Mesoceration helmei, Bilton, David T., 2015

Bilton, David T., 2015, New species and new records of Mesoceration Janssens, 1967 from South Africa (Coleoptera, Hydraenidae), Zootaxa 3972 (4), pp. 495-520 : 501-503

Mesoceration helmei sp. nov.

( Figs 1 & 2 )

Type locality. South Africa, Western Cape, Groote Winterhoek mountains, small stream below Sneeugatpiek, 1,300 m.

Type material. Holotype (male): “ 11/ii/2015 South Africa WC// Groote-Winterhoekberge stream below// Sneeugatpiek 1,300 m D T Bilton leg.” (genitalia extracted and mounted on same card) and red holotype label ( SAM).

Paratypes (14) 4 ♂ 10 ♀ same data as holotype ( CDTB, MCZ, NMW, OUMNH, SAM, SANC, TMSA). All with red paratype labels.

Description. Size: Holotype: BL 1.55 mm; EL 0.9 mm; EW 0.6 mm. Paratypes: ♂s BL 1.55–1.7 mm; EL 0.9– 1.0 mm; EW 0.6–0.65 mm. ♀s BL 1.55–1.7 mm; EL 0.9–1.0 mm; EW 0.6–0.65 mm.

Colour: dorsum ( Fig. 1 C) dark piceous brown to black, lateral margins of elytra and ocelli paler. Legs and maxillary palpi yellow; last segment of maxillary palpi infuscated in apical 0.6. Venter dark piceous brown to black, with silvery hydrofuge vestiture on much of thorax and abdomen. Head somewhat paler, mentum, basistipes and palpifer yellowish-red.

Head: Labrum slightly transverse, rounded apicolaterally, with apicomedian emargination running approx. 0.5 of length. Sides of apicomedian emargination and anterior angles weakly raised. Surface weakly shining, with shallow, isodiametric to elongate microreticulation and scattered, decumbent setae, especially towards posterior margin. Frontoclypeal suture well-marked, almost linear. Entire upper surface of head dull, with strong rugulose microreticulation; meshes larger on clypeus and lateral areas of frons, smaller on central frons and vertex. Anteocellar sulci shallow, open anteriorly. Ocelli small, shining. Compound eyes relatively small, occupying 0.4 lateral margin of head, 10 ommatidia in longest series.

Pronotum: Cordate, slightly transverse, broadest just in front of middle. Anterior margin arcuate over median 0.5, without hyaline border; posterior margin bisinuate around centre. Anterior angles obtusely rounded; posterior angles rectangular. Lateral margins sinuated from widest point to base; broadly marginated and moderately serrate. Surface dull, with rugulose microreticulation and shallow scattered medium punctures which are almost obscured by the microsculpture. Meshes of microreticulation similar in size to central frons. Irregular row of large punctures close to anterior and posterior margins. With 10 distinct foveae as follows: Anterior median fovea elongate; posterior median fovea elongate oval; both deepest in centre. Anterior admedian fovea shallow, oval; posterior admedian fovea shallow, elongate oval, orientated anterolaterally. Anterior and posterior adlateral foveae deep, pitlike; anterior smaller and shallower than posterior.

Elytra: Elongate oval, broadest at middle. Subparallel over anterior 0.5, then attenuated to truncately rounded apices. Sides narrowly explanate, especially anteriorly, entire. Punctures of elytral series relatively coarse; larger in anterior 0.5, smaller and shallower posteriorly. Discal series very weakly striate impressed in anterior 0.6. Serial punctures with fine decumbent setae arising from granules on anterior puncture margin, not usually reaching next puncture in row. Series 1 and 2 confluent at posterior declivity, and becoming closely subparallel in basal 0.3. Series 5 and 6 confluent at middle. Intervals granulate, granules bearing short decumbent setae in anterior 0.25.

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

Wings: Reduced.

