Mesoceration piketbergense, Bilton & Mlambo, 2019

Bilton, David T. & Mlambo, Musa C., 2019, Two new Mesoceration Janssens, 1967 from the Piketberg, South Africa (Coleoptera, Hydraenidae), Zootaxa 4555 (2), pp. 268-274 : 273-274

Mesoceration piketbergense sp. nov.

Type locality. South Africa , Western Cape Province, Piketberg, stream below Sebrakop , 32° 46’ 19.35’’S // 18° 45’ 42.09’’E, 809 m.

Type material. Holotype (male): " 3/x/2015 South Africa WC// Piketberg - stream below// Sebrakop 32 46 19.35S // 18 45 42.09E 809 m // D T Bilton leg." (genitalia extracted and mounted on same card) and red holotype label (AMG).

Paratypes (20): South Africa: 5♂, 15♀, same data as holotype .

Description. Size: Holotype: BL 1.90 mm; EL 1.12 mm; EW 0.63 mm. Paratypes: Males BL 1.80–1.96 mm; EL 1.05–1.15 mm; EW 0.60–0.65 mm. Females BL 1.75–1.95 mm; EL 1.05–1.10 mm; EW 0.60–0.65 mm.

Colour: Dorsum ( Fig. 1B ) black with a rim of dark yellow-brown on the anterior margins of labrum. Anterior and posterior margins of pronotum and lateral margins of elytra dark brown; ocelli dark brown. Maxillary palps pale yellow, last segment slightly infuscated over apical 0.6. Legs orange brown. Venter black with silvery hydrofuge vestiture. Prementum pale brown; submentum darkish brown; gena black; gula black, slightly paler basally.

Head: Labrum slightly transverse, rounded apicolaterally with broad apicomedian emargination running approx. 0.4 of length. Surface shining with fine microreticulation; elongate in centre, isodiametric basally; with scattered fine punctures bearing recumbent setae. Frontoclypeal suture obsolete. Clypeus with strong, transverse microreticulation over central part, and scattered, medium punctures bearing short, white recumbent setae. Frons and vertex dull, with strong granulate microreticulation and scattered medium punctures bearing white recumbent setae. Ocelli small, shining. Head behind ocelli with sharp declivity. Anteocular sulci broad, shallow, open apicolaterally. Compound eyes small, occupying ca. 0.35 side of head; 10 ommatidia in longest series.

Pronotum: Cordate, slightly transverse, broadest before middle. Anterior margin arcuate over median 0.5, no hyaline border; posterior margin bisinuate around centre. Anterior angles obtusely rounded; posterior angles obtuse and weakly rounded. Lateral margins sinuated from widest point to base, broadly marginated and moderately serrate. Surface dull, with dense coarse punctures bearing long, fine, decumbent setae. Relief with shining granulate microreticulation. With 10 foveae as follows: anterior median fovea elongate, posterior median fovea elongate oval, both deepest in centre and confluent. Anterior admedian foveae shallow, oval, open anteriorly; posterior admedian foveae deeper, elongate oval, orientated anterolaterally. Anterior adlateral foveae oval, shallow, open apicolaterally. Posterior adlateral foveae small, oval, open anterolaterally.

Elytra: Elongate oval, broadest at middle, subparallel over anterior 0.5 then attenuated to acuminate, rounded apices. Apical angles rounded, slightly emarginated around suture. Punctures of elytral series relatively coarse, larger in anterior 0.5 and smaller and shallower posteriorly. Serial punctures with fine decumbent setae, not usually reaching next puncture in row. Weakly striate impressed on disc, especially series 1 and 2. Series 1 and 2 confluent immediately behind posterior declivity, at ca. 0.65 of length; series 5 and 6 confluent anteriorly, at ca. 0.25 of length. Intervals shining, with weak granules, bearing long, white, recumbent to decumbent setae.

Legs: Apical protarsomere with two stout ventral setae; basal three protarsomeres with suction setae.

Wings: Reduced, approx. 0.5 length of elytra when extended.

Venter: Mentum weakly shining, with rugulose microreticulation, meshes elongate along lateral margins and isodiametric in centre; surface with scattered, erect setae, particularly around front margins. Submentum with transverse microreticulation and scattered medium punctures with long recumbent setae. Genae shining, with transverse microreticulation anteriorly, covered with dense hydrofuge vestiture posteriorly. Gula weakly shining, with weak transverse microreticulation. Prosternum with glabrous ridge anteriorly, covered with transverse microreticulation and metaventrite covered with dense hydrofuge vestiture. Pronotal hypomeron broad, weakly shining with fine isodiametric microreticulation. Mesoventral plaques glabrous, forming inverted Y; admedian and adlateral ridges visible but weak. Metaventrite with shallow, elongate median fovea over posterior 0.5 and shallow oval depressions below mesocoxae; posterior margin emarginated at centre, here devoid of hydrofuge vestiture. Abdominal ventrite 5 with dense hydrofuge vestiture over anterior 0.65; glabrous posteriorly, with transverse microreticulation. Abdominal ventrite 6 entirely glabrous with weak transverse microreticulation and an irregular transverse row of long recumbent setae.

Aedeagus: Elongate, parameres attached near the base. Parameres extend beyond the main piece, to approximately 0.5 length of distal lobe. Main piece with strong, elongate tooth on left side in ventral view. Distal lobe elongate, narrow, strongly angled to the left in ventral view (see Fig. 2B ).

Female: Broader than male, especially on elytra, with more broadly explanate lateral margins. Elytral apex more strongly acuminate. Abdominal ventrite 5 with broad, glabrous patch with weak transverse microreticulation over central 0.5, tumid laterally at apical margin.

Variation: Some specimens slightly paler than holotype.

Differential diagnosis. A member of the endroedyi group sensu Perkins & Balfour-Browne (1994). In this work the species would key to Mesoceration concessum Perkins & Balfour-Browne, 1994 , being apparently close to this species and Mesoceration tabulare Perkins, 2008 . M. piketbergense sp. nov. differs from M. concessum in having a more strongly microreticulate pronotum, which is granulate on the reliefs, and denser, coarser punctures on the frons and vertex. In the new species the granules of the elytral intervals are smaller than those in M. concessum , being closer in this character to M. tabulare . The three species can readily be distinguished on aedeagal characters, particularly details of the apex of the main piece and the shape of the distal lobe. All three species are brachypterous ( Perkins & Balfour-Browne 1994; Perkins 2008).

Distribution.

So far only known from the Piketberg range, a westerly outlier of the north-south trending mountains of the Western Cape Province, South Africa. Here it was found in only one of the four streams sampled in 2015, where it was, however, abundant. As with M. concessum and M. tabulare , the species brachyptery may explain its apparent geographical restriction.

Etymology. Named in reference to the Piketberg range, in which the type locality is situated.

Figures

FIGURE 1. Mesoceration species, holotype habitus. A) Mesoceration explanatum sp. nov.; B) Mesoceration piketbergense sp. nov. Scale bar = 1 mm.

FIGURE 2. Mesoceration species, paratype aedeagi. A) Mesoceration explanatum sp. nov.; B) Mesoceration piketbergense sp. nov. Scale bar = 0.1 mm.