Mesoceration rugulosum, 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 : 505-506

Mesoceration rugulosum sp. nov.

( Figs 3 , 4 & 5 )

Type locality. South Africa, Western Cape, Franschhoek Pass, wet rock faces beside stream crossing R45 road, 500 m ( Fig. 5 D).

Type material. Holotype (male): “ 25/ix/2009 South Africa WC// Franschhoekpas, 500 m wet rock//faces beside R45 road// D T Bilton leg.” (genitalia extracted and mounted on same card) and red holotype label ( SAM).

Paratypes (18) 7 ♂ 11 ♀ “ 25/ix/2010 South Africa WC// Franschhoekpas, 500 m small// stream beside R45 road// D T Bilton leg.” [same locality as Holotype] ( CDTB, MCZ, SAM, SANC, TMSA). All with red paratype labels.

Description. Size: Holotype: BL 1.7 mm; EL 0.95 mm; EW 0.65 mm. Paratypes: ♂s BL 1.75–1.8 mm; EL 0.95–1.0 mm; EW 0.65–0.67 mm. ♀s BL 1.75–1.85 mm; EL 0.95–1.05 mm; EW 0.65–0.7 mm.

Colour: Dorsum ( Fig. 3 A) reddish brown to black. Head black with reddish brown anteocellar furrows, ocelli and vertex. Pronotum dark pitchy brown on disc, broadly reddish brown close to lateral margins, and narrowly so along anterior and posterior margins. Elytra dark reddish brown, pitchy along suture and on carina and along lateral margins. Legs and maxillary palpi reddish brown; maxillary palpi with apical segment infuscated. Venter reddish brown, metaventrites piceous, especially laterally; elytral epipleurs piceous.

Head: Labrum weakly transverse, rounded apicolaterally, with broad apicomedian emargination over approx. 0.5 of length. Sides of apicomedian emargination and anterior angles weakly raised. Surface shining, with obsolete, open microreticulation and scattered punctures. Stout, white, recumbent setae along anterior and lateral margins Frontoclypeal suture weak, arcuate. Clypeus, frons and vertex strongly microreticulate, rugulose, granulate on centre of frons. Anteocellar furrows broad, open laterally, rugulose. Ocelli small, shining. Compound eyes large, occupying approx. 0.4 of lateral margin of head, 16 ommatidia in longest series.

Pronotum: Cordate, slightly transverse, broadest in middle. Anterior margin arcuate over central 0.5, without hyaline border; posterior margin straight. Anterior angles obtusely rounded; posterior angles rectangular. Lateral margins sinuated from widest point to base; broadly marginated and crenulated. Surface dull, rugulose, with strong microreticulation of isodiametric meshes, scattered, flat, shining granules on reliefs, and flattened decumbent yellow setae in anterior and posterior 0.25 of disc. With 10 distinct foveae as follows: Anterior median fovea elongate, broadest in posterior 0.6; posterior median fovea shorter, but also elongate, almost meeting anterior median fovea. Anterior admedian fovea small, shallow, rounded, open laterally; posterior admedian fovea broad, shallow oval, orientated anterolaterally. Anterior and posterior adlateral foveae shallow, rounded, open laterally.

Elytra: Elongate oval, broadest behind middle, subparallel over median 0.6 then attenuated to broad, truncately rounded apices. Posterolateral angles rounded but evident; sutural angles obtuse. Broadly explanate at sides. Punctures of elytral series evident to apex, punctures larger in anterior 0.5, becoming smaller and less impressed behind. Discal series striate impressed. Series 1 and 2 confluent just behind posterior declivity; 5 and 6 confluent over anterior 0.3. Intervals shining, granulate; granules bearing short, decumbent setae. Interval 8 strongly carinate to approx. 0.2 from apex.

Legs: Apical protarsomere with two ventral setae, one longer and stouter than the other; basal three protarsomeres with suction setae.