Venter: Mentum shining, depressed in middle, with strong elongate to isodiametric microreticulation. Long suberect golden setae along anterior margin and scattered punctures in posterior 0.5, with short, stout, recumbent setae. Submentum shining, with shallow transverse microreticulation, especially evident posteriorly. Genae shining, with transverse wrinkles centrally, and transverse microreticulation meshes laterally. Gula shining with fine transverse microreticulation. Prosternum with distinct central ridge; entire surface rugulose, with dense hydrofuge vestiture. Pronotal hypomeron broad, smooth and shining, lacking microreticulation; shallow, round fovea close to inner anterolateral angle. Mesoventrite and metaventrite with dense hydrofuge vestiture. Mesoventral plaques glabrous, forming an inverted Y; admedian and adlateral ridges also present but covered in vestiture. Metaventrite with elongate median fovea over posterior 0.5; weak median ridge present anterior to furrow and paired, shallow, rounded admedian foveae anteriorly, below mesocoxae. Elytral pseudepipleurs broad, shining with traces of transverse wrinkles, narrowing to apex over posterior 0.5; epipleurs narrow, ridge-like, shining except for small patch of hydrofuge vestiture at level of mesocoxae. Abdominal ventrites 1–4 with hydrofuge vestiture; denser laterally and sparser centrally. Abdominal ventrite 5 with large semicircular shining glabrous patch, occupying 0.1 of length of ventrite laterally, 0.5 centrally; devoid of microreticulation. Irregular transverse row of medium punctures bearing decumbent setae 0.3 from apex. Abdominal ventrite 6 glabrous, shining, with weak transverse microreticulation and transverse row of medium punctures bearing decumbent setae 0.25 from apex.

Aedeagus: Elongate, straight in ventral view, with parameres attaching close to base and extending well beyond the apex of the main piece. Main piece with narrow, bluntly pointed apical tooth on left side, partly overhanging base of distal lobe. Distal lobe elongate, arcuate, extending beyond the apices of the parameres ( Fig. 2 C).

Female: Slightly broader than male, especially on elytra, which have more broadly explanate lateral margins. Elytral apex produced, acuminate, with narrow, truncately rounded apices. Abdominal ventrite 5 with broad, shining, concave glabrous patch over central 0.75, running from approx. 0.1 behind anterior margin. Impunctate and lacking microreticulation; posterior margin thickened and rounded, with long golden decumbent setae following curvature of hind margin.

Variation: Paratypes vary in size, but are otherwise relatively uniform in structure. Some covered in flocculated deposits.

Differential diagnosis. A member of the endroedyi group sensu Perkins & Balfour-Browne (1994). M. helmei sp. nov. would key to M. concessum Perkins & Balfour-Browne, 1994 in this work, on the basis of the weak granules of the elytral intervals and the first and second elytral series being confluent at the posterior declivity. The new species differs from both this species and M. tabulare Perkins, 2008 in the relatively broader habitus, especially on the elytra, which are less elongate, more strongly curved towards the apices, and have a lower carina on the 8th interval. M. helmei sp. nov. also has much less evident pronotal punctation, and shinier elytral intervals, as well as very different male genitalia.

Distribution. To date known only from the type locality, a small cold stream in a shaded gulley below Sneeugatpiek in the Groote Winterhoek mountains north of Tulbagh; an area with frequent and relatively extensive winter snows. The beetles were found in a small spring pool below a cliff beside a permanent stream section, where they were abundant together with Rapnus sp. ( Dryopidae ). Mesoceration apicalum Perkins & Balfour-Browne, 1994 was abundant in the nearby stream itself.

Etymology. Named after the South African botanist Nick Helme, who has provided me with numerous valuable suggestions on areas to sample in the Cape, and was present when the type series was collected.

Figures

FIGURE 1. Habitus of Mesoceration holotypes. A) M. caniplenum sp. nov.; B) M. foggoi sp. nov.; C) M. helmei sp. nov.; D) M. hirsutum sp. nov.

FIGURE 2. Aedeagi of Mesoceration species. A) M. caniplenum sp. nov., holotype; B) M. foggoi sp. nov., holotype; C) M. helmei sp. nov., holotype; D) M. hirsutum sp. nov., paratype. Scale bar = 0.25 mm.