Grouvellinus luciaensis Freitag, Molls and Bouma, 2019Grouvellinus borneensis 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 : 2608-2616

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

( Figures 6 , 14 (a – d), 15(a – c))

Type locality. Malaysia, Sabah (on Borneo Island), Tawau Hills Park, Lucia River, 4° 28 ʹ 34 ʹʹ N, 117°55 ʹ 38 ʹʹ E, 750 m a.s.l. ( Figure 1 (f)).

Type material. Holotype 3 (SP): ‘ MALAYSIA: Sabah: Lucia River; rock surface, run; primary forest; ca. 4°28 ʹ 34 ʹʹ N, 117°55 ʹ 38 ʹʹ E, ca. 750 m a.s.l., leg. Taxon Expedition participants 10. March .2018 (6g)M ’, terminal parts of abdomen incl. aedeagus glued separately . Paratypes: 3♀ (SP) same data as holotype; 13 [H12], 2♀ (SP) ‘ MALAYSIA: Sabah: Lucia River; submerged wood, run; primary forest; ca. 4°28 ʹ 34 ʹʹ N, 117°55 ʹ 38 ʹʹ E, ca. 750 m a.s.l., leg. Taxon Expedition participants 10. March .2018 (6f)M ’ ; 3 1♀ [H22] (SP) ‘ MALAYSIA: Sabah: Lucia River; submerged root packs, run; primary forest; ca. 4°28 ʹ 34 ʹʹ N, 117° 55 ʹ 38 ʹʹ E, ca. 750 m a.s.l., leg. Taxon Expedition participants 10. March .2018 (6h)M ’.

Etymology

The species is named in reference to its type locality, Mt. Lucia and Lucia River originating there.

Description

Body elongate obovate, males 1.91 – 1.96 mm, females 1.97 – 2.04 mm long (CL); males 0.89 – 0.91 mm, females ca. 0.96 mm wide (EW), ca. 2.1 times as long as wide (CL/EW).

Dorsal colouration ( Figure 6 ) almost entirely dark brown to black; legs paler, at least distal half of femora and claws golden brown; maxillary and labial palps dark golden brown; pubescence shiny yellowish, rather inconspicuous. Ventral side ( Figure 14 (b – d)) dark brown.

Head ( Figure 14 (a)) 0.39 – 0.43 mm wide (HW); ID 0.19 – 0.24 mm; disc of frons, clypeus, and anterior and lateral areas of labrum sparsely pubescent; clypeus with two pairs of conspicuous sublateroanterior setae and entire frontal and lateral margins of labrum densely pubescent; punctures small; intervals glabrous; except for rugulouse frontal portion bordering eyes. Frontoclypeal suture straight, distinct. Eyes moderately large (eye diameter smaller than ID), slightly protruding. Antennae genus-typical.

Pronotum ( Figure 14 (a)) in males: 0.52 – 0.54 mm, in females: 0.53 – 0.57 mm long (PL); in males: 0.65 – 0.67 mm, in females: 0.66 – 0.72 mm wide (PW), wider than long (PL/PW), widest posterior 0 – 0.3, distinctly narrower than elytra, anteriorly attenuate; anterior margin slightly convex; pronotal disc moderately vaulted; entire pronotum moderately sparsely punctate; punctures small and shallowly impressed; median carina absent; with a pair of small and moderately deep posterior-median pits (anterior of the scutellum); sublateral carinae distinct and short; oblique impression moderately deep, narrow and glabrous, extending approx. anterior 0.35 – 0.65; laterobasal impression shallow, rugose; setae moderately short; interstices glabrous and flat. Hypomeron densely punctate, punctures large. Prosternum ( Figure 14 (b)) short; lateral portions with pubescence (plastron); median portion including process medially broadly impressed, slightly rugulose; prosternal process trapezoidal, slightly longer than wide, medially impressed.

