Chasmogenus pandus, 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 pandus sp. nov. Figures 5D-F , 10D , 15A-D , 17

Type material.

Holotype (male): "Suriname: Para District/ Zanderij, near Guesthouse/ 05°27.5'N, 055°13.0'W / 9-18-FEB-2010; P.Skelley,/ W.Warner, C. Gillett; FIT", "[barcode]/SEMC1085915/ KUNHM-ENT", "HOLOTYPE/ CHASMOGENUS/ pandus sp. n./ des. Smith & Short." (NZCS). Paratypes (15): Brazil: Amapa: ca. 1 km E Oiapoque, 3.85039°, -51.81683°, 17 m, 18.vii.2018, leg. Short, flotation of detritus on forested seep, BR18-0718-03C (1 ex., INPA, DNA Voucher SLE1858). French Guiana: Roura, 27.4 km south-southeast, 4°44'20"N, 52°13'25"W, 280 m, 10 JUN 1997, leg. J. Ashe and R. Brooks, Flight Intercept Trap, FG1AB97 177 (2 exs., SEMC); same data as previous except: 23-24 May 1997, FG1AB97 022 (1 ex., SEMC); same data as previous except: 25-29 May 1997, FG1AB97 079 (1 ex., SEMC). Suriname: Para District: same data as holotype (9 exs., SEMC); same data as previous except: 7-9-FEB-2010, lights (1 ex., SEMC).

Differential diagnosis.

The very narrow gap between the clypeus and the labrum (Fig. 10D ) is a characteristic shared only with C. ligulatus , but the two differ in the form of the aedeagus, in which the median lobe of C. pandus is very thin and the parameres are parallel-sided along the outer margins (Fig. 15A-D ), which contrasts with the very convex parameres of 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 3.5-3.7 mm. Body form elongate oval with slightly curved lateral margins. Dorsum of head bicolored, frons dark red-brown, clypeus and labrum slightly paler (Fig. 10D ). Pronotum and elytra uniformly dark brown. Venter uniformly dark brown (Fig. 5F ). Head. Ground punctation on head moderately coarse. Clypeus with medial anteroposterior emargination which exposes a very narrow, wide gap between the clypeus and labrum (Fig. 10D ). Mentum strongly depressed in anteromedial two-thirds with subtriangular notch. Maxillary palps long, longer than width of head immediately anterior to the eyes. Thorax. Ground punctation on pronotum fine. Prosternum tectiform. Mesoventrite with elevation forming a posteromedial longitudinal carina, increasing in elevation anteroposteriorly with highest elevation near protrochanters; slightly convex along outer margins. Metafemora densely pubescent in basal six-sevenths (Fig. 5F ). Aedeagus. Aedeagus (Fig. 15A-D ) 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 long, narrow sliver with a sharply acute apex that extends to the apex of the parameres. Gonopore situated in the middle of the median lobe, ca. two gonopore widths below the apex. Parameres symmetrical, with outer margins strongly bisinuated, giving the margins a weakly undulating appearance, apical half not wider 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 pandus , meaning “bent” after the curved sclerite of the medial lobe of the aedeagus.

Distribution.

Known from Brazil ( Amapá), Suriname (Para District), and French Guiana (Fig. 17 ).

Biology.

Specimens from French Guiana and Suriname were collected via a Flight Intercept Trap. The single specimen from Brazil was collected by floating detritus in a forested seepage.

Remarks.

Most examined specimens appeared to be more translucent than is typical of most species of Chasmogenus . It is unknown if this was due to preservation method or an actual diagnostic feature of this species.

Figures

Figure 5. Habitus of Chasmogenus spp. A-C C. acuminatus: A dorsal view B lateral view C ventral view. D-F C. pandus: D dorsal view E lateral view F ventral view. Scale bar: 2 mm.

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.