Pterosthetops chrysomallus, Bilton, David T., 2017

Bilton, David T., 2017, Water beetles from the Bokkeveld Plateau: a semi-arid hotspot of freshwater biodiversity in the Northern Cape of South Africa, Zootaxa 4268 (2), pp. 191-214 : 192-195

Pterosthetops chrysomallus sp. nov.

( Figs 1 & 5 )

Type locality. South Africa, Northern Cape, Bokkeveld Plateau, Oorlogskloof Canyon, wet rock faces below Driefontein Waterfall , 640m, 31 30 41.85S 19 0 6 58.98E ( Fig. 5 C–D).

Type material. Holotype (male): “ 7/x/2015 South Africa NC// Oorlogskloof Canyon—wet rock faces below Driefontein // Waterfall, 640m, 31 30 41.85S // 19 0 6 58.98E D T Bilton leg.” (genitalia extracted and mounted on same card) and red holotype label ( AMG) .

Paratypes (29): 16 ♂, 12♀ same data as holotype ; 1 ♂ “ 6/x/2015 South Africa NC// Avontuur Reservetemporary // stream below Fynbos Cottage // 765m 31 16 14.67S // 19 0 2 53.02E D T Bilton leg.” All with red paratype labels ( AMG, CDTB, MCZ, NMW, SAM, SANC, TMSA) .

Description. Size: Holotype: BL 2.9 mm; EL 1.85 mm; EW 1.1 mm. Paratypes: ♂ s BL 2.9–3.35 mm; EL 1.85–2.0 mm; EW 1.05–1.15 mm. ♀ s BL 3.1–3.2 mm; EL 2. 0–2.15 mm; EW 1.2–1.25 mm.

Colour: Dorsum ( Fig. 1 A) dark brown to black, with a greenish metallic sheen and long recumbent-decumbent golden setae on head, pronotum and elytra. Ocelli chestnut brown. Maxillary palpi dark brown, darker apically than basally. Legs pale yellowish brown; femorotibial junctions and tarsi darker. Venter dark piceous brown; elytral epipleurs, pronotal hypomera and underside of head paler. Prosternum, meso- and metaventrites, and much of abdomen silvery or golden due to hydrofuge vestiture.

Head: Labrum transverse, broadly rounded over anterolateral angles, with broad, shallow apicomedian emargination occupying approx. 0.2 of length. Anterior margin strongly raised and recurved posteriorly, particularly so close to apicomedian emargination. Surface of labrum shining, with shallow, somewhat obsolete microreticulation and moderate, shallow punctures, each puncture bearing a long, white decumbent seta arising from a tubercle at its anterior margin. Clypeus shining, with shallow, broad isodiametric microreticulation and moderate punctures, which are deeper than on labrum, each bearing a long, white decumbent seta. Fronto-clypeal suture deep, arcuate. Frons shining, without visible microreticulation and with coarse, dense, shallow punctures, each bearing a long, white decumbent seta, arising from anterior margin. Anteocellar sulci deep and short, extending 0.5 distance between anterior margins of ocelli and lateral margins of head. Ocelli small, shining. Compound eyes relatively large, occupying 0.4 lateral margin of head, 15 ommatidia in longest series.

Pronotum: Cordate, transverse, broadest just behind middle, arched on disc, with strongly explanate sides. Anterior margin arcuate with narrow hyaline border over median 0.3, posterior margin sinuated around centre. Anterior angles obtusely rounded, posterior angles obtuse. Lateral margins sinuated from widest point to base; narrowly marginated and weakly crenulated, with tuberculate, setose punctures. Discal reliefs shining, with traces of isodiametric microreticulation anteriorly; central 0.3 of pronotum with strong, transverse microreticulation immediately behind hyaline border. Lateral explanate areas smooth and shining, with traces of wrinkle-like microreticulation. Disc with medium, coarse punctures, each bearing a pale recumbent-decumbent seta arising from the anterior margin of the puncture; punctures becoming shallower and more evidently tuberculate laterally. Lateral explanate areas with decumbent setae arising from small tubercles. Pronotum with 10 distinct foveae as follows: Anterior median fovea elongate, shallower posteriorly; posterior median fovea shallow, rounded, impunctate; two median foveae separated by approx. diameter of posterior fovea. Anterior admedian foveae obsolete, open, reduced to shallow groove formed by partial coalescence of somewhat larger punctures; posterior admedian foveae shallow, punctate, opening anteriolaterally. Anterior and posterior adlateral foveae sham, rounded and pit-like; connected by shallow longitudinal sulcus.

Elytra: Elongate oval, broadest just behind middle. Sides weakly rounded, gradually attenuated to shoulder and apex. Apices rounded, emarginated at suture. Sides narrowly explanate, entire. Each elytron 10-seriate punctate, with a broad, shallow, transverse depression (saddle) occupying intervals 2–4, 0.25 behind shoulders, running for approx. 0.2 of elytral length. Punctures of elytral series not markedly larger and often shallower than those of intervals, giving appearance of close punctation throughout elytra. Punctures of series and intervals with long, pale decumbent setae arising from tubercles at their anterior margins. Punctures of discal intervals arranged in two irregular rows over anterior 0.25. Series 1–3 weakly striate-impressed. Entire elytral surface shining, with some fine wrinkles but no evident microreticulation.