Scutellum ( Figure 14 (a)) subtriangular, flat, glabrous. Elytra ( Figure 6 ) elongate, subparallel anterior 0.15 – 0.60, moderately convex dorsally, in males: 1.41 – 1.44 mm, in females: 1.44 – 1.48 mm long (EL), 1.5 – 1.6 times as long as wide (EL/EW), widest in anterior half; apices narrow, distinctly separately rounded; with eight longitudinal, distinctly impressed rows of punctures (striae); stria 8 reaching only up to 0.4 posterior; punctures somewhat regularly arranged, distinctly larger (diameter larger than interstices) and very deeply impressed in anterior and lateral portions, increasingly shallower and smaller apicad; interstices glabrous to finely rugulouse; median elytral portion, especially along interval 1 with additional very small setiferous secondary punctures; pubescence inconspicuous, consisting of very small adpressed setae and moderately large erected setae; interval 8 evenly carinate, but not serrate; interval 7 very slightly carinate; interval 5 (and intervals 2 – 4 in lesser extent) broadly elevated in subanterior portion; lateral elytral margin carinate with fine serration.

Mesoventrite ( Figure 14 (c)) with two pairs of shallow grooves behind procoxae and medially, respectively. Metaventrite ( Figure 14 (d)) moderately densely punctate, less densely at disc; longitudinal impression along entire median suture; lateral portions rather flat with inconspicuous plastron and a row of large punctures behind mesocoxae.

Ventrite 1 ( Figure 14 (d)) with pair of longitudinal carinae bordering disc; disc glabrous, sparsely punctate; lateral portions inconspicously pubescent (plastron); broad lateral portions of ventrites 1 – 4 and almost entire ventrite 5 ( Figure 14 (d)) densely covered with rather inconspicuous micro-plastron; ventrite 5 densely covered with setiferous tubercles and with apical fringe of moderately long setae.

Legs ( Figure 6 ) approximately as long as body; hindleg longest; tibia longer than tarsus and femur in all legs; proximal portion of mesofemur with loose fringe of moderately long trichoid setae at anterior-dorsal ridge (in both sexes); distal area of all tibiae with more or less densely covered with short trichoid setae; hind tibia additionally with loose longitudinal fringe of robust spine-like setae; coxae, trochanter, and particularly inner and posterior faces of femora and tibiae covered with conspicuous plastron setae. Legs not conspicuously varying between sexes.

Aedeagus ( Figure 15 (a,b)) ca. 635 μm long, ca. 190 μm wide. Base reaching basal 0.38 of total aedeagus length. Median lobe ca. four times as long as wide, moderately overreaching parameres, abruptly tapering in apical third towards the slender conical, rounded apex. Ventral sac apically inflated overreaching median lobe and parameres, internally densely stippled and with dense submedian fringes of moderately long, thin spines; apically the spines get longer and reach the apical opening. Parameres apically moderately conical (in both, ventral and lateral view), usually with more than 50 trichoid setae in apical two-third, most of them at the outer ventral face; most apical two setae longest and inserted at the apex. Male sternite IX as in previous new species.

Ovipositor ( Figure 15 (c)) total length ca. 790 μm; stylus ca. 40 μm long, moderately bent outwards with three short sensilla; coxite ca. 375 μm long with scattered extremely short, acute setae and four hook-like bent sensilla, apically moderately broadened at outer margin, valvifer ca. 430 μm long, caudal portion slightly sclerotised and with very few scattered, extremely short, acute setae; fibula almost straight.

Sexual dimorphism

Females with separately rounded and slightly more pointed elytral apices.

Differential diagnosis

Grouvellinus luciaensis sp. nov. can be distinguished from all known Bornean Grouvellinus spp. by its moderately large size (CL) of 1.91 – 2.04 mm (vs. ≤ 1.9 mm, or ≥ 2.3 mm), somewhat straight conical elytral posterior portion, very deeply impressed elytral striae in anterior and lateral portions, and a non-serrate 8th elytral interval. Furthermore, it is recognisable by the slight and uniform reddish-brownish tinge of the body, comparably pale femora, the aedeagal median lobe that is abruptly tapering in apical third and the comparably broad parameres with more than 50 trichoid setae in apical two-third.

