Chasmogenus clinatus, Glynn & Short, 2021

Glynn, Rachel D. & Short, Andrew Edward Z., 2021, New species and records of Chasmogenus Sharp, 1882 from the southwestern margin of the Guiana Shield (Coleoptera: Hydrophilidae: Acidocerinae), Zootaxa 5048 (3), pp. 435-443 : 436-440

Chasmogenus clinatus sp. n.

Figures 2A–B , 3A , 4A–D , 6

Type Material. Holotype (male): “BRAZIL: Amazonas : Manaus / -2.93079, -59.97514, 75m / Ducke Reserve , Igarape Barro / Branco; Short & team; forest/ pools; 6.vi.2018; BR18-0606-02C”, “[barcode]/ SEMC1623338 / KUNHM-ENT” ( INPA) . Paratypes (34): BRAZIL: Amazonas: Same data as holotype (8 exs., INPA, SEMC, including DNA Voucher is SLE1848) ; same data but “forest pools”, BR18-0606-02A (4 exs., SEMC) ; same data but stream margin and associated backwater swampy area, 9–10.vi.2018, BR18-0609-3A (2 exs., SEMC) . VENEZUELA: Amazonas: Cerro de la Neblina , 1 km S. Basecamp, 17.ii.1985, leg. Faitoute & Steiner, “along small whitewater stream, pools of dead leaves and sticks” (20 exs., USNM, MIZA, SEMC) .

Differential diagnosis. Chasmogenus clinatus is very similar to a cluster of species that have sinuate parameres and a well-developed accessory sclerite on the median lobe ( Fig. 4A–D ). The aedeagus of this species is most similar to that of C. pandus ( Fig. 4F ) in that both have a bent medial sclerite that lies dorsally to the median lobe and the outer margins of the parameres have a weak undulating appearance. However, the median lobe of C. clinatus is uniformly wide throughout its length until the apex acuminates past the parameres, whereas the median lobe of C. pandus is wider at the base and gradually acuminates throughout the entire length towards the apex. The outer margins of the parameres of C. clinatus have a single medial constriction (sinuate) between the base and the position of the gonopore and C. pandus has two lateral constrictions (bisinuate), one medial and one closer to the apex of the parameres. The two species may be differentiated by dorsal coloration as well: C. clinatus is dark brown, whereas C. pandus is a slightly paler reddish brown.

Description. Size and color. Total body length 2.9–3.6 mm. Body form elongate oval with slightly curved lateral margins. Dorsum of head orange-brown to very dark brown, clypeus and labrum paler brown ( Fig. 3A ). Pronotum and elytra uniformly dark orange-brown ( Fig. 2A ). Venter uniformly dark orange-brown ( Fig. 2B ). Head. Ground punctation on head fine. Clypeus with anteromedial emargination, which exposes a narrow, rounded to angulate gap between the clypeus and labrum ( Fig. 3A ). Mentum deeply depressed in anterior two-thirds with a triangular to rounded anteromedial notch. Maxillary palps long, longer than width of head immediately posterior to eyes. Thorax. Ground punctation on pronotum fine ( Fig. 2A ). Prosternum very weakly to not at all tectiform. Mesoventrite with moderate elevation forming a thin posteromedial longitudinal carina. Metafemora densely pubescent in basal nine-tenths ( Fig. 2B ). Aedeagus. Aedeagus ( Fig. 4A–D ) with median lobe nearly parallel-sided and uniformly wide, then tapering gradually to a weakly acuminate apex, distinctly extending beyond the apex of the parameres. Sclerite of the median lobe expanded and developed into a long, narrow sliver, angled slightly to the left with a sharply acute apex that extends to or just beyond the apex of the parameres. Gonopore situated in the middle of the median lobe, ca. two to three gonopore widths below the apex. Parameres symmetrical, outer margins with a single medial constriction, apical half slightly narrower than basal half; apex slightly acuminate. Basal piece short, ca. one-third the length of the parameres.

Etymology. The species name is derived from the Latin clinatus meaning “bent” or “sloped” after the condition of the medial sclerite on the median lobe of the aedeagus.

Distribution. This species is known from the Ducke Reserve in Manaus, state of Amazonas, Brazil and from the extreme south of Venezuela at the foot of Cerro de la Neblina.

Biology. This species was collected from a series of forest pools and riparian areas in northern Brazil (Amazonas) and along whitewater streams in southern Venezuela.

Figures

FIGURE 2: Dorsal and ventral habitus of Chasmogenus spp. A–B C. clinatus sp. n. C–D C. gironae sp. n.

FIGURE 3: Dorsal view of heads of Chasmogenus spp. A C. clinatus sp. n. B C. gironae sp. n. C C. inpa sp. n.

FIGURE 4: Aedeagi of Chasmogenus spp. A–D C. clinatus sp. n. A specimen from Brazil (Amazonas) B specimen from Venezuela C specimen from Brazil (Amazonas) D specimen from Brazil (Amazonas) E C. ligulatus, F C. pandus, G C. acuminatus (Suriname), H C. acuminatus (Brazil: Pará). Scale bar: 0.20 mm

FIGURE 6: Distribution of new Chasmogenus spp.