Chasmogenus ignotus, 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 ignotus sp. nov. Figures 16E-H , 17

Type material.

Holotype (male): "Brazil: Amazonas: Manaus/ -2.93079, -59.97514, 75 m/ Ducke Reserve, near Station/ 5-10.vi.2018; leg. Short & Team/ Flight Intercept Trap/ BR18-0607-FIT", "HOLOTYPE/ CHASMOGENUS/ ignotus sp. n./ des. Smith & Short" (INPA). Paratypes (6): Brazil: Amazonas: Same data as holotype (5 exs., INPA, SEMC); same locality but trail to Igarape Barro Branco, 6.vi.2018, leg. Short & Team, isolated forest pools, BR18-0606-02A (1 ex., SEMC DNA voucher SLE-1844).

Differential diagnosis.

The strongly asymmetrical parameres, highly reduced basal piece, and extraordinary depth of the aedeagus (Fig. 16E-H ) will easily separate this species from all others except C. tafelbergensis , from which it may be separated by its wider aedeagal profile. 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 mm. Dorsum of head, pronotum and elytra uniformly dark brown. Venter slightly lighter brown. Head. Ground punctation on head fine. Clypeus with anteroposterior emargination which exposes a very narrow, broad gap between clypeus and labrum. Mentum strongly depressed in anterior two-thirds with triangular anteromedial notch. Maxillary palps long, as long as width of head immediately posterior to eyes. Thorax. Ground punctation on pronotum moderately coarse. Surface of prosternum even, not tectiform. Mesoventrite with weak elevation forming a posteromedial longitudinal carina. Metafemora densely and uniformly pubescent in basal nine-tenths. Aedeagus. Aedeagus (Fig. 16E-H ) with median lobe highly modified, appearing as a narrow subparallel-sided strap and partly rotated laterally, with apex extending to the apex of the parameres to slightly beyond. Sclerite of the median lobe extremely well developed and appearing as a thin curved strut that extends the full length of the genitalia. Gonopore oriented laterally (Fig. 16F ); situated more than twice gonopore width below the apex of the median lobe. Parameres asymmetrical, with left paramere wider than right paramere; outer margins of parameres strongly sclerotized, with the sclerotized region on the right paramere thicker than the left. Aedeagus, especially the parameres, thickened, such that it takes on a three-dimensional appearance (Fig. 16F, G ); in lateral view widest at base with dorsal surface flat with ventral surface graduating tapering to the apex. Basal piece short, less than half the length of the parameres; partly obscured by the strongly sclerotized and enlarged base of the median lobe and parameres.

Etymology.

The species name is derived from the Latin ignotus , meaning “strange”, after the bizarre form of the aedeagus.

Distribution.

Only known from the Adolpho Ducke Forest Reserve in Manaus, Brazil.

Biology.

One specimen was collected in an isolated forest detrital pool near Igarape Barro Branco, while another series of specimens came from a flight intercept trap in the forest.

Figures

Figure 1. Maximum likelihood phylogeny of Chasmogenus spp. based on COI sequences. Ultra Fast Bootstrap (UFBS) values are indicated at nodes.

Figure 16. Aedeagi of Chasmogenus spp. A-D C. tafelbergensis A dorsal view B side view C side view D ventral view E-H C. ignotus E dorsal view F side view G side view H ventral view. Scale bar: 0.25 mm.

Figure 17. Distribution of Chasmogenus spp.