Chasmogenus undulatus, Smith & Short, 2020

Smith, Rachel R. & Short, Andrew Edward Z., 2020, Review of the genus Chasmogenus Sharp, 1882 of northeastern South America with an emphasis on Venezuela, Suriname, and Guyana (Coleoptera, Hydrophilidae, Acidocerinae), ZooKeys 934, pp. 25-79 : 25

Chasmogenus undulatus sp. nov. Figures 9E , 15G , 17 , 22B

Chasmogenus sp. A Short, Salisbury, & La Cruz 2018: 193.

Type material.

Holotype (male): "Guyana: Region XIII/ 5°18.261'N, 59°50.257'W; 687 m/ Ayanganna Airstrip, trail from air-/ strip to Ayanganna; forested/ detrital pools; leg. A. Short/ 18.iii.2014/ GY14-0318-01B", "[barcode]/SEMC1313817/ KUNHM-ENT", "HOLOTYPE/ CHASMOGENUS/ undulatus sp. n./ des. Smith & Short" (CBDG). Paratypes (20): GUYANA: Region 8: same data as holotype (4 exs., SEMC including DNA Voucher SLE1618); same data as holotype except: 17.iii.2014, forest detrital pools, GY14-0317-01A (14 exs., CBDG, SEMC including DNA Vouchers SLE1832 and SLE1833); same data as holotype except: 19.iii.2014, trail from airstrip to marshy mined area, GY14-0319-02A (1 ex., SEMC); Ayanganna Airstrip, trail from Blackwater Creek Camp to Potaro River, 5°17.823'N, 59°50.000'W, 684 m, 19.iii.2014, leg. A. Short, forest detrital pools, GY14-0319-01A (1 ex., SEMC, DNA Voucher SLE1831).

Differential diagnosis.

Among species that have a broad clypeal emargination and the apex of the median lobe extending past the apex of the paramere, C. undulatus may be distinguished from the widespread and similar C. acuminatus by the distinctly sinuated outer margins of the parameres (Fig. 15G ) (straight in C. acuminatus ). In other species with sinuated outer margins of the parameres ( C. ligulatus and C. pandus ), this species may be distinguished by the gradually tapered and blunt apex of the median lobe (more pointed in C. pandus , not tapered in C ligulatus ). Examination of the aedeagus is the only way to definitively identify this species. Unassociated females may not be determined with certainty.

Description.

Size and color. Total body length 3.8-4.0 mm. Body form elongate oval with slightly curved lateral margins. Dorsum of head dark brown, clypeus slightly paler (Fig. 9E ). Pronotum dark orange-brown, distinctly paler marginally. Elytra uniformly dark brown. Venter dark red brown to dark brown. Head. Ground punctation on head fine to moderately coarse. Clypeus with anteromedial emargination, which exposes a trapezoidal gap between the clypeus and labrum (Fig. 9E ). Mentum strongly depressed in anterior half with subtriangular anteromedial notch. Maxillary palps long, longer than width of head immediately posterior to eyes. Thorax. Ground punctation on pronotum moderately coarse. Prosternum tectiform. Mesoventrite with elevation forming a posteromedial longitudinal carina with the lateral margins convex. Metafemora densely pubescent in basal six-sevenths. Aedeagus. Aedeagus (Fig. 15G ) with median lobe nearly parallel-sided and widest in basal half, then angled slightly to the left and 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 wide angulate sliver with a sharply acute apex that extends to the apex of the parameres. Gonopore situated ca. 1.5 gonopore widths below the apex of the median lobe. Parameres symmetrical, with outer margins strongly bisinuated, giving the margins a weakly undulating appearance, apical distinctly narrower than basal half; apex bluntly rounded. Basal piece short, ca. one-third the length of the parameres.

Etymology.

The species name is derived from the Latin undulatus , meaning “wavy”, after the curvy and sinuated margins of the parameres.

Distribution.

This species is known from several collections near Mount Ayanganna in western Guyana.

Biology.

Series of this species were collected in forested detrital pools (Fig. 22B ).

Figures

Figure 9. Dorsal view of heads of Chasmogenus spp. A C. amplius B C. acuminatus C C. berbicensis D C. clavijoi E C. undulatus F C. gato.

Figure 15. Aedeagi of Chasmogenus spp. A-D C. pandus A dorsal view (Suriname) B side view (Suriname) C specimen from French Guiana D specimen from Brazil E C. ligulatus F C. sinnamarensis G C. undulatus H, I C. acuminatus H specimen from Suriname I specimen from Guyana. Scale bars: 0.25 mm.

Figure 17. Distribution of Chasmogenus spp.

Figure 22. Habitat of Chasmogenus spp in Guyana. A Type locality and habitat for C. berbicensis, Guyana, margin / detrital sandbar of the upper Berbice River (collecting event GY 14 - 0922 - 02 A) B type locality and habitat for C. undulatus Guyana, near Ayanganna airstrip (collecting event GY 14 - 0317 - 01 A) C habitat for C. acuminatus and C. guianensis, Guyana, small tributary of the upper Berbice River (collecting event GY 14 - 0924 - 01 A) D habitat for C. acuminatus (collecting event GY 13 - 1103 - 02 A).