Necterosoma timorense, Balke & Toussaint & Hendrich & Hájek, 2013

Balke, Michael, Toussaint, Emmanuel F. A., Hendrich, Lars & Hájek, Jiří, 2013, A new species of the Australian genus Necterosoma from Timor (Coleoptera: Dytiscidae: Hydroporini), Acta Entomologica Musei Nationalis Pragae 53 (1), pp. 65-74 : 67-72

Necterosoma timorense sp. nov.

( Figs 1–7 )

Type locality. Indonesia, West Timor, Mount Mutis, 09°38′07.44″S, 124°12′48.00″E, ca. 1580 m alt.

Type material. HOLOTYPE: J: ‘Indonesia: Timor, Mt. Mutis, creeks & streams, 1580m, 1.x.1992, 09 38.124S 124 12.800E, Balke (TIM04) [printed]’, ‘ HOLOTYPE, Necterosoma , timorense sp. nov., Balke, Toussaint, Hendrich & Hajek des. 2013 [red label, printed]’ ( MZBC). PARATYPES: 40 JJ 39 ♀♀, same label data as the holotype ( ANIC, HFCB, LHCB, MZBC, NHMW, SAMA, ZSM); 2 specimens with additional ‘DNA MB 4488’ and ‘DNA MB 4489’, respectively [green label indicating the specimen with voucher number was used for DNA extraction] ( ZSM); 5 JJ 3 ♀♀, ‘ INDONESIA, W Timor, Bali prov., Soe env., Desa Nenas, Mutis Mts, 20.-28.xi.2012, 1500-1600m, J. Horák leg. [printed]’ ( NMPC). All paratypes are provided with a red printed paratype label.

Additional material. 9 larvae from ‘ Indonesia: Timor, Mt. Mutis, creeks & streams, 1580m, 1.x.1992, 09 38.124S 124 12.800E, Balke ( TIM 04)’.

Description. Male holotype. Comparatively large to other species of genus, yellowish to dark brown species, with black longitudinal markings on elytra. Body elongate, dorsoventrally flattened, widest in middle of elytra. Beetle appearance rather shiny ( Fig. 1 ).

Colouration. Head testaceous, darkened posteriorly; mouth appendages testaceous, terminal palpomere of maxillary palps piceous; antennae testaceous, antennomeres V–XI darkened apically. Pronotum dark brown with rufo-piceous lightenings along sides (broader anterolaterally). Elytra rufo-piceous with well separated black longitudinal stripes. Prosternum and metacoxal processes rufo-piceous, rest of ventral surface black. Legs testaceous; metafemora, tibiae apically and laterally, and tarsi darkened.

Sculpture ( Figs 1, 3–4 ): Head microreticulated, reticulation composed of shallowly impressed polygonal meshes. Punctation simple, punctures irregularly dispersed, with diameter bigger than that of meshes; distance between punctures smaller than their diameter; punctures coarser and denser posteriorly. Head dorsally with two clypeal grooves. Fore margin of clypeus not bordered. Sides of pronotum rounded, weakly bordered; disc convex, medially with shallow longitudinal depression. Base of pronotum with several short longitudinal grooves, and shallow transverse depression along basal margin. Punctation coarse, especially on sides; punctures sometimes confluent, thus microreticulation poorly perceptible. Row of large setigerous punctures presents along anterior margin. Surface of pronotum and elytra covered with short recumbent golden setae. Elytra without carinae. Elytral punctation coarse, microreticulation absent; longitudinal puncture lines poorly perceptible. Subapical spine on lateral margin of elytra small but distinct. Prosternal process lanceolate, distinctly keeled; not narrowed compared to other species of genus. Metacoxal lines relatively close, subparallel anteriorly; metacoxal processes covered with recumbent setae. Punctation of metaventrite, metacoxae and abdominal ventrite I coarse, punctation of abdominal ventrites II–V progressively becoming finer and denser from ventrite II to apical ventrite; microreticulation absent. Abdominal ventrites medially with tuft of long golden setae, apical ventrite covered with recumbent setae; tip of ventrite slightly produced into a weak broad spine covered with setae. Protrochanters on anterior side, mesotrochanters and mesotibiae on posterior side with long golden setae; metatibia with very long natatorial setae on posterior side, metatarsi with natatorial setae on both sides. Pro- and mesotarsi moderately expanded, protarsomere II about 1.2× as wide as long. Protibia moderately expanded with large notch on inner edge near base ( Fig. 2 ). Mesotibia expanded, quite strongly curved.

