Riberazantaena latissima, Bilton, 2021

Bilton, David T., 2021, Riberazantaena, a new hydraenid genus from the Eastern Arc Mountains of Tanzania (Coleoptera, Hydraenidae), Zootaxa 4999 (6), pp. 573-581 : 578-580

Riberazantaena latissima sp. nov.

( Figs. 1B , 2D & 4 )

Type locality. Tanzania, South Pare Mountains , Chome Forest, S4.27145° E37.92347°, 2072 m .

Type material. Holotype (male): “ TANZANIA South Pare // Mts., Chome For.,// S4.27145° E37.92347° // 2072m, 4.1.2013, sift 40,// V. Grebennikov leg.” and red holotype label ( NMW).

Paratypes (39): 11♂, 28♀ same data as holotype and red paratype labels (2♂, 2♀ in 96% ethanol, remainder dry mounted) ( AMG, CNC, CBP, NMW) .

Description. Size: Holotype: BL 1.80 mm; EL 1.10 mm; EW 0.90 mm. Paratypes: Males BL 1.75–1.80 mm; EL 1.05–1.10 mm; EW 0.85–0.90 mm. Females BL 1.80–1.95 mm; EL 1.15–1.20 mm; EW 0.95–1.00 mm.

Colour: Dorsum ( Fig. 1B ) chestnut brown; pronotal disc and much of head dark brown. Antennae and maxillary palpi yellow, legs yellowish brown. Venter reddish brown; much of head, pronotal hypomeron and elytral epipleura paler.

Head: Labrum strongly transverse, broadly rounded laterally and apically; apical margin slightly raised, with broad, v-shaped apicomedian emargination and long, yellow, comb-like setae at apicolateral angles, particularly in centre; sides and apex minutely serrate. Surface of labrum dull, weakly microreticulate; with sparse, fine punctures, bearing white, recumbent or decumbent setae. Frontoclypeal suture very distinct, arcuate. Clypeus, frons and vertex somewhat dull. Clypeus with strong, open microreticulation of irregular meshes; sparse medium punctures bearing fine, white, recumbent setae. Frons and vertex largely smooth, microreticulation largely effaced, distinct meshes restricted to internal borders of eyes and medially, meshes isodiametric; with sparse, medium to coarse punctures bearing long, white, recumbent setae. Ocelli distinct, shining, each located at the base of short, oblique interocular fovea. Compound eyes moderately large, eight ommatidia in longest series.

Pronotum: Transverse, widest just before middle, then subparallel to posterior angles. Anterior margin broadly but very shallowly arcuate over median 0.3, here with distinct hyaline border; posterior margin weakly bisinuate around centre; lateral margins straight behind widest point, anteriorly arcuate to anterior angles; in lateral view appearing thickened, with upper and lower rim. Anterior angles broadly rounded, posterior angles weakly obtuseangulate. Anterior and posterior impressions very shallow, almost obsolete, U-shaped. Very shallow wide impression at each posterior angle. Surface weakly shining, especially on disc; microreticulation reduced to a few scattered, weak lines. Entire surface punctate, each puncture with anterior margin extended posteriorly as narrow ridge, apparently dividing puncture into a pair of two smaller punctures; long, fine, recumbent setae arising from posterior extreme of dividing ridge. Punctures larger in anterior and posterior impressions and laterally, smaller on disc. Sculpture subrugose anterolaterally.

Elytra: Broad, elongate, attenuate posteriorly. Sides arcuate, explanate margins wide, distinct from shoulder for ca. 0.7 of length; apices separately rounded. Ten-seriate punctate, series on disc moderately striate-impressed, gradually weaker laterally and apically; punctures moderate, round, shallow; each bearing small, fine, white, recumbent or decumbent seta. Interstices weakly shining, each with unilinear row of fine, granulate punctures, bearing long, fine, slightly overlapping recumbent setae, longer and more distinct than setae of puncture rows.

Venter: Mentum, submentum, and genae shining, microreticulation absent; with sparse, fine punctures, bearing fine, white decumbent setae. Gula with sparse medium punctures bearing long recumbent setae; surface between punctures with transverse wrinkles, overall appearance dull. Prosternum rugosely microreticulate and punctate, punctures bearing erect to recumbent setae; mesoventrite same. Pronotal hypomeron broad, glabrous, with weak, isodiametric to elongate microreticulation. Elytral epipleura very broad anteriorly, narrowing over posterior 0.6 and absent at acuminate apices; surface shining, glaborus, without evident microreticulation. Metaventrite dull, with isodiametric to slightly transverse microreticulation; with dense, fine punctures bearing shaggy hydrofuge vestiture; with deep oval impression posteriorly and strong, shining midlongitudinal carina anteriorly; carina and impression confluent. Abdominal ventrites 1–4 completely hydrofuge pubescent; ventrite 5 with row of pubescence at anterior margin only; ventrites 5 and 6 with irregular transverse rows of punctures bearing long, yellowish, decumbent setae close to posterior margin. All ventrites microreticulate, meshes isodiametric to slightly transverse. Last ventrite very sparsely pubescent, free margin markedly arcuate; last tergite with tuft of setae on each side of narrow, shallow apicomedial notch.

Wings: The two specimens examined are micropterous.

Aedeagus: Elongate ( Fig 2D ), main piece weakly arcuate in lateral view; apex broadly truncated in ventral view. Flagellum thin and flexible over most of length, thicker and more heavily pigmented basally, longer than main piece. Note that flagellum is flexible, so detail of curvature is not diagnostic.

Differential diagnosis. Distinguished from R. grebennikovi by the larger size (1.75–1.95 vs. 1.7–1.75 mm), the broader, flatter habitus ( Fig. 1 ), the more strongly impressed elytral series and differences in the aedeagus, particularly the apex of the main piece ( Fig. 2C vs. D).

Etymology. From the Latin latissimus – broadest – in recognition of the very broad, flat habitus of this species.

Distribution. Currently known only from forest litter in the Chome Forest ( Fig. 4A ), South Pare Mountains in northern Tanzania ( Fig. 4B ).

Figures

FIGURE 1. Habitus images of A) Riberazantaena grebennikovi, Uluguru Mountains, Tanzania; B) Riberazantaena latissima sp. nov., Chome Forest, South Pare Mountains, Tanzania. Scale bar = 1 mm.

FIGURE 2. Aedeagi of A) Protozantaena labrata, modified from Perkins (2009); B) Protozantaena palpalis, modified from Perkins (2009); C) Riberazantaena grebennikovi, Uluguru Mountains, Tanzania; D) Riberazantaena latissima sp. nov., Chome Forest, South Pare Mountains, Tanzania. Scale bar = 0.1 mm. Note that the flagella of P. labrata and Riberazantaena spp. are flexible, meaning that curvature etc. is not diagnostic.

FIGURE 4. A) Chome Forest, South Pare Mountains, Tanzania, type locality of Riberazantaena latissima sp. nov. Photo Vasily Grebennikov; B) Map of East Africa showing known localities of Riberazantaena species. Red symbol = R. grebennikovi; blue symbol = R. latissima sp. nov.