Chasmogenus lineatus, 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 lineatus sp. nov. Figures 4A-C , 8F , 12E-I , 17 , 19E, F

Type material.

Holotype (male): "Venezuela: Guárico State/ 9°46.320'N, 67°21.177'W, 280m/ Río San Antonio, N. Dos Caminos/ 8.i.2009; leg. Short, Miller & García / VZ09-0108-02A: river margins", "[barcode]/ SEMC0864029/ KUNHM-ENT", "HOLOTYPE/ CHASMOGENUS/ lineatus sp. n./ des. Smith & Short" (MIZA). Paratypes (247): Venezuela: Barinas: River near Bum Bum, 8°18.033'N, 70°45.201'W, 216 m, 15.vii.2009, leg. A. Short et al., river margins, VZ09-0715-02A (48 exs., MIZA, SEMC, including DNA voucher SLE 1772). Guárico: Same data as holotype (35 exs., SEMC); same data as holotype except: leg. Miller & Short, side stream, VZ09-0108-02B (3 exs., SEMC, including DNA voucher SLE1614); Río Guárico, north of San Juan, 9.95788N, 67.37773W, 435 m, 8.i.2009, leg, K. Miller and L. Joly, along river, VZ09-0108-01X (11 exs, SEMC); ~20 km north of Dos Caminos, 9°44.034'N, 67°19.00'W, 225 m, leg. A. E. Z. Short, gravelly margin of river, AS-06-020 (54 exs, SEMC); ~15 km south of San Juan, 9°46.321'N, 67°21.201'W, 255 m, 3.i.2006, leg. A. E. Z. Short, stream margin & rock pools, AS-06-005 (17 exs., SEMC). Lara: Rio Salado, west of Arenales, 10°9.260'N, 69°57.458'W, 490 m, 22.i.2009, leg. Short, García, and Camacho, gravel stream, VZ09-0122-01X (66 exs., MIZA, SEMC, including DNA voucher SLE1061). Portuguesa: Tributary of Rio Guanare, south of Biscucuy, 9°14.457'N, 69°55.994'W, 370 m, 19.i.2009, leg. Short, García, and Camacho, gravel stream, VZ09-0119-03X (8 exs., SEMC); Rio Guanare, north of Guanare, 8°25.773'N, 69°35.202'W, 185 m, 19.i.2009, leg. Short, García, and Camacho, main river, VZ09-0119-02A (4 exs., SEMC); Rio Are at Aparicion, 9°22.900'N, 69°23.153'W, 220 m, 22.i.2012, leg. Short & Arias, river margins, VZ12-0122-02A (1 ex., SEMC).

Differential diagnosis.

The lack of a clypeal emargination serves to distinguish C. lineatus from all other congeners except C. flavomarginatus , from which it may be separated by the almost completely black dorsal coloration of the head (Fig. 8F ) and the absence of pale preocular patches (pale margins and preocular patches present in C. flavomarginatus ).

Description.

Size and color. Total body length 2.9-3.3 mm. Body form very elongate oval with straight, subparallel lateral margins. Dorsum of head very dark brown to black (Fig. 8F ). Pronotum and elytra uniformly dark brown. Prosternum dark orange to dark brown. Mesoventrite uniformly dark orange to dark brown. Metaventrite dark brown, slightly paler on posterior margin. Trochanters and glabrous portion of femora red-orange. Abdominal ventrites dark brown, slightly paler mesally (Fig. 4C ). Head. Ground punctation on head fine. Clypeus and labrum contiguous (Fig. 8F ). Mentum very weakly depressed in anterior half with triangular notch, followed by a medial elevated curved ridge situated posterior to triangular notch. Maxillary palps long, longer than width of head immediately posterior to eyes. Thorax. Ground punctation on pronotum fine. Prosternum moderately tectiform. Mesoventrite with weak elevation forming a posteromedial longitudinal carina with its distolateral margins slightly convex. Metafemora densely pubescent in basal three-fourths (Fig. 4F ). Aedeagus. Aedeagus (Fig. 12E-I ) with median lobe subtriangular in shape, widest at base and gradually tapering along entire length; apex acute, which extends slightly beyond the apex of the parameres. Sclerite of the median lobe not expanded. Gonopore situated slightly more than two gonopore widths below the apex of the median lobe. Parameres symmetrical, with outer margins slightly curved, appearing weakly convex in basal three-quarters, then abruptly angled outwards; apex bifid, appearing "mitten shaped", with outer lobe very large, rounded, and directed outwards, and inner lobe very small and slightly more acuminate. Basal piece long, ca. as long as the length of the parameres.

Variation.

In some specimens examined, the abdominal ventrites were somewhat more densely pubescent than described in the taxonomic treatment. The color of the abdominal ventrites is also slightly variable; in some specimens either the anterior or posterior margin of each ventrite is slightly paler.

Etymology.

The species name is derived from the Latin lineatus , meaning “linear”, after the straight parallel-sided body form and also for the linear, unemarginated anterior margin of the clypeus.

Distribution.

This species is known from lowland gravel streams in the Andean region of Venezuela (Fig. 17 ).

Biology.

This species can be found in abundance in gravel streams along the foothills of the Merida Andes, especially exposed areas of gravel and sand with algae (Fig. 19E, F ).

Figures

Figure 4. Habitus of Chasmogenus spp. A-C C. lineatus: A dorsal view B lateral view C ventral view. D-F C. australis: D dorsal view E lateral view F 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).