Mesoceration sabulosum, 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 : 206-207

Mesoceration sabulosum sp. nov. ( Figs 2 , 3 , 6–8 )

Type locality. South Africa, Northern Cape, Bokkeveld Plateau, Avontuur Reserve, temporary stream below Fynbos Cottage , 765 m, 31 16 14.67S 19 0 2 53.02E ( Fig. 6 A–B).

Type material. Holotype (male): “ 6/x/2015 South Africa NC// Avontuur Reserve—temporary // stream below Fynbos Cottage // 765m 31 16 14.67S // 19 0 2 53.02E D T Bilton leg.” (genitalia extracted and mounted on same card) and red holotype label ( AMG) .

Paratypes (21) 8 ♂ 7 ♀ same data as holotype ; 4 ♂ 2 ♀ “ 8/x/2015 South Africa NC// Oologskloof Canyonstream // pools @ Papkuilsfontein 667 m // 31 33 19.56S 19 0 7 35.17E // D T Bilton leg.” All with red paratype labels ( AMG, CDTB, MCZ, SAM, SANC, TMSA) .

Description. Size: Holotype: BL 1.55 mm; EL 0.95 mm; EW 0.55 mm. Paratypes: ♂ s BL 1.40–1.55 mm; EL 0.85–0.95 mm; EW 0.55–0.60 mm. ♀ s BL 1.55–1.60 mm; EL 0.95–1.00 mm; EW 0.55–0.60 mm.

Colour: Dorsum ( Fig. 2 D) with head dark pitchy brown to black; ocelli and areas immediately surrounding them paler. Anteocellar sulci and front margins of labrum darker chestnut brown. Pronotum reddish brown on disc; lateral explanate areas paler. Elytra reddish brown, suture slightly darker. Maxillary palpi yellow, apical segment darker. Legs yellow, femorotibial junctions somewhat darker. Venter predominantly pale reddish brown; meso and metaventrite and abdominal ventrites darker.

Head: Labrum quadrate, widening anteriorly. Rounded apicolaterally, with broad v-shaped apicomedian emargination extending 0.4 of length. Sides of apicomedian emargination slightly raised. Surface weakly shining, with fine, shallow isodiametric microreticulation and sparse, fine punctures bearing decumbent setae. Clypeus weakly shining, with granulate microreticulation and scattered, fine punctures bearing white decumbent setae. Frontoclypeal suture weakly arcuate. Frons weakly shining, with shallow, granulate isodiametric microreticulation and sparse, fine punctures bearing white decumbent setae. Anteocellar sulci shallow, open anteriolaterally; reticulation stronger in furrows and between furrows and compound eyes, than on centre of frons. Ocelli shining. Compound eyes moderately large, occupying 0.5 lateral margin of head, 12 ommatidia in longest series.

Pronotum: Cordate, slightly transverse, broadest at middle. Anterior margin arcuate over central 0.5, no hyaline border; posterior margin weakly bisinuate around centre. Anterior angles broadly rounded; posterior angles rectangular. Lateral margins sinuated from widest point to base; broadly marginated and weakly serrate. Upper surface weakly shining, with fine, isodiametric microreticulation, weakly granulate on reliefs and sparse, fine punctures bearing decumbent setae. With 10 distinct fovea as follows: Anterior and posterior median foveae shallow, elongate. Anterior admedian foveae shallow, oval, open anteriorly; posterior admedian foveae shallow, elongate oval, orientated anterolaterally. Anterior adlateral foveae shallow, broadly opening to lateral margins; posterior adlateral foveae smaller, deeper, pit like.

Elytra: Elongate oval, broadest at middle. Subparallel over median 0.5, then attenuated to broadly rounded apices, weakly emarginated around suture. Narrowly explanate at sides. Punctures of elytral series evident to apex; larger in anterior 0.5, smaller behind. Discal series striate impressed; elytral disc relatively flat between carinae. Series 1 and 2 confluent at posterior declivity; 5 and 6 confluent over anterior 0.3. Discal series with granules immediately anterior to punctures, each bearing a white decumbent seta. Intervals shining, granulate, each granule with a long, white decumbent seta. Interval 8 strongly carinate from shoulder almost to apex.

