2020, Ancyronyx clisteri, a new spider riffle beetle species from Borneo, redescription of A. sarawacensis Jaech including a description of the larva and new distribution data for A. procerus Jaech using DNA barcodes (Coleoptera, Elmidae), ZooKeys 912, pp. 25-64 : 25

Ancyronyx clisteri sp. nov.

Type locality

(Fig. 11A ). River, about 10 m wide (tributary of Kuamut River near Kampung Pisang Pisang), meandering, with submerged wood; Sabah, Malaysia.

Type material.

Holotype ♂ (NMW): "Malaysia, Sabah, Kuamut river env. near Kampung Pisang Pisang, 3.-4. VII. 1996, 14b: ca 10 m wide tributary of Kuamut River in primary forest". Paratypes (BOR/COL, CCB, CFDS, CFM, CKB, NMW, RMNH, UBDM): 1 ♂, 2 ♀♀: same locality data as holotype; 5 ♂♂, 8 ♀♀: "Malaysia, Sabah, (Borneo), Kuamut river env. near Kampung Pisang Pisang, 3.-4. VI. 1996, 14a: shaded stream in primary forest with submerged wood"; 2 ♀♀: "Malaysia, Sabah, Kampung Pisang Pisang env., tributary of Kuamut River, 29. VI. 1998"; 4 ♂♂, 7 ♀♀: "Malaysia, Sabah, Sabalangang river in primary forest ca 25 km SE Sapulut, 26.06.1998"; 1 ♀: "Malaysia, Sabah, ca 5 km S Sapulut, Saliku river,16.V.2001"; 1 ♀: "Malaysia: Sabah: Maliau Basin Studies Center: Kuamut River tributary, road bridge near observation tower; submerged wood, riffle; 4°42'48"N, 116°58'34"E, 280 m asl.; 03.Oct2017, leg. H. Freitag & C.V. Pangantihon / Taxon Expeditions (KRC1f)"; 1 ♀ [FZ1640, MK505421]: "Malaysia, Sarawak, Marudi distr., Gunung Mulu NP, 17.10.2018, (42) 04.0267N, 114.818083E, 60 m a.s.l., river, J. Kodada & D. Selnekovič lgt."; 5 ♂♂ [H44, LR735552], 7 ♀♀: "Brunei: Temburong, Belalong River tributary Sungai Sibut; W of Ashton Trail, submerged wood, run; 4°32'38"N, 115°08'51"E, 170 m asl.; leg. Pangantihon / Taxonexpeditions 29.Sep2018 (SiCf)M".

Diagnosis.

Ancyronyx clisteri sp. nov. is a medium sized, elongate species with dark head and elytra (Fig. 3A, B ). It is morphologically most similar to Ancyronyx sarawacensis from which it can be distinguished by: 1) elytra extensively black with a very narrow yellowish band along anterior margin and a moderately wider yellowish portion dividing anterior and posterior black area; 2) ovipositor with longer and narrower distal portion of coxite (2.7-2.9 × as long as wide near middle); 3) proximal portion of coxite ca 0.7-0.8 × as long as distal portion; 4) longitudinal baculum of paraprocts ca 1.04-1.19 × as long as entire coxite length; 5) about 9% divergence of the partial mtDNA for cytochrome c oxidase subunit COI (COI barcodes with 90.7% similarity between A. clisteri sp. nov. and A. sarawacensis , based upon 661 base pairs). We were unable to find significant differences between the aedeagi of these two species, although in direct comparison the apex of the penis of A. clisteri sp. nov. usually appears to be narrower and more pointed than that of A. sarawacensis . Some A. sarawacensis from Sabah (e.g., Figs 3D , 4A ) show darker heads and pronota and wide anterior and posterior elytral spots, their color pattern is very similar to those of A. clisteri sp. nov. (see respective comment on variability below). For their correct identification it is best to use the COI barcodes or comparison of ovipositors. It is possible that some of the dark males of A. sarawacensis cannot be identified by morphological features without direct comparison with A. clisteri sp. nov.

Description of holotype.