Venter: Mentum shining, strongly microreticulate, meshes isodiametric in centre and elongate at sides. Long, pale yellow recumbent setae along anterior margins. Surface with sparse, coarse punctures, each bearing a flattened, white decumbent seta. Submentum shining, with coarse, open microreticulation posterolaterally, and sparse medium punctures bearing decumbent setae. Genae shining, impunctate, shallow, transverse microreticulation restricted to areas close to lateral margins. Gula shining, impunctate, with transverse microreticulation posteriorly and laterally. Prosternum with weak central ridge, more evident posteriorly. Surface rugulose, covered in dense hydrofuge vestiture; short, white and decumbent centrally, longer, golden and recumbent laterally, extending to border of hypomeral antennal pocket. Pronotal hypomeron broad, shining, with shallow isodiametric microreticulation. Mesoventrite and metaventrite with hydrofuge vestiture; dense, long and golden on metaventrite, shorter, sparse and whiter on mesoventrite. Mesoventral plaques with vestiture, weak, forming inverted Y, but arms scarcely visible. Weak admedian and adlateral ridges also present. Metaventrite with shallow elongate median fovea over posterior 0.5; fovea flanked by broad, glabrous patches which extend to posterior margin and connect in a narrow glabrous band apicomedially, anterior to metacoxae. Elytral pseudepipleurs narrowing approx. 0.25 from apex; shining, impunctate, with traces of fine wrinkles; epipleurs shining, ridge-like. Abdominal ventrites 1–4 fringed with long, closely-set squamiform setae at hind margins, setae clearly overlapping following ventrite. Abdominal ventrite 1 clothed with dense, golden hydrofuge vestiture except for semicircular glabrous patch occupying central 0.3 of hind margin and extending anteriorly over a maximum of 0.5 length if segment. Glabrous area shining, with shallow, somewhat obsolete microreticulation. Abdominal ventrites 2–5 glabrous except for narrow patch of dense, golden hydrofuge vestiture towards lateral margins. Glabrous areas with shallow, isodiametric microreticulation and irregular, transverse row of fine punctures, bearing long, fine, white decumbent setae. Abdominal ventrite 6 glabrous, with shallow, open, transverse microreticulation; posterior 0.6 with dense, coarse, deep punctures, arranged in four irregular transverse rows, each puncture bearing a long, fine, white decumbent seta.

Aedeagus: Elongate, arcuate in lateral view, with parameres attaching close to base and extending just beyond apex of the main piece. Main piece produced on left side in ventral view, thus appearing somewhat notched due to gap between this projection and the distal lobe. Distal lobe elongate, curved dorsally, extending beyond apices of paramere setae ( Fig. 1 B).

Female: Somewhat broader than makes, with broader, more explanate elytral margins. Microreticulation somewhat more evident on pronotum. Abdominal ventrite 6 more strongly punctate at apex. Otherwise as male.

Variation: Paratypes vary somewhat in size and colouration, some being slightly darker, others slightly paler than the holotype.

Differential diagnosis. Apparently a rather isolated species, which at 2.9–3.35 mm is the largest known member of the genus; the closest in body size described to date being P. uitkyki Bilton, 2014 , which ranges up to 2.65 mm. In addition to its large body size, P. chrysomallus sp. nov. is clearly distinguished from all known Pterosthetops by its elytral punctation and characteristic aedeagus.

Distribution. To date known from only two localities on the Bokkeveld Plateau (Sites 5 & 9), close to Neiuwoudtville. At Driefontein this was by far the most abundant beetle in the waterfall splash zone, where it occupied a madicolous microhabitat typical of most species of the genus ( Bilton, 2014b; Bilton 2016). At Avontuur a single specimen was found where a small, dry stream joined the Grasberg River. Here there were rock outcrops, which would have supported seepages at times of higher water flow earlier in the year.

Etymology. From the Greek chrysomallon (= golden haired) in reference to the Golden Fleece of Greek mythology and the golden hairs found on both the dorsum and venter of this species.

Figures

FIGURE 1. Pterosthetops chrysomallus sp. nov. A) Holotype habitus; B) aedeagus in ventral and lateral views.

FIGURE 5. Habitats on the Bokkeveld Plateau. A) Avontuur Reserve, margins of Kromvlei (Site 8); B) Avontuur Reserve, pools in drying stream (Site 7); C) Oorlogskloof Reserve, wet rocks & stream below Driefontein Waterfall (Sites 9 & 10; stream below large boulders in photo); D) Oorlogskloof Reserve, wet rocks below Driefontein Waterfall (Site 9 — with Andy Foggo). Photos D. T. Bilton.