Chasmogenus flavomarginatus, 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 flavomarginatus sp. nov. Figures 3A-C , 8E , 12B, C , 17 , 19D

Type material.

Holotype (male): "Venezuela: Barinas State/ 8°48.424'N, 70°31.139'W, 992m/ ca. 13km NW Baranitas, 24.i.2012/ leg. Short, Arias, & Gustafson/ Small stream pool: VZ12-0124-02B", "[barcode]/ SEMC1030004/ KUNHM-ENT", "HOLOTYPE/ CHASMOGENUS/ flavomarginatus sp. n./ des. Smith & Short" (MIZA). Paratypes (88): Venezuela: Barinas: Same data as holotype (85 exs., MIZA, SEMC, including DNA voucher SLE1235); same data as holotype except: seepage by road, VZ12-0124-02A (2 exs., SEMC, including DNA voucher SLE1083). Táchira: near El Tama, 26.i.2012, leg. Short, VZ12-0126-04A (1 ex., SEMC, DNA voucher SLE1084).

Differential diagnosis.

The lack of a clypeal emargination (Fig. 8E ) easily separates C. flavomarginatus from most other congeners. It shares this characteristic with C. lineatus but can be separated by the overall paler dorsal coloration and the distinct yellow margins (Fig. 3A, B ) of the pronotum (dorsum entirely dark brown to black in C. lineatus ).

Description.

Size and color. Total body length 3.2-3.5 mm. Body form elongate oval with slightly subparallel lateral margins. Dorsum of head very dark brown to black with slightly paler preocular patches (Fig. 8E ). Anterior margin of labrum and lateral margins of clypeus sometimes slightly paler. Pronotum dark brown to black centrally, distinctly bright yellow at anterior and lateral margins (Fig. 3A-B ). Elytra dark red-brown to dark brown, slightly paler or bright yellow marginally (Fig. 3A ). Venter dark red brown, abdominal ventrites dark brown. Head. Ground punctation on head fine. Clypeus and labrum contiguous (Fig. 8E ). Mentum weakly depressed in anterior half with shallowly rounded anteromedial notch. Maxillary palps short, just slightly shorter than width of head immediately posterior to eyes. Thorax. Ground punctation on pronotum fine. Prosternum moderately tectiform. Mesoventrite with elevation forming a posteromedial longitudinal carina with convex distolateral margins. Metafemora densely pubescent in basal four-fifths (Fig. 3C ). Aedeagus. Aedeagus (Fig. 12B, C ) with outer margins of median lobe straight and parallel sided, with apex in the form of an acutely pointed triangle, which slightly extends beyond the apex of the parameres. Sclerite of the median lobe not expanded. Gonopore situated less than half of one gonopore width below the apex of the median lobe. Parameres symmetrical, with outer margins slightly curved along basal four fifths, appearing weakly convex, then curved slightly outward at apex; apex very weakly bifid, with outer lobe more elevated than inner lobe; inner lobe minute, almost appearing absent. Basal piece long, ca. four-fifths the length of the parameres.

Variation.

In material examined, there was some variation in dorsal coloration, ranging from dark brown to black. There is also variation in the coloration of the dorsum of the head, where some specimens had paler margins on the anterior portion of the labrum and the lateral margins of the clypeus, most were uniformly black.

Etymology.

The species name is derived from the Latin flavus, meaning “yellow”, after the distinct yellow margins of the pronotum and elytra.

Distribution.

Known from the Andean States of Táchira and Barinas (Fig. 17 ).

Biology.

A long series of this species was collected in a small pool that was formed by a road-cut in the Andes (Fig. 19D ). It was being fed by a small stream/seepage, in which two additional specimens were collected. The specimen from Táchira was found in a small pool along a dirt road.

Figures

Figure 3. Habitus of Chasmogenus spp. A-C C. flavomarginatus: A dorsal view B lateral view C ventral view. D-F C. bariorum: D dorsal view E lateral view F ventral view. G-I C. castaneus G dorsal view H lateral view I ventral view. Scale bar: 2 mm.

Figure 8. Dorsal view of heads of Chasmogenus spp. A C. castaneus B C. australis C C. bariorum D C. cuspifer E C. flavomarginatus F C. lineatus.

Figure 12. Aedeagi (dorsal view) of Chasmogenus spp. A C. castaneus B C. flavomarginatus C C. flavomarginatus D C. cuspifer E-I C. lineatus. Scale bar: 0.25 mm.

Figure 17. Distribution of Chasmogenus spp.

Figure 19. Habitat of Chasmogenus spp in the Andean region of Venezuela. A, B Type locality and habitat for C. bariorum, C. cuspifer, and C. castaneus, near El Tukuko, Rio Manantial collecting event VZ 09 - 0129 - 01 A) C habitat for C. bariorum and C. cuspifer, Henri Pittier National Park, Rio Cumboto (collecting event VZ 09 - 0104 - 02 B) D type locality and habitat for C. flavomarginatus, ca. 13 km NW of Baranitas (collecting event VZ 12 - 0124 - 02 B) E habitat for C. bariorum and C. lineatus, between San Juan and Dos Caminos, Rio San Antonio (collecting event VZ 09 - 0108 - 02 A) F habitat for C. bariorum and C. lineatus, near Arenales, Rio Salado (collecting event VZ 09 - 0122 - 01 X).