Body form moderately elongate, elytra moderately convex dorsally, with highest point near midlength; BL: 1.64 mm, EW: 0.74 mm, BL/EW: 2.22.

Coloration (Fig. 3A, B ). Labrum yellowish-brown; mouth parts and antennae yellowish, clypeus and narrow anterior portion of frons yellowish, remaining portions of cranium black dorsally and posteriad of eyes; pronotum yellowish with large mesal black spot; spot distinctly narrowed near middle; scutellum brownish; elytra mostly black, with yellowish anterior margin and two oblique yellowish stripes meeting at suture; elytral apices yellowish. Venter yellowish except for almost black mesanepisterna, metanepisterna, lateral portion of metaventrite and lateral portions of ventrite 1; coxae yellow; femora black on distal one sixth, yellowish on remaining portion; tibiae black on proximal three fourths and near articulation with tarsi, yellowish on distal fourth; tarsomeres 1-2 darker, tarsomeres 3-5 and claws yellowish.

Head. Labrum about as long as clypeus, with anterior margin slightly concave, almost straight; surface with dual punctation; larger punctures deeper with fine setae, smaller punctures very fine and shallow. Clypeus wide, densely punctate and finely reticulate. Frons and vertex densely, finely punctate, appearing reticulated; reticulation more distinct on black portion of vertex; surface with narrow, elongate, hardly discernible granules (Fig. 5C ); frontoclypeal suture almost straight, finely impressed. Eyes moderately protruding and large. Antennae 11-segmented, subequal in length with pronotum; each antennomere with a few scattered trichoid setae (sensilla trichoidea); antennomeres 9-11 each with two clusters of peg-like setae near distal margins (Fig. 5D, E ); terminal segment with additional different sensilla. Ratio of length of antennomeres 1-11: 0.049: 0.053: 0.039: 0.028: 0.031: 0.028: 0.037: 0.033: 0.041: 0.045: 0.093 mm. Gena microsculptured; gula narrow, smooth; gular sutures absent; posterior tentorial pits deep and large. HW: 0.39 mm; ID: 0.22 mm.

Thorax. Pronotum distinctly wider than long (PL/MW: 0.84), widest near posterior angles; anteriorly attenuate; anterior margin strongly arcuate; almost entire hypomeral portion visible in dorsal view; anterior transverse groove distinctly impressed, oblique and dividing pronotum; area posteriad of transverse groove strongly gibbous; anterior mesal longitudinal carina absent; posterolateral oblique grooves moderately impressed. Pronotal surface densely punctate and irregularly reticulate on disc; anterior and posterior portion smooth (Fig. 5A, F ); flat cordiform granules mainly laterally and anteriorly; PL: 0.48 mm, MW: 0.57 mm. Prosternum irregularly, densely and roughly punctate, very short in front of procoxae; prosternal process distinctly transverse, almost flat; posterior margin widely rounded, feebly protruding posteriad; lateral margins arcuate. Scutellum subpentagonal, smooth and shiny. Elytra elongate; EL: 1.18 mm; slightly narrowed at the level of metacoxae, then gradually convergent towards conjointly rounded apices; with ten more or less regular rows of punctures; six rows between suture and shoulder; accessory scutellary rows absent (Fig. 6A ); punctures large, round and deeply impressed on disc and laterally (Fig. 6A, B ), smaller and less distinct anteriorly and posteriorly; interstices and intervals wider and flat on disc, narrower and feebly convex laterally and posteriorly; surface very finely sculptured; humeri prominent. Mesoventrite almost flat, approximately half as long as prosternum length; mesoventral cavity shallow and narrow; surface strongly and irregularly punctate; mesoventral discrimen invisible; posterior angles rounded and moderately protruding. Metaventrite along midline distinctly longer than combined length of prosternum and mesoventrite; anterior margin arcuate; disc with shallow longitudinal depression mesally; discrimen strongly depressed (Fig. 5B ); surface of disc glabrous with fine scarce punctures; distinct, deep irregular punctures along anterior margin and on lateral portions of metaventrite; punctures coarser and denser laterally. Hind wings fully developed. Forelegs about 1.47 × as long as body length; pro- and mesocoxae large and prominent, strongly protruding laterad, bluntly drop-shaped; metacoxae smaller and less protruding laterad; femora, tibiae, and tarsi with short setae; tibiae with a few additional longer setae; distal tarsal segments with several longer setae near apex; claws large, strongly curved, base with two small teeth.

