Chasmogenus amplius, 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 amplius sp. nov. Figures 2A-C , 9A , 14A , 17 , 20A

Type material.

Holotype (male): "Venezuela: Amazonas State/ 4°58.838'N, 67°44.341'W; 95m/ Communidad Caño Gato, on Rio/ Sipapo; 16.i.2009; leg. Short/ Miller, Camacho, Joly, & García / VZ09-0116-01X: along stream", "[barcode]/ SM0843452/ KUNHM-ENT", "HOLOTYPE/ CHASMOGENUS/ amplius sp. n./ des. Smith & Short" (MIZA). Paratypes (57): Venezuela: Amazonas: Same data as holotype (53 exs., MIZA, SEMC, including DNA voucher SLE1201); stream along Rio Sipapo, 4°55.849'N, 67°44.645'W, 87 m, 16.i.2009, leg. Short, García, Camacho, Miller and Joly, stream habitats, VZ09-0116-02X (2 exs., SEMC); Communidad Caño Gato, 4°58.845'N, 67°44.345'W, 100 m, 7.i.2006, leg. A.E.Z. Short, stream margin/detritus, AS-06-016 (2 exs., SEMC).

Differential diagnosis.

The large size (ca. 5.0 mm) and broad body form (Fig. 2A-C ) of this species serve to differentiate C. amplius from most other congeners, and no other sympatric species may be confused with it. It is approximately the same size as and is morphologically similar to C. berbicensis from eastern Guyana, but may be distinguished by its paler dorsal coloration.

Description.

Size and color. Total body length 4.5-5.0 mm. Body form elongate oval with broad, slightly curved lateral margins. Dorsum of head bicolored, frons dark brown, clypeus and labrum distinctly paler (Fig. 9A ). Pronotum and elytra dark orange-brown to dark brown (Fig. 2A ). Venter dark red-brown centrally, dark brown marginally (Fig. 2C ). Abdominal ventrites orange-brown. Head. Ground punctation on head fine. Clypeus with anteromedial emargination, which exposes a rounded to angulate gap between clypeus and labrum (Fig. 9A ). Mentum strongly depressed on anterior half with subtriangular anteromedial notch. Maxillary palps long, longer than width of head immediately posterior to eyes. Thorax. Ground punctation on pronotum fine. Prosternum weakly tectiform. Mesoventrite with weak elevation forming a posteromedial longitudinal carina. Metafemora densely pubescent in basal nine-tenths (Fig. 2C ). Aedeagus. Aedeagus (Fig. 14A ) with median lobe widest at base and very slightly tapering until the apical quarter, then narrowing abruptly to form an acute triangular apex which is even with or 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 straight, with apex slightly inwardly curved and bluntly rounded. Basal piece long, ca. three-quarters the length of the parameres.

Variation.

There is a fair amount of variation in dorsal coloration; most specimens examined are medium-orange brown, whereas some are slightly paler.

Etymology.

The species name is derived from the Latin amplius , meaning “larger”, after the large body size of this species, the largest known species of the genus in northern South America.

Distribution.

Known from a few closely situated localities along the Orinoco River in southern Venezuela (Amazonas) (Fig. 17 ).

Biology.

This species has been collected in series along the margins of a small sandy stream that flowed into the Rio Sipapo (Fig. 20A ). Specimens were found by agitating marginal areas where leaf detritus and sand had accumulated.

Figures

Figure 2. Habitus of Chasmogenus amplius: A dorsal view B lateral view C ventral view. Scale bar: 2 mm.

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 14. Aedeagi of (dorsal view) of Chasmogenus spp. A C. amplius B C. clavijoi C C. gato D C. berbicensis E C. brownsbergensis F C. schmits G, H C. guianensis G specimen from Suriname H specimen from Guyana. Scale bar: 0.25 mm.

Figure 17. Distribution of Chasmogenus spp.

Figure 20. Habitat of Chasmogenus spp. A Type locality and habitat for C. amplius and C. gato, Venezuela: Amazonas, Cano Gato (collecting event VZ 09 - 0116 - 01 X) B type locality and habitat for C. clavijoi, Venezuela: Guarico, San Nicolasito Field Station (collecting event VZ 09 - 0110 - 02 X) C-F habitat for C. australis: C Venezuela, Barinas, 13 km southeast of Ciudad Bolivia (collecting event VZ 12 - 0125 - 02 A) D Guyana, near Kusad Mountains (collecting event GY 13 - 1027 - 01 A). E, F Brazil, Roraima, near Caracarai, red circles showing live individuals of C. australis floating on the water surface (collecting event BR 18 - 0116 - 05 A).