Venter: Mentum shining, rugulosely microreticulate, with isodiametric meshes. Long, erect, yellow setae along anterior margin. Cardo, basistipes and palpifer with white, erect setae. Submentum shining, with obsolete, transverse microreticulation. Genae shining anteriorly, with obsolete transverse microreticulation centrally, stronger and more isodiametric laterally; with rugulose microreticulation and hydrofuge vestiture posteriorly, vestiture extending along hind margin of ocular ridge behind compound eyes. Gula shining, with transverse microreticulation, stronger posteriorly. Prosternum with well-marked, narrow, shining, glabrous central ridge. Remainder of surface rugulose, with dense hydrofuge vestiture. Pronotal hypomeron broad, shining, with rugulose isodiametric microreticulation and broad, open, oval fovea situated anteriorly to the front margin of procoxae. Mesoventrite and metaventrites with dense hydrofuge vestiture. Mesoventral plaques forming an inverted Y, stem 0.5 length of arms. Weak admedian and adlateral ridges also present, but covered in vestiture. Metaventrite with broadly elongate median fovea over posterior 0.6, and broad, transverse depressions anteriorly, below mesocoxae; small, glabrous semicircular patch present posteromedially. Elytral pseudepipleurs broad, shining, very narrow over posterior 0.25; epipleurs shining, ridge-like to apex. Abdominal ventrites 1–5 with dense hydrofuge vestiture.

Abdominal ventrite 6 shining, glabrous, with obsolete transverse microreticulation and irregular row of elongate, yellow decumbent setae close to posterior margin.

Aedeagus: Elongate, relatively broad in ventral view, with parameres attaching close to base and extending to the apex of the main piece. Main piece with very broad truncate tooth at apex. Distal lobe elongate, curving strongly to the left in ventral view ( Fig. 4 A).

Female: Slightly broader than males, with more strongly explanate elytral margins and truncate apices. Submentum more strongly rugulose than in males. Abdominal ventrite 5 with shining, semicircular glabrous patch over posterior 0.5. Glabrous area divided in half: anterior 0.5 with thicker cuticle, and weakly transverse microreticulation, posterior 0.5 thinner, and devoid of microreticulation; junction between two areas marked by irregular crenulated puncture row, bearing long, yellow, decumbent setae. Abdominal ventrite 6 entirely glabrous, shining, with isodiametric microreticulation and a row of short, stout setae close to posterior margin. Legs simple.

Variation: Paratypes vary slightly in colouration, some appearing slightly darker than the holotype.

Differential diagnosis. A member of the truncatum group sensu Perkins & Balfour-Browne (1994). As with M. brevigranum Perkins & Balfour-Browne, 1994 and M. granulovestum Perkins, 2008 , the pronotal reliefs of M. rugulosum sp. nov. are rugulosely sculptured and granulate. M. granulovestum is readily distinguished from the new species due to its much narrow pronotum, relative to the elytra. M. brevigranum is narrower overall, with deeper pronotal foveae and more evident granules on the reliefs. The new species is also clearly distinguished on its aedeagus, the broad tooth of the main piece being unique so far within the genus.

Distribution. To date known only from the type locality ( Fig. 5 D), a thin film of water flowing over a sloping sandstone rockface beside a stream at Franschhoek Pass.

Etymology. Named in reference to the heavily sculptured head and pronotum.

Figures

FIGURE 3. Habitus of Mesoceration holotypes. A) M. rugulosum sp. nov.; B) M. sewefonteinense sp. nov.; C) M. sinclairi sp. nov.

FIGURE 4. Aedeagi of Mesoceration species. A) M. rugulosum sp. nov., holotype; B) M. sewefonteinense sp. nov., holotype; C) M. sinclairi sp. nov., holotype; D) M. littlekarroo, Swartberg, permanent stream below Kangoberg on Gamkaskloof road. Scale bar = 0.25 mm

FIGURE 5. Habitats of Mesoceration species in South Africa. A) KwaZulu-Natal, uKhahlamba Drakensberg National Park, Injisuthi, stream in Afromontane forest remnant below Van Heyningen’s Pass— M. caniplenum sp. nov., beetles collected from the wet rockface on the right hand side of the stream; B) Western Cape, Matsikammaberg, stream 1 km NW of Sewefontein farm— M. foggoi sp. nov., M. umbrosum; C) Western Cape, Cederberg, Breëwaterkloof stream, ca. 2 km SE of Uitkyk Pass, 1,050 m— M. hirsutum sp. nov., M. dissonum, M. granulovestum, M. jucundum, M. languidum, M. periscopum, M. piceum, M. repandum, M. rivulare; D) Western Cape, Franschhoek Pass, wet rock faces beside stream crossing R 45 road, 500 m— M. rugulosum sp. nov. Photos D. T. Bilton.