Grouvellinus cruxniger Freitag, Molls and Bouma, 2019

Freitag, Hendrik, Molls, Christian, Bouma, Aglaia M., Garces, Jhoana M., Rossato, Marzia, Cosentino, Emanuela & Delledonne, Massimo, 2019, Additional new species of Grouvellinus Champion 1923 (Insectaı Coleopteraı Elmidae) discovered by citizen scientists and DNA barcoded in the field applying a novel MinIONbased workflow, Journal of Natural History 53 (41), pp. 2593-2620 : 2604-2608

Grouvellinus cruxniger Freitag, Molls and Bouma , sp. nov.

( Figures 5 , 12 (a,b), 13(a,c))

Type locality. Malaysia, Sabah (on Borneo Island), Tawau Hills Park, Tawau River, 4° 24 ʹ 14 ʹʹ N, 117°53 ʹ 35 ʹʹ E, 270 m a.s.l. ( Figure 1 (b,e)).

Type material. Holotype 3 [H1] (SP): ‘ MALAYSIA: Sabah: Tawau River; Light trap near Park Headquarters ; ca. 4°24 ʹ 14 ʹʹ N, 117°53 ʹ 35 ʹʹ E, 270 m a.s.l.; leg. Taxon Expedition participants 12. March .2018 (1)L ’, terminal parts of abdomen incl. aedeagus glued separately. Paratypes: 13, 2♀ (SP) ‘ MALAYSIA: Sabah: Tawau River; bottom gravel, run; primary forest; ca. 4°24 ʹ 14 ʹʹ N, 117°53 ʹ 35 ʹʹ E, 280 m a.s.l.; leg. Taxon Expedition participants 12. March.2018 (1c)M ’.

Etymology

The epithet refers to the elytral colour pattern which appears like a black cross especially in pale specimens with distinct yellowish markings.

Description

Body elongate obovate, 1.85 (males) – 1.90 (females) mm long (CL), 0.87 mm wide (EW), ca. 2.2 times as long as wide (CL/EW).

Dorsal colouration ( Figure 5 ) dominantly dark brown to black; pronotum black with gold-brown anterior margin; median transverse portion of elytra including disc dark brown to black; peripheral elytral portions with two pairs of more or less distinct, extended yellowish-brown spots; basal spots between shoulder and first row of punctures subquadrate; subapical spots between lateral margin and first row of punctures subtriangular; femora and tibiae dark brown; coxae, tarsi and antennae brown; maxillary and labial palps dark brown; pubescence shiny golden yellowish. Ventral side ( Figure 13 (b)) pale brown.

Head ( Figure 12 (a)) 0.37 – 0.39 mm wide (HW); ID 0.17 – 0.20 mm; frons and clypeus moderately densely pubescent; apical and lateral margins of labrum densely pubescent; punctures small; intervals medially flat and glabrous. Frontoclypeal suture straight, distinct. Eyes moderately large (eye diameter smaller than ID), slightly protruding. Antennae genus-typical.

Pronotum ( Figure 12 (a)) ca. 0.54 mm long (PL), ca. 0.67 mm wide (PW), wider than long (PL/PW), widest posterior 0.35, narrower than elytra, anteriorly distinctly attenuate; lateral margins evenly, strongly convex, anterior margin slightly convex, anterior angles sharp, almost rectangular; pronotal disc slightly vaulted; pronotum moderately densely punctate, slightly denser at disc; punctures very small and shallowly impressed; setae moderately long; median carina absent, with indistinct pair of small posterior-median rugose patches (anterior of the scutellum); sublateral carinae indistinct and short; laterobasal and oblique impressions (the latter extending ca. posterior 0.35 – 0.60) very shallow; disc, entire anterior portion and portion between sublateral carinae and posterior-median patches glabrous; laterobasal angles and impressions rugose. Hypomeron very densely punctate.

Prosternum ( Figure 12 (b)) moderately long; lateral portions appearing rugulose, with plastron-like sense pubescence; anterior median portion clearly divided by tilt from the process, slightly rugulose to almost glabrous; prosternal process subtrapezoidal, approximately as long as wide at the base, medially spaciously impressed, rugulose, posterior margin convex, angles gently rounded.

Scutellum subcordiform, flat, with few minute punctures. Elytra ( Figure 5 ) elongate, subparallel anterior 0.1 – 0.4, moderately convex dorsally, 1.34 (males) – 1.41 (females) mm long (EL), ca. 1.6 times as long as wide (EL/EW), widest at anterior 0.6; apices broadly and almost conjointly rounded; with eight longitudinal, slightly impressed rows of primary punctures (striae); primary punctures moderately large and moderately deeply impressed, increasingly smaller and more shallowly impressed apicad, regularly arranged in median rows, less regularly arranged in lateral rows; interstices glabrous; intervals with additional, very small setiferous secondary punctures; pubescence yellowish, regularly arranged along intervals, consisting of sparse, large erected setae (frequently broken), and moderately large more or less adpressed setae; interval 8 with (genus-typical) serrate carina, interval 2 not carinate; lateral elytral margin inconspicuously serrate.

