Mesoceration hantam, Bilton, David T., 2014

Bilton, David T., 2014, Two new water beetles from the Hantamsberg, an inselberg in the Northern Cape of South Africa (Coleoptera, Hydraenidae), Zootaxa 3887 (3), pp. 471-480 : 472-474

Mesoceration hantam sp. nov.

( Figs 1–3 )

Type locality. South Africa, Northern Cape, Calvinia, Hantamsberg, drying stream with coarse gravel on NW side of summit plateau, 31° 22’ 57.26’’S 19° 46’ 22.97’’E, 1,500 m ( Fig. 3 A).

Type material. Holotype (male): “ 18/ix/2010 South Africa NC// Calvinia Hantamsberg summit// drying stream on gravel on NW side// of plateau— 1,500 m D T Bilton leg.” (genitalia extracted and mounted on same card) and red holotype label ( SAM).

Paratypes (15): South Africa: 8 ♂, 5 ♀ “ 18/ix/2010 South Africa NC// Calvinia Hantamsberg summit// drying stream on gravel on NW side// of plateau— 1,500 m D T Bilton leg.” ( CDTB, NMW, SANC, TMSA); 1 ♂ “ 18/ix/2010 South Africa NC// Calvinia Hantamsberg summit// pools in stream 1 km N of// mast 1,500 m D T Bilton leg.”; 1 ♀ “ 18/ix/2010 South Africa NC// Calvinia Hantamsberg summit// pools with Bulbinella beside// track 1,500 m D T Bilton leg.” All with red paratype labels.

Description. Size: Holotype: BL 1.8 mm; EL 1.1 mm; EW 0.6 mm. Paratypes: ♂s BL 1.7–1.85 mm; EL 1.06–1.1 mm; EW 0.56–0.62 mm. ♀s BL 1.8–1.83 mm; EL 1.13–1.15 mm; EW 0.63–0.65 mm. Dorsum ( Fig. 1 A)—head and pronotum dark piceous brown to black. Elytra chestnut brown, with diffuse piceous patches around shoulders, along suture, over elytral intervals 8-10 and on basal 0.3 of intervals 1-2. Legs chestnut brown, maxillary palpi dark brown, with apical segment more strongly infuscated. Venter piceous with silvery hydrofuge vestiture and paler pseudepipleurs and epipleurs.

Head: Labrum slightly transverse, expanded apically and rounder apicolaterally, with well-marked apicomedian emargination, running approx. 0.5 of length. Sides of apicomedian emargination weakly raised. Surface of labrum shining, with weak microreticulation composed of elongate meshes, whose long axes follow the borders of the sclerite. Microreticulation obsolete on centre of labrum and immediately inside apicomedian emargination; strongest inside lateral margins. Labrum with fine, sparse, shallow punctures on central portion. Entire upper surface of head shining, central 0.5 of clypeus, frons and vertex lacking microreticulation, which is restricted to lateral portions of the head capsule, being particularly strong on clypeus and within and to the outside of the well-marked oblique sublateral impressions. Microreticulation composed of transverse meshes. Frontoclypeal suture shallow but distinct. Smooth area of head with small, shallow, sparse punctures, each bearing a small, peg-like seta. Oblique sublateral impressions with coarser, denser, larger punctures. Ocelli well-marked, chestnut-brown; paler than head. Eyes large and pronounced, occupying just under 0.5 length of head, with 11-12 convex facets in longest series. Maxillary palpi elongate, approx. 1.5x length of head.

Pronotum: Cordate, widest at middle; anterior margin weakly arcuate over central 0.66, without hyaline border. Anterior angles rounded, posterior angles almost rectangular. Lateral margins finely bordered, with irregular crenulations outside borders. Disc weakly convex, strongly shining, with fine, shallow sparse punctures, more widely spaced and somewhat smaller than those on head. Lacking microreticulation except for a narrow band of shallow transverse meshes along central 0.5 of anterior margin. With 10 distinct foveae as follows: two median foveae, anterior elongate and narrower posteriorly, posterior transverse, double laterally; two admedian foveae on each side, anterior shallow, with large, coarse punctures, posterior obliquely elongate; two adlateral foveae on each side, posterior deeper than anterior, both opening laterally. Sparse, coarse punctures anterior to anterior foveae, punctures merging into foveae themselves. Double row of coarse, sparse punctures along posterior pronotal margin; anterior row deeper and larger than posterior.

Elytra: Elongate-oval, broadest in middle and parallel-sided over much of length. Apices truncate, co-jointly rounded to centre. Base wider than base of pronotum. Humeral angles rounded; sides smooth, lacking visible crenulations and weakly explanate over median 0.7. Each elytron slightly depressed at base, with a transverse row of three very large punctures. Serial punctures largest on disc, becoming smaller both posteriorly and anteriorly, especially anteriorly in series 2. Largest serial punctures separated by about their own diameter. Series 1-2 becoming confluent at middle. All series striate impressed, striae being deeper laterally. Series 5-6 confluent for a single puncture approx. 0.3 behind basal margin of elytra. Intervals flat, strongly shining. Eighth interval sharply costate from shoulder almost to apex; costa steeper on internal side. Intervals with longitudinal row of small, shallow punctures, each bearing a short, decumbent seta.