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

Venter: Mentum weakly shining, with shallow transverse microreticulation and sparse, fine punctures bearing decumbent setae. Long erect setae present along anterior margin. Submentum weakly shining, with isodiametric to transverse microreticulation; impunctate. Genae weakly shining, with strongly transverse microreticulation. Gula shining in centre, with fine transverse microreticulation; rugose isodiametric microreticulation at sides. Prosternum with well-marked glabrous central ridge which widens posteriorly; remaining surface rugulose, with dense hydrofuge vestiture. Pronotal hypomeron broad, dull, with shallow, open isodiametric microreticulation. Meso and metaventrite with dense hydrofuge vestiture. Mesoventral plaques forming inverted Y, stem 0.5 length of arms.

Weak admedian and adlateral ridges also present. Metaventrite with broad, shallow median fovea over posterior 0.2; fovea without hydrofuge vestiture. Elytral pseudepipleurs broad, shining, without evident microreticulation; narrowing gradually to apex. Elytral epipleurs shining, narrow, ridge-like. Abdominal ventrites 1–5 with dense hydrofuge vestiture except for small, shining glabrous patches in centre of ventrites 1–3. Abdominal ventrite 6 glabrous, dull, with transverse microreticulation and irregular transverse row of fine, white decumbent setae 0.3 from apex; setae reaching or surpassing apex of ventrite.

Aedeagus: Relatively large compared to body size, elongate, with parameres attaching close to base. Main piece curved ventrally in lateral view, with bluntly rounded, asymmetrical apex in ventral view. Distal lobe attached dorsally, with narrow stem and expanded, irregular apex ( Fig. 3 D).

Female: Elytra broadest just behind shoulders, where explanate lateral margin is very well developed; generally wider than males, with apex more strongly acuminate around suture. Abdominal ventrite 5 with raised, ventrally-directed ridge along posterior margin. Abdominal ventrite 6 with vestiture and short, stout setae along posterior margin and long, erect setae in centre of posterior margin.

Variation: In addition to size, paratypes vary somewhat in colouration, some specimens being paler than the illustrated holotype, although this may, in part, be due to slight tenerality.

Differential diagnosis. A member of the endroedyi group sensu Perkins & Balfour-Browne (1994). The species could key to M. dissonum Perkins & Balfour-Browne, 1994 in this work since the granules of the median elytral intervals continue beyond the posterior declivity. M. sabulosum sp. nov. differs in its more elongate, parallel-sided habitus, paler dorsal and ventral colouration, duller, more strongly granulate elytra, head with stronger microreticulation on frons, and the very different aedeagus. The new species is close to M. sewefonteinense Bilton, 2015, from which it differs in the apparently slightly larger size (1.40–1.60 mm vs. 1.40 mm), more strongly marked elytral series composed of larger, deeper punctures, shallower pronotal foveae (particularly the median and admedian ones), the darker head, and the structure of the aedeagus. The aedeagal structure of these two species, with a central, dorsally-attached distal lobe, are quite similar. This arrangement is similar in some respects to that seen in M. pallidum Perkins & Balfour-Browne, 1994, and indeed females of M. sabulosum sp. nov. may key to this species in Perkins & Balfour-Browne (1994) due to the shape of their elytra. Whether these similarities indicate an evolutionary relationship is unclear without genetic data, however.

Distribution. To date known from only two localities on the Bokkeveld Plateau. Both of these are temporary streams, where M. sabulosum sp. nov. was netted from sand and fine gravel with shallow running water. In both localities the species was very abundant, many more specimens being observed than were collected.

Etymology. From the latin sabulum (= coarse sand), in reference to the sandy streams from which this species was collected.

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 6. Habitats on the Bokkeveld Plateau. A – B) Avontuur Reserve, stream below Fynbos Cottage (Site 5); B) C) Oorlogskloof Reserve, Oorlogskloof River below Driefontein Waterfall (Site 11) Photos D. T. Bilton.

FIGURE 7. Habitats on the Bokkeveld Plateau. A) Oorlogskloof Canyon, approach to Papkuilsfontein Waterfall (Site 12); B) Oorlogskloof Canyon, pools in stream above Papkuilsfontein Waterfall (Site 12). Photos D. T. Bilton.

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.