The species varies by about 11 – 17% genetic distance (654 bp CO1 barcode) from the Bornean congeners.

Distribution

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

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

( Figures 7 , 16 (a – c), 17(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 (a,e)).

Type material. Holotype 3 [H7] (SP): ‘ MALAYSIA: Sabah: Tawau River; Light trap near Park Headquarter ; 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: 9 3, 4♀ (SP) same data as holotype; 13, 1♀ [H49] (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 species is named for the island of Borneo, where it is most likely endemic.

Description

Body elongate obovate, males 1.50 – 1.56 mm, females 1.60 – 1.67 mm long (CL), males 0.74 – 0.78 mm, females 0.80 – 0.83 mm wide (EW), 2.0 times as long as wide (CL/EW).

Dorsal colouration ( Figure 7 ) almost entirely dark brown to black, only tarsi, antennae and maxillary palps golden brown; pubescence pale brown. Ventral side ( Figure 16 (b,c)) brown to pale brown.

Head ( Figure 16 (a,b)) in males 0.33 – 0.35 mm, in females 0.37 – 0.39 mm wide (HW); ID 0.14 – 0.17 mm; frons, clypeus, and labrum sparsely pubescent, slightly denser in lateral portions; punctures very small and scattered; intervals flat, glabrous. Frontoclypeal suture almost straight. Eyes large (eye diameter larger than ID), very slightly protruding. Antennae genus-typical.

Pronotum ( Figure 16 (a)) in males 0.44 – 0.45 mm, in females 0.46 – 0.50 mm long (PL), in males 0.52 – 0.56 mm, in females 0.59 – 0.63 mm wide (PW), wider than long (PL/PW), widest basally, narrower than elytra, anteriorly attenuate; anterior margin moderately convex; pronotal disc slightly vaulted; entire pronotum moderately densely punctate; punctures small and shallowly impressed; setae moderately short; median carina absent; pair of posteriormedian rugose patches distinct; sublateral carinae indistinct and short; laterobasal impression shallow, rugulose; oblique impressions shallow, partly rugulose, extending obliquely from anterior 0.2 – 0.6, then continuing aside sublateral carinae up to posterior margin; entire anterior portion and portion between sublateral carinae and posterior-median patches glabrous; disc anterior of these patches slightly rugose. Hypomeron very densely punctate.

Prosternum ( Figure 16 (c)) short; lateral portions with inconspicuous plastron pubescence; median portion including process very shallowly impressed, slightly rugulose; prosternal process subquadrate.

Scutellum ( Figure 16 (a)) subcordiform, flat, rugose, with few setiferous punctures. Elytra ( Figure 7 ) elongate, moderately convex dorsally, in males 1.07 – 1.10 mm, in females 1.22 – 1.24 mm long (EL), in males ca. 1.4 times, in females ca. 1.3 times as long as wide (EL/ EW), conspicuously widest at anterior 0.6, slightly attenuating anteriad, roundly attenuating posteriad; apices wide, almost conjointly rounded; with eight longitudinal, slightly impressed rows of primary punctures (striae); primary punctures large and moderately deeply impressed at median disc, slightly smaller in basal portion and increasingly smaller and more shallowly impressed apicad, regularly arranged in median rows, less regularly arranged in lateral rows; interstices and interval rugose; interval 8 with (genus-typical) serrate carina; interval 2 slightly carinate; all intervals with setiferous secondary punctures (inconspicuous due to rugose surface); pubescence yellowish, consisting of moderately large, erected setae and small adpressed setae; lateral elytral margin more or less distinctly serrate.

Mesoventrite ( Figure 16 (c)) with 2 pairs of subtrapezoidal grooves, median pair shallowly impressed, lateral pair (behind procoxae) deeply impressed. Metaventrite ( Figure 16 (d)) with distinct median suture over the entire length. Median disc glabrous, slightly dimorphic between sexes; lateral and marginal portions moderately densely covered with setiferous tubercles and inconspicuous plastron.