Genitalia. Median lobe of aedeagus broadly lanceolate in ventral view; its extreme tip truncate ( Figs 3–4 ). Lateral lobes (parameres) with distinct longitudinal carina and fine long striolae on outer side; apically with setae ( Fig. 5 ).

Female. Punctation of dorsal surface finer and denser than in male, thus beetle appearance matt. Microreticulation on pronotum absent. Body widest behind shoulders. Sides of pronotum converging anteriorly, nearly parallel-sided in basal two thirds; anterior angles acute, posterior angles rectangular. Sides of elytra with distinct subhumeral expansion ( Figs 6–7 ). Puncture lines on elytra more distinct than in male. Pro- and mesotarsus only little expanded, tarsomere II about as wide as long. Pro- and mesotibia simple, their inner side nearly straight. Apical ventrite as in male but spine more robust and prominent, and setae longer.

Variability. Specimens of type series vary significantly in body colouration, especially in extension of rufo-piceous lightenings of anterolateral part of pronotum, and in colour on elytra, which varies from almost totally black to having black longitudinal stripes well separated.

Measurements. Males: TL 4.9–5.3 mm (holotype 5.3 mm); TL-h 4.5–4.9 mm (holotype 4.7 mm); TW 2.4–2.6 mm (holotype 2.6 mm). Females: TL 4.8–4.9 mm; TL-h 4.4–4.5 mm; TW 2.4–2.5 mm.

Differential diagnosis. In coloration, paler specimens of N. timorense sp. nov. are close to the Australian N. penicillatum (Clark, 1862) , darker specimens resemble Australian N. schmeltzi Sharp, 1882 and N. aphrodite Watts, 1978 . From all three species, N. timorense sp. nov. can be distinguished by a distinct subhumeral expansion of the female elytra ( Figs 6–7 ), the shape of the notch on inner edge of the male protibia ( Fig. 2 ), and the shape of the median lobe ( Figs 3–4 ).

Etymology. Named after the island Timor, where the type material was collected; adjective in the nominative singular.

Collection circumstances. All specimens of N. timorense sp. nov. were collected in partly shaded rest pools of intermittent forest streams, at an altitude of 1,500 –1,600 m. The beetles were found in shallow water, among roots, twigs and submerged leaf packs ( Figs 8–10 ). Necterosoma timorense sp. nov. was found syntopically with the Gyrinidae Dineutus regimbarti regimbarti Régimbart, 1882 and Macrogyrus obliquatus Aubé, 1838 , the Dytiscidae Copelatus melanogrammus Régimbart, 1883 , Hydaticus pacificus Aubé, 1838 , Platynectes sp. , Rhantus suturalis (W. S. Macleay, 1825) and Sandracottus chevrolati Aubé, 1838 , and some unidentified Hydrophilidae of the genera Anacaena Thomson, 1859 , Enochrus Thomson, 1859 , and Helochares Mulsant, 1844 .

Distribution. Only known from the type locality on Mt. Mutis in West Timor ( Indonesia) but probably more widespread on the island.

Figures

Figs 1–7: Necterosoma timorense sp. nov. 1 – male habitus; 2 – male protibia; 3 – median lobe in ventral view; 4 – median lobe in lateral view; 5 – right lateral lobe (paramere); 6 – female habitus in dorsal view; 7 – female habitus in ventral view. Scale bar (Figs 3–5): 0.5 mm.

Figs 8–10: Indonesia, West Timor, track to Mt. Mutis. Rest pools of an intermittent creek in mixed eucalypt forest (Eucalyptus urophylla S. T. Blake). Type locality of Necterosoma timorense sp. nov.