Mesoventrite ( Figure 12 (b)) with two pairs of deep grooves, one behind procoxae, another medially; the latter widely trapezoidal in males, subquadrate in females. Metaventrite ( Figure 12 (b)) with large, predominantly glabrous disc (interrupted by scattered setiferous tubercles); longitudinal impression along median suture shallow and limited to posterior two-thirds in females, over full length and deeper in males; portions adjacent to disc and coxae with irregular, deep impressions, punctures and tubercles, with distinct patch of long, yellowish setae next to mesocoxae (in both sexes); most lateral portions densely punctate and with pubescence (plastron).

Ventrite 1 ( Figure 12 (b)) with pair of longitudinal carinae between almost glabrous disc lateral portions; extended lateral portions of ventrites 1 – 2 and almost entire ventrites 3 – 5 ( Figure 12 (b)) densely covered with plastron and scattered, moderately long setae; glabrous median portion extended only up to ventrite 2; ventrite 5 with fringe of moderately long setae at lateroapical margin.

Legs ( Figure 5 ) slightly longer than body and all approximately of the same length; tibiae longer than tarsi and femora; inner (more conspicuously) and outer ventral margin of all tibiae with longitudinal patch of long trichoid setae (in both sexes); faces of femora and tibiae densely covered with short adpressed setae (plastron-like at inner femora) and some longitudinally arrange long trichoid or spine-like setae. Legs not conspicuously varying between sexes.

Aedeagus ( Figure 13 (a,b)) ca. 615 μm long, ca. 180 μm wide. Phallobase slightly asymmetrical basally, reaching basal 0.5 of total aedeagus length. Median lobe ca. two times as long as wide, distinctly overreaching parameres and ventral sac, evenly conical towards the broadly round apex, apically slightly bent ventrad (lateral view). Ventral sac internally very densely covered with comparably long, thin spines that do not reach the apical opening. Parameres conical (in lateral view) almost subparallel in ventral view, apices asymmetrically rounded; with slightly more than 30 trichoid setae in apical half, most of them at the ventrolateral margin; most apical two setae longest.

Ovipositor ( Figure 13 (c)) total length ca. 730 μm; stylus ca. 36 μm long, very sligthly bent outwards with three short sensilla; coxite ca. 340 μm long with scattered extremely short, acute setae, apically slightly broadened at outer margin, with four broad hook-like setae; distal portion medially very slender, ca. 2.7 times as long as proximal portion; valvifer 390 μm long, caudal portion slightly sclerotised and with scattered, extremely short, acute setae; fibula almost straight.

Differential diagnosis

Grouvellinus cruxniger sp. nov. is similar to G. andrekuipersi and G. nigerquadratus sp. nov. especially in the yellowish elytral patterns commonly observed in pale specimens, but the borders of these patterns towards the elytral disc are more or less straight so that the remaining black elytral portions appear cross-like, with a broad transverse cross band and a slenderer sagittal band. G. cruxniger sp. nov. can be distinguished from the latter by the slightly larger size (CL 1.85 – 1.90 mm, vs. 1.7 – 1.8 mm and 1.50 – 1.75 mm, respectively), the pronotum with strongly convex lateral margins, the rectangular, acute anterior angles (vs. protruding acute, or obtuse anterior angles) and the almost conjointly rounded elytral apices. From all known Bornean Grouvellinus spp. it varies in the presence of distinct patches of long, yellowish setae at the anteriolateral metaventrite and its comparably simple aedeagus with unique combination of long phallobase (reaching ca. basal 0.5 of total aedeagus length), median lobe evenly conical and apically gently rounded, parameres conical (in lateral view) with asymmetrically rounded apices and slightly more than 30 trichoid setae in apical half.

The species varies at least by 6.3% genetic distance (654 bp CO1 barcode) from the most similar Bornean congener G. nigerquadratus sp. nov.

Distribution

This species is only known from the type locality at the Tawau Hills Park, Sabah, Borneo Island ( Figure 18 ).

Figures

Figure 1. (a) Co-authors and assistants of the Taxon Expedition to Tawau Hills Park, Sabah, Malaysian Borneo, performing microhabitat-specific sampling; (b) Co-authors during beetle collection at a blacklight trap installed in the vicinity of the Tawau River; (c) The first author (second from the right) instructing Taxon Expedition participants on the identification of riffle beetles; (d) the transportable molecular field laboratory at the Tawau Park Station; (e) Type locality of Grouvellinus borneensis, sp. nov., G. cruxniger, sp. nov., G. nigerquadratus, sp. nov., and collection site of G. sp. 1; (f) Type locality of Grouvellinus luciaensis, sp. nov., and collection site of G. andrekuipersi, G. nigerquadratus, sp. nov. and G. sp. 2.

Figure 12. Grouvellinus cruxniger, sp. nov. (paratypes): (a) anteriodorsal aspect with pronotum and elytra; (b) ventral aspect with prosternum, meso-, metaventrite, and ventrites 1–5.

Figure 13. Grouvellinus cruxniger, sp. nov. (paratypes): (a) aedeagus, lateral; (b) aedeagus, ventral; (c) ovipositor (half), ventral. Scale bar = 0.1 mm.

Figure 18. Map of Sabah and Brunei (Borneo) with collecting site of Grouvellinus species with new species record in red fonts.

Figures 2–5. Habitus of the Grouvellinus species collected from the Tawan Hills Park. 2: G. andrekuipersi; 3: G. nigerquadratus, sp. nov. (paratype male from Tawau River); 4: G. nigerquadratus, sp. nov. (male from Lucia River); 5: G.cruxniger, sp. nov. (paratype male from Lucia River). Scale: 1 mm.