Abdomen. Abdominal intercoxal process moderately longer than length of ventrite 1 posterior of metacoxae, very wide, anteriorly widely arcuate, with rows of deep large punctures along anterior margin; ventrite 1 longest; ventrite 2 ca 0.75 × as long as ventrite 1; ventrite 3 ca 0.88 × as long as ventrite 2; ventrite 4 ca 0.75 × as long as ventrite 3; ventrite 5 as long as combined lengths of ventrites 3 and 4. Surface of ventrites 2-5 with sparse punctures and setigerous flat, more or less cordiform granules; punctures more distinct on mesal portion; granules more prominent and more conspicuous laterally; ventrite 5 granulate. Male sternite IX ca 340 μm long; apical margin arcuately, but distinctly emarginated; lateroapical portion with a few moderately long setae; paraprocts not reaching beyond apical margin. Tergite VIII finely reticulate, with conspicuous median transverse ridge separating posterior and anterior portion; basal half with microtrichial pattern; apical margin hyaline, with subapical fringe of hair-like setae; setae on sublateral portions stronger and longer than those along margin.

Aedeagus (Fig. 13A, B ) ca 350 μm long; penis (including lateral basal apophyses) ca 2.85 × as long as phallobase, gradually tapering apicad; apical half moderately curved ventrad (LV), dorsolateral portion with only a few very short setae; apex narrowly rounded; lateral basal apophyses long; ventral sac large; fibula conspicuous, moderately wide; surface of endophallus with spinules; corona indistinct. Phallobase asymmetrical; parameres moderately exceeding middle of penis, widest near base, narrowed to apex; dorsal margin arcuate; ventral margin feebly sinuate; apex narrowed and rounded; mesal and outer surface of parameres with short setae.

Description of ovipositor

(Fig. 14A-C ). Ovipositor ca 490 μm long; stylus narrow and long, almost straight, ca 0.50 × as long as coxite (compared to the length of distal portion of coxite). Coxite moderately long and stout, rounded at posterolateral angle; distal portion ca 2.70-2.90 × as long as wide near middle, slightly bent, with numerous short stout peg-like setae and with a few thinner peg-like setae; latter mainly at apical portion; inner margin moderately pubescent; proximal portion ca 0.70-0.80 × as long as distal portion, with peg-like and short, fine hair-like setae. Transverse baculum well sclerotised; longitudinal baculum of paraprocts (valvifers) ca 1.04-1.19 × as long as coxite (measured from apical margin of coxite to point where it is joining the transverse baculum).

Secondary sexual dimorphism.

Not strongly pronounced. Females on average longer and wider than respective males, with longitudinal depression of metaventrite narrower and shallower. Ventrite 5 in females longer and narrower than in males.

Variability.

The specimens vary moderately in size (Tabs 4 , 5 ). The elytral coloration exhibits, in contrast to Ancyronyx sarawacensis , only minor variation: some specimens have a larger yellowish anterior margin, oblique yellowish stripes and yellowish apices. In the genitalia, we detected only minor variability in the form of the penis. However, the dataset is too limited for a well supported statistical analysis.

Habitat.

The type locality is a shallow meandering river of about 10 m width flowing through primary forest, with stony substrate and plenty of submerged wood (Fig. 11A ). Specimens were collected exclusively from submerged wood predominatly in stream reaches with relatively strong current. The specimens from Brunei were collected in a very similar habitat - an upland headwater stream in (slightly disturbed) primary forest (Fig. 12A ); the small piece of submerged wood from which the specimens were collected was found in a very shallow, slowly flowing reach (Fig. 12A ). A single female was collected from submerged wood in fast flowing, shallow water in a small tributary in primary rainforest (280 m a.s.l.) near the Maliau Basin, Sabah. The altitude of all collection sites ranges from 60-300 m a.s.l. The limited number of collection sites suggests that this species is restricted to rather pristine forest streams at lower altitudes.