Venter: Mentum, submentum, genae and gular region shining. Mentum with elongate microreticulation around margins; centre smooth and with scattered medium shallow punctures in posterior 0.5, each bearing a long decumbent seta. Submentum with similar scattered setose punctures. Genae smooth, with coarse, transverse corrugations. Gula with transverse microreticulation, becoming more strongly impressed towards posterior margin. Prosternum with a smooth broad low central ridge, flanked by two shallow, open depressions. Surface finely reticulate, with a dense hydrofuge vestiture, densest anteriolaterally. Pronotal hypomera broad, shining, lacking visible microreticulation. Meso and metaventrites with dense hydrofuge vestiture, densest laterally. Mesoventral plaques restricted to median ridge, expanded triangularly posteriorly, weakly shining. Elytral pseudepipleurs broad, flat, shining, with trace of obsolete microreticulation anteriorly. Epipleurs narrow and ridge-like, shining. Abdominal ventrites 1–4 covered in dense hydrofuge vestiture; ventrite 5 with same vestiture anteriorly and glabrous semicircular area posteriorly. Glabrous portion of ventrite 5 shining, lacking microreticulation, with transverse row of coarse shallow punctures, each bearing a long decumbent seta. Ventrite 6 entirely glabrous, with weak transverse microreticulation anteriorly. Posterior portion of ventrite 6 with coarse shallow punctures, arranged in three irregular transverse rows, each puncture bearing a long decumbent seta.

Legs: Moderately long and slender. Apical protarsomere with four stout spine-like setae ventrally.

Aedeagus: Strongly elongate, with parameres attaching close to base and extending well beyond the apex of the main piece, almost to the apex of the distal lobe. Main piece with asymmetrical apex extending into a tooth-like process, and a long, curved, tube-like distal lobe. ( Fig. 1 C).

Female: Elytral apices broader, more truncate than in males; lateral explanate margins broader in most specimens. Transition between anterior vestiture and posterior glabrous area on abdominal ventrite 6 more abrupt, marked by a distinct ridge. Tarsi shorter, particularly protarsi. Ventral setae of apical protarsomere shorter and finer.

Variation: Paratypes vary somewhat in colouration and the degree of confluence between the punctures of elytral series 5 and 6, which sometimes remain separate despite almost touching.

Differential diagnosis. A member of the rivulare group sensu Perkins & Balfour-Browne (1994) and Perkins (2008). Mesoceration hantam sp. nov. is closest to M. splendorum Perkins & Balfour-Browne , both externally and on genitalia. It differs from this species particularly in the somewhat larger size (1.7–1.85 mm vs. ca. 1.6 mm), confluence between elytral series 1 and 2 occurring more posteriorly and confluence of elytral series 5 and 6 involving fewer punctures or absent. The aedeagi of the two species are also distinct, that of M. hantam sp. nov. being larger, with a longer apical tooth on the main piece, and a differently shaped and more elongate distal lobe ( Fig. 1 C).

Distribution. To date known only from three localities on the summit of the Hantamsberg close to Calvinia, in Hantam Plateau Dolerite Renosterveld (sensu Mucina & Rutherford, 2006). Here the species was abundant amongst gravel and marginal vegetation in pools in two temporary stream systems investigated ( Fig. 3 A–C. The species was also present in a shallow temporary wetland over rock and clay with Bulbinella nutans (Thunb.) T. Durand & Schinz , although it occurred here in much lower numbers (see Fig. 3 D).

Etymology. Named in reference to the Hantamsberg plateau ( Fig. 2 ) where the species was discovered. Hantam is a Nama term for the red edible Pelargonium bulbs which grow in the region.

Figures

FIGURE 1. Habitus and genitalia of Hantamsberg Hydraenidae. A) Mesoceration hantam sp. nov., holotype; B) Parhydraena faeni sp. nov., holotype; C) Mesoceration hantam sp. nov., aedeagus, ventral and lateral view; D) Parhydraena faeni sp. nov., aedeagus ventral and lateral views. Scale bar A – B = 1 mm; C – D = 0.25 mm.

FIGURE 2. Southern margin of the Hantamsberg plateau, showing its isolation from the surrounding plains. The yellow flower in the foreground is likely Moraea reflexa Goldblatt, endemic to the Hantamsberg. Photo D. T. Bilton.

FIGURE 3. Water beetle habitats on the Hantamsberg plateau, 1,500 m. A) Drying stream pool on gravel on northwest side of plateau; B) pool in stream 1 km north of mast; C) detail of residual pool in same stream system; D) temporary pool on clay / rock with Bulbinella nutans. Photos D. T. Bilton.