Ventrite 1 ( Figure 16 (d)) comparably short; carinae bordering glabrous disc oblique and rather inconspicuous; ventrites 1 – 2 only glabrous in most anteriomedian portion; lateral portions of ventrites 1 – 2 and entire ventrites 4 – 5 moderately densely covered with setiferous tubercles and inconspicuous plastron; apical margin of ventrite 5 fringed with pubescence.

Legs ( Figure 7 ) approximately of the same length as body; tibiae longer than tarsi and femora; trochanter, femura and tibiae almost entirely densely covered with setiferous tubercles and plastron setae except almost glabrous outer, dorsal face of tibiae and inner face of tibiae and femora. Mesofemur with loose fringe of short trichoid setae on the anterior – dorsal ridge. Legs not conspicuously varying between sexes.

Aedeagus ( Figure 17 (a,b)) ca. 510 μm long, ca. 115 μm wide. Phallobase slightly asymmetrical basally, reaching ca. basal 0.31 of total aedeagus length. Median lobe moderately wide (ventral view), moderately overreaching parameres and ventral sac, very slightly conical in apical half, then abruptly tapered at the level of paramere tips towards slender apex; apex slightly bent ventrad (lateral view). Ventral sac internally densely stippled and with dense fringe of moderately short, thin and comparably delicate spines; few of those overreaching apical fringe. Parameres moderately shorter than median lobe and distinctly bent ventrad (lateral view), moderately broad and evenly conical from insertion to apex in lateral view, usually with more than 15 trichoid setae in apical half, most of them at the inner face; most apical setae of subequal length. Male sternite IX with median strut moderately long and almost rectangularly bent subdistally; posterior portion entirely fringed with a broad, distinctly sclerotised margin; posterior margin rounded; paraprocts subequal in length, not reaching apical margin.

Ovipositor ( Figure 17 (c)). Total length ca. 560 μm. Stylus ca. 15 μm long, very slightly bent outwards, with ca. four short sensilla. Coxite ca. 240 μm long, apically moderately broadened with scattered extremely short, acute setae and four apical sensilla. Valvifer ca. 325 μm long; caudal portion slightly sclerotised and with scattered, extremely short, acute setae; fibula almost straight.

Sexual dimorphism

Females with distinct rugulose elongate elytral patches extending from elytral basis approximately to apical 0.35 and between intervals 1 and 3 (comp. Figure 16 (a,b)). Glabrous portions of metaventral disc more extended in males and entirely very broadly impressed along median suture, while rather narrow and only slightly impressed in posterior half and subanteriorly.

Differential diagnosis

Grouvellinus borneensis sp. nov. superficially resembles G. quest in its size, proportions and entirely black colour, but can be distinguished from the latter by the rather smooth, moderately densely punctate pronotum (vs. very densely punctate), the basally smoother elytral surface with only intervals 2 and 8 partly carinate (vs. intervals 3, 5, 7 and 8 crenulate-carinate). From all known Bornean Grouvellinus spp., G. borneensis sp. nov. differs by the large eyes (eye diameter larger than ID vs. smaller than ID), the sexual dimorphism in the mediobasal elytra (but presumably also present in the still unnamed species G. sp.1.). Furthermore, it is easily recognisable by its aedeagus with median lobe slightly conical in apical half, then abruptly tapered towards the slender apex, the short aedeagal base and the long parameres with about 15 equally long setae.

The species varies by about 15 – 18% genetic distance (654 bp CO1 barcode) from the known Bornean congeners.

Distribution

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

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

( Figures 7 , 16 (a – c), 17(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 (a,e)).

Type material. Holotype 3 [H7] (SP): ‘ MALAYSIA: Sabah: Tawau River; Light trap near Park Headquarter ; 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: 9 3, 4♀ (SP) same data as holotype; 13, 1♀ [H49] (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 species is named for the island of Borneo, where it is most likely endemic.

Description

Body elongate obovate, males 1.50 – 1.56 mm, females 1.60 – 1.67 mm long (CL), males 0.74 – 0.78 mm, females 0.80 – 0.83 mm wide (EW), 2.0 times as long as wide (CL/EW).