Syntopic taxa.

At the type locality specimens were collected together with Ancyronyx acaroides , A. procerus and A. sarawacensis , all found on the same submerged tree trunk. Some species of Graphelmis Delève ( Elmidae ), Elmomorphus Sharp and Stenomystax Kodada, Jäch & Čiampor ( Dryopidae ) also occurred in the same microhabitat. However, in Temburong, besides Ancyronyx acaroides , and A. sarawacensis , no other species were collected from exactly the same piece of submerged wood.

Distribution.

This species is presently known from a few localities in northern Borneo: Brunei, Sabah and Sarawak.

Etymology.

The species is named after Clister V. Pangantihon of the Ateneo de Manila University (Philippines), assistant at Taxon Expeditions, who discovered the new species during the expedition to Brunei. The name was selected by Taxon Expedition participants, instructors and staff of the Kuala Belalong Field Studies Centre in recognition for Clister’s discovery and his most appreciated engagement and friendly care for the expedition participants.

Figures

Figure 3. Habitus of: A Ancyronyx clisteri sp. nov., holotype B A. clisteri sp. nov., female paratype from Gunung Mulu NP, Sarawak C A. sarawacensis, holotype D A. sarawacensis, male from a tributary of Kuamut River " (14 a) ", Sabah.

Figure 4. Habitus of: A Ancyronyx sarawacensis, male from the tributary of Kuamut River " (14 a) ", Sabah B A. sarawacensis, male paratype from Kapit area, Sarawak C A. sarawacensis, female paratype from Gunung Mulu NP, Sarawak D A. sarawacensis, female from Bayur River near Kampung Bayur, Sarawak.

Figure 5. Ancyronyx clisteri sp. nov., SEM micrographs, male paratype from the type locality: A habitus, dorsal view B same specimen, ventral view C head, reticulate surface and granules, dorsal view D head, detail of mouth parts and antenna, ventral view E antennal apex with clusters of sensilla, ventrolateral view F pronotum with reticulate surface structure, dorsal view.

Figure 6. SEM micrographs: A, B Ancyronyx clisteri sp. nov. (male paratype from the type locality) C-F A. sarawacensis (female from the type locality). A Elytra and scutellum, anterior portion, dorsal view B same, detail of elytral surface, dorsal view C habitus, dorsal view D same, ventral view E head, pronotum and anterior portion of elytra, dorsal view F pronotum with reticulate surface structure, dorsal view.

Figure 11. Habitats of Ancyronyx clisteri sp. nov. and A. sarawacensis: A type locality of A. clisteri sp. nov., tributary of the Kuamut River near Kampung Pisang Pisang, Sabah B atypical locality of A. sarawacensis, shaded shallow stream in primary forest, Gunung Mulu NP, Sarawak C type locality of A. sarawacensis, small stream above Arur Dalan near Bario, Kelabit Highlands, Sarawak.

Figure 12. Habitats of Ancyronyx clisteri sp. nov. (A) and A. sarawacensis (B, C) sampled during Taxon Expeditions: A Sibut Creek (tributary of Belalong River), Temburong, Brunei, microhabitat (piece of submerged wood from which A. clisteri sp. nov. was collected) B Belalong River near Kuala Belalong Field Studies Centre, Temburong C Agatis River in the vicinity of Maliau Basin, Sabah, Malaysia. All photographs by Clister V. Pangantihon.

Figure 13. A Ancyronyx clisteri sp. nov., aedeagus of holotype with endophallus partly extruded, ventral view B same, lateral view C A. sarawacensis, larval mandible, ventral view.

Figure 14. Ancyronyx clisteri sp. nov.: A ovipositor, paratype from Sarawak, dorsal view B same, ventral view C ovipositor, paratype from the type locality, ventral view.