Mesoceration castaneum, 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 : 201-202

Mesoceration castaneum sp. nov. ( Figs 2 , 3 & 8 )

Type locality. South Africa, Northern Cape, Bokkeveld Plateau, Oorlogskloof Reserve, temporary stream nr. Groot Tuin , 720 m, 31 26 47.32S, 19 0 4 12.00E ( Fig. 8 B).

Type material. Holotype (male): “ 8/x/2015 South Africa NC// Oorlogskloof Reserve—pools in// temporary stream nr. Groot Tuin // 720 m 31 26 47.32S, 19 0 4 12.00E // D T Bilton leg.” (genitalia extracted and mounted on same card) and red holotype label ( AMG) .

Description. Size: Holotype: BL 1.50 mm; EL 1.05 mm; EW 0.70 mm.

Colour: Dorsum ( Fig. 2 B) with head black; ocelli, anteocellar sulci and areas between these and compound eyes paler, pitchy-brown. Pronotum chestnut brown, paler on explanate lateral portions. Elytra chestnut brown, suture and carinae darker; explanate lateral margins paler. Maxillary palpi dark chestnut brown, apical segment weakly infuscated. Legs pale brown, tarsi somewhat darker. Venter pale chestnut brown; meso- and metaventrite and abdominal ventrites darker.

Head: Labrum quadrate, widening anteriorly. Rounded apicolaterally, with v-shaped apicomedian emargination extending 0.4 of length. Sides of apicomedian emargination and anterior margins raised. Surface weakly shining, with isodiametric microreticulation and sparse punctures. Long, white recumbent setae along lateral and anterior margins. Clypeus shining, with open isodiametric microreticulation, deeper laterally, and sparse, fine punctures bearing decumbent setae. Frontoclypeal suture weakly arcuate. Frons shining, with shallow isodiametric microreticulation and medium coarse punctures bearing decumbent setae. Anteocellar sulci broad, open anteriolaterally; sulci and areas between these and compound eyes with rugulose microreticulation. Ocelli shining. Compound eyes moderately large, occupying 0.4 lateral margin of head, 12 ommatidia in longest series.

Pronotum: Cordate, transverse, broadest at middle. Anterior margin arcuate over median 0.5, without hyaline border; posterior margin weakly bisinuate around centre. Anterior angles broadly rounded; posterior angles obtusely rounded. Lateral margins sinuated from widest point to base; broadly marginated and moderately serrate. Upper surface shining with isodiametric microreticulation; shallow in reliefs, more strongly impressed in foveae. Reliefs with shallow, medium, medium punctures bearing fine, white decumbent setae. Irregular fields of coarser punctures close to anterior and posterior margins. With 10 distinct foveae as follows: Anterior median fovea elongate, deepest in middle; posterior median fovea elongate oval, deepest anteriorly. Anterior admedian foveae shallow oval, opening anteriorly; posterior admedian foveae shallow, elongate oval, orientated anteriolaterally. Anterior and posterior adlateral foveae rounded, open laterally.

Elytra: Elongate oval, broadest behind middle. Weakly rounded to subparallel over median 0.5, then attenuated to truncately rounded apices, weakly emarginated at suture. Sides broadly explanate. Punctures of elytral series evident to apex; larger in anterior 0.5, smaller and shallower posteriorly. Discal series weakly striate impressed in anterior 0.6. Serial punctures with fine decumbent setae arising from granules on anterior puncture margin, reaching next puncture in row. Series 1 and 2 confluent just behind posterior declivity. Series 5 and 6 confluent at middle. Intervals shining, granulate, granules bearing short, white decumbent setae. Interval 8 strongly carinate from shoulder to close to apex.

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

Venter: Mentum shining, with elongate microreticulation, meshes more elongate and more strongly impressed towards lateral margins. Submentum shining, with shallow isodiametric microreticulation and sparse, fine punctures bearing fine decumbent setae. Genae shining, with weakly transverse microreticulation. Gula shining, with transverse microreticulation. Prosternum with weak central ridge; surface rugulose, with dense hydrofuge vestiture. pronotal hypomeron broad, shining, with shallow isodiametric microreticulation. Meso and metaventrite with dense hydrofuge vestiture. Mesoventral plaques weak, low, forming inverted Y, stem 0.5 length of arms. Weak admedian and adlateral ridges also present.

Metaventrite with broad, shallow median fovea over posterior 0.6; fovea with hydrofuge vestiture but with small, shining glabrous patch present at apex, between metacoxae. Elytral pseudepipleurs broad, shining, without evident microreticulation; extending to apex of abdominal ventrite 5. Elytral epipleurs shining, narrow, ridge-like. Abdominal ventrites 1–4 with dense hydrofuge vestiture; small, shining, semi-glabrous areas posteromedially on ventrites 1–3. Abdominal ventrite 5 with dense hydrofuge vestiture except for semicircular glabrous patch in posterior 0.5 of centre. Abdominal ventrite 6 glabrous, shining, with shallow transverse microreticulation and irregular transverse row of punctures bearing golden decumbent setae 0.4 from posterior margin.

Aedeagus: Elongate, with parameres attaching close to base. Main piece slightly curved in ventral view, with broad, blunt tooth on left hand side of apex. Distal lobe elongate, strongly curved ventrally, extending to apex of longest setae of paramere apices ( Fig. 3 B).

Female: Unknown.

Differential diagnosis. A member of the truncatum group sensu Perkins & Balfour-Browne (1994). M. castaneum sp. nov. would key to M. rufescens Perkins & Balfour-Browne, 1994 in this work, on the basis of the chestnut colour of the pronotum and elytra. The new species differs from this species in the relatively broad, flat habitus, the weakly microreticulate pronotal reliefs and the aedeagus, which is most similar in appearance to the broadly sympatric M. umbrosum Perkins, 2008 . M. castaneum sp. nov. most closely resembles M. rugulosum Bilton, 2015 in general appearance, but differs from this species in having a much broader habitus, and a more strongly shining upper surface, as well as in the very different aedeagus.

Distribution. To date known only from the type locality (Site 13), a pool in a drying stream over sandstone rock close to the Groot Tuin entrance of Oorlogskloof Reserve. Here it occurred with Prosthetops wolfbergensis Bilton, 2013 , Pterosthetops hawequas Perkins, 2008 , Mesoceration hantam Bilton, 2014 , Pneuminion endroedyi Perkins, 2004 and P. velamen Perkins, 1997 .

Etymology. Named in reference to the glossy chestnut brown colour of the dorsum.

Figures

FIGURE 2. Habitus of hydraenid holotypes. A) Parasthetops porcellus sp. nov.; B) Mesoceration castaneum sp. nov.; C) M. chasmum sp. nov.; D) M. sabulosum sp. nov.

FIGURE 3. Aedeagi of hydraenid holotypes, ventral and lateral views. A) Parasthetops porcellus sp. nov.; B) Mesoceration castaneum sp. nov.; C) M. chasmum sp. nov.; D) M. sabulosum sp. nov.

FIGURE 8. Habitats on the Bokkeveld Plateau. A) Oorlogskloof Canyon, pools in stream above Papkuilsfontein Waterfall (Site 12); B) Oorlogskloof Reserve, stream pools close to Groot Tuin entrance (Site 13); C) Oorlogskloof Reserve, spring pool at head of stream at Groot Tuin (Site 14). Photos D. T. Bilton.