Dorsal colouration ( Figure 7 ) almost entirely dark brown to black, only tarsi, antennae and maxillary palps golden brown; pubescence pale brown. Ventral side ( Figure 16 (b,c)) brown to pale brown.

Head ( Figure 16 (a,b)) in males 0.33 – 0.35 mm, in females 0.37 – 0.39 mm wide (HW); ID 0.14 – 0.17 mm; frons, clypeus, and labrum sparsely pubescent, slightly denser in lateral portions; punctures very small and scattered; intervals flat, glabrous. Frontoclypeal suture almost straight. Eyes large (eye diameter larger than ID), very slightly protruding. Antennae genus-typical.

Pronotum ( Figure 16 (a)) in males 0.44 – 0.45 mm, in females 0.46 – 0.50 mm long (PL), in males 0.52 – 0.56 mm, in females 0.59 – 0.63 mm wide (PW), wider than long (PL/PW), widest basally, narrower than elytra, anteriorly attenuate; anterior margin moderately convex; pronotal disc slightly vaulted; entire pronotum moderately densely punctate; punctures small and shallowly impressed; setae moderately short; median carina absent; pair of posteriormedian rugose patches distinct; sublateral carinae indistinct and short; laterobasal impression shallow, rugulose; oblique impressions shallow, partly rugulose, extending obliquely from anterior 0.2 – 0.6, then continuing aside sublateral carinae up to posterior margin; entire anterior portion and portion between sublateral carinae and posterior-median patches glabrous; disc anterior of these patches slightly rugose. Hypomeron very densely punctate.

Prosternum ( Figure 16 (c)) short; lateral portions with inconspicuous plastron pubescence; median portion including process very shallowly impressed, slightly rugulose; prosternal process subquadrate.

Scutellum ( Figure 16 (a)) subcordiform, flat, rugose, with few setiferous punctures. Elytra ( Figure 7 ) elongate, moderately convex dorsally, in males 1.07 – 1.10 mm, in females 1.22 – 1.24 mm long (EL), in males ca. 1.4 times, in females ca. 1.3 times as long as wide (EL/ EW), conspicuously widest at anterior 0.6, slightly attenuating anteriad, roundly attenuating posteriad; apices wide, almost conjointly rounded; with eight longitudinal, slightly impressed rows of primary punctures (striae); primary punctures large and moderately deeply impressed at median disc, slightly smaller in basal portion and increasingly smaller and more shallowly impressed apicad, regularly arranged in median rows, less regularly arranged in lateral rows; interstices and interval rugose; interval 8 with (genus-typical) serrate carina; interval 2 slightly carinate; all intervals with setiferous secondary punctures (inconspicuous due to rugose surface); pubescence yellowish, consisting of moderately large, erected setae and small adpressed setae; lateral elytral margin more or less distinctly serrate.

Mesoventrite ( Figure 16 (c)) with 2 pairs of subtrapezoidal grooves, median pair shallowly impressed, lateral pair (behind procoxae) deeply impressed. Metaventrite ( Figure 16 (d)) with distinct median suture over the entire length. Median disc glabrous, slightly dimorphic between sexes; lateral and marginal portions moderately densely covered with setiferous tubercles and inconspicuous plastron.

Ventrite 1 ( Figure 16 (d)) comparably short; carinae bordering glabrous disc oblique and rather inconspicuous; ventrites 1 – 2 only glabrous in most anteriomedian portion; lateral portions of ventrites 1 – 2 and entire ventrites 4 – 5 moderately densely covered with setiferous tubercles and inconspicuous plastron; apical margin of ventrite 5 fringed with pubescence.

Legs ( Figure 7 ) approximately of the same length as body; tibiae longer than tarsi and femora; trochanter, femura and tibiae almost entirely densely covered with setiferous tubercles and plastron setae except almost glabrous outer, dorsal face of tibiae and inner face of tibiae and femora. Mesofemur with loose fringe of short trichoid setae on the anterior – dorsal ridge. Legs not conspicuously varying between sexes.

