Chasmogenus ligulatus, 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 ligulatus sp. nov. Figures 10B , 15E , 17 , 21B

Chasmogenus sp. X Short, 2013: 87 (in part).

Type material.

Holotype (male): "Suriname: Sipaliwini District/ 2.97731N, 55.38500W, 200 m/ Camp 4 (low), Kasikasima; sandy/ creek, trail to Kasikasima; leg. A. Short/ 22.iii.2012; SR12-0322-02A/ flotation; 2012 CI-RAP Survey", "[barcode]/ SEMC1086819/ KUNHM-ENT". "HOLOTYPE/ CHASMOGENUS/ ligulatus sp. n./ des. Smith & Short" (NZCS). Paratypes (5): Suriname: Sipaliwini: same data as holotype except: 20.iii.2012, sandy stream on trail to METS camp, SR12-0320-02A (4 exs., SEMC, including DNA Voucher SLE474); same data as holotype except: 20-25.iii.2012, detrital pools along trail to METS camp, SR12-0320-03A (1 ex., SEMC).

Differential diagnosis.

The very thin gap between the clypeus and labrum (Fig. 10B ) distinguish this species from all other congeners except for C. sinnamarensis , both of which are similar in size and morphology, but C. sinnamarensis is translucent dark red in dorsal coloration, and C. ligulatus is opaque and dark brown dorsally.

Description.

Size and color. Total body length 3.2-3.5 mm. Body form elongate oval with slightly curved lateral margins. Dorsum of head multi-colored, frons dark brown, clypeus slightly paler, labrum distinctly paler (Fig. 10C ). Pronotum dark orange-brown, slightly paler marginally. Elytra uniformly dark orange-brown to dark brown. Venter orange-brown mesally, dark brown marginally. Head. Ground punctation on head fine to moderately dense. Clypeus with anteromedial emargination which exposes a shallowly rounded gap between the labrum and the clypeus (Fig. 10C ). Mentum strongly depressed in anterior two-thirds with triangular notch. Maxillary palps long, longer than width of head immediately posterior to eyes. Thorax. Ground punctation on pronotum fine. Prosternum very weakly tectiform. Mesoventrite with weak elevation forming a posteromedial longitudinal carina. Metafemora densely and uniformly pubescent in basal nine-tenths. Aedeagus. Aedeagus (Fig. 15E ) with median lobe nearly parallel-sided but curved slightly to the left; apex bluntly rounded, distinctly extending beyond the apex of the parameres. Sclerite of the median lobe expanded and developed into a long, narrow crescent. Gonopore situated near the base of the median lobe. Parameres symmetrical, with outer margins strongly sinuate; the basal half of the parameres parallel sided with apical half appearing greatly expanded, then tapering to a blunt apex. Basal piece short, ca. one-third the length of the parameres.

Etymology.

The species name is derived from the Latin ligula, meaning “tongue” after the broad and extended tongue-like form of the median lobe of the aedeagus.

Distribution.

Known from lowland rainforest near the base of Mt. Kasikasima in southern Suriname (Fig. 17 ).

Biology.

Two of the three collecting events for this species were from small sandy streams in dense rainforest (Fig. 21B ). A single specimen was also collected from a very large nearby detrital pool that was draining into a stream.

Figures

Figure 10. Dorsal view of heads of Chasmogenus spp. from Suriname and Guyana A C. brownsbergensis B C. ligulatus C C. guianensis D C. pandus.

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 21. Habitat of Chasmogenus spp in Suriname. A Type locality and habitat for C. brownsbergensis, Brownsberg Nature Park (collecting event SR 12 - 0804 - 03 A) B type locality and habitat for C. ligulatus, near Mt. Kasikasima (collecting event SR 12 - 0320 - 02 A) C type locality and habitat for C. tafelbergensis, summit of Tafelberg tepui (collecting event SR 13 - 0817 - 01 A) D type locality and habitat for C. schmits, S of Kwamala along the Kutari River (collecting event SR 10 - 0316 - 01 B) E habitat for C. acuminatus, Central Suriname Nature Reserve, Raleighvallen (collecting event SR 16 - 0316 - 01 B) F habitat for C. guianensis, upper Palumeu River, (collecting event SR 12 - 0311 - 01 A).