Aedeagus ( Figure 17 (a,b)) ca. 510 μm long, ca. 115 μm wide. Phallobase slightly asymmetrical basally, reaching ca. basal 0.31 of total aedeagus length. Median lobe moderately wide (ventral view), moderately overreaching parameres and ventral sac, very slightly conical in apical half, then abruptly tapered at the level of paramere tips towards slender apex; apex slightly bent ventrad (lateral view). Ventral sac internally densely stippled and with dense fringe of moderately short, thin and comparably delicate spines; few of those overreaching apical fringe. Parameres moderately shorter than median lobe and distinctly bent ventrad (lateral view), moderately broad and evenly conical from insertion to apex in lateral view, usually with more than 15 trichoid setae in apical half, most of them at the inner face; most apical setae of subequal length. Male sternite IX with median strut moderately long and almost rectangularly bent subdistally; posterior portion entirely fringed with a broad, distinctly sclerotised margin; posterior margin rounded; paraprocts subequal in length, not reaching apical margin.

Ovipositor ( Figure 17 (c)). Total length ca. 560 μm. Stylus ca. 15 μm long, very slightly bent outwards, with ca. four short sensilla. Coxite ca. 240 μm long, apically moderately broadened with scattered extremely short, acute setae and four apical sensilla. Valvifer ca. 325 μm long; caudal portion slightly sclerotised and with scattered, extremely short, acute setae; fibula almost straight.

Sexual dimorphism

Females with distinct rugulose elongate elytral patches extending from elytral basis approximately to apical 0.35 and between intervals 1 and 3 (comp. Figure 16 (a,b)). Glabrous portions of metaventral disc more extended in males and entirely very broadly impressed along median suture, while rather narrow and only slightly impressed in posterior half and subanteriorly.

Differential diagnosis

Grouvellinus borneensis sp. nov. superficially resembles G. quest in its size, proportions and entirely black colour, but can be distinguished from the latter by the rather smooth, moderately densely punctate pronotum (vs. very densely punctate), the basally smoother elytral surface with only intervals 2 and 8 partly carinate (vs. intervals 3, 5, 7 and 8 crenulate-carinate). From all known Bornean Grouvellinus spp., G. borneensis sp. nov. differs by the large eyes (eye diameter larger than ID vs. smaller than ID), the sexual dimorphism in the mediobasal elytra (but presumably also present in the still unnamed species G. sp.1.). Furthermore, it is easily recognisable by its aedeagus with median lobe slightly conical in apical half, then abruptly tapered towards the slender apex, the short aedeagal base and the long parameres with about 15 equally long setae.

The species varies by about 15 – 18% genetic distance (654 bp CO1 barcode) from the known Bornean congeners.

Distribution

This species is only known from 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 14. Grouvellinus luciaensis, sp. nov. (paratypes): (a) anteriodorsal aspect with pronotum; (b) anterioventral aspect with head and prosternum; (c) ventral aspect with prosternum and mesoventrite, (d) posterioventral aspect with metaventrite and ventrites 1–5.

Figure 15. Grouvellinus luciaensis, sp. nov. (paratypes): (a) aedeagus, lateral; (b) aedeagus, ventral; (c) ovipositor (half), ventral. Scale bar = 0.1 mm.

Figure 16. Grouvellinus borneensis, sp. nov. (paratypes): (a) anteriodorsal aspect with pronotum and elytra; (b) ventral aspect with prosternum and mesoventrite; (c) posteriodorsal aspect with metaventrite and ventrites 1–5.

Figure 17. Grouvellinus borneensis, 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 6–9. Habitus of the Grouvellinus species collected from the Tawan Hills Park. 6: G. luciaensis, sp. nov. (paratype male from Lucia River); 7: G. borneensis, sp. nov. (paratype male from Tawau River environment); 8: G. sp.1 (female from Tawau River environment); 9: G. sp.2 (female from Lucia River). Scale: 1 mm.