Chasmogenus australis Garcia , 2000

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

publication ID	https://dx.doi.org/10.3897/zookeys.934.49359
publication LSID	lsid:zoobank.org:pub:B9F2C8D8-C031-4191-B6F5-1E78D4D6881E
persistent identifier	https://treatment.plazi.org/id/790D65B5-C650-57C9-A8DA-37CBE1C77EB9
treatment provided by	ZooKeys by Pensoft
scientific name	Chasmogenus australis Garcia , 2000
status

Treatment

Chasmogenus australis Garcia, 2000 View in CoL Figures 4D-F View Figure 4 , 6 View Figure 6 , 8B View Figure 8 , 13A-D View Figure 13 , 18 View Figure 18 , 20C-F View Figure 20

Chasmogenus australis García, 2000: 52.

Type material examined.

Holotype (Male): "Venezuela, Apure/ Mcipo. Achaguas, / parroquia Saman de/ Apure, 25-26/VIII/1997", "Colectores:/ M. García”, "[Barcode]/ MALUZ10146/ LUZ-Venezuela", "Holotipo [male symbol]/ Chasmogenus / australis / Dcrip. M. García, 1999" (MALUZ). The label data of the holotype (Fig. 6 View Figure 6 ) differs slightly from that given in the original description. The locality is identical as listed in García (2000), but the date and collector data differ (given as 13 August 1998 and M. García & E. Gomez). The type is an undissected male, the aedeagus is visibly protruding from the abdomen. We also examined a permanent genitalia slide that is labeled as this species (Fig. 13A View Figure 13 ).

Additional material examined.

Brazil: Roraima: Circa 30 km southeast of Caracarai on BR-174, 1°35.091'N, 61°00.118'W, 80 m, 16.i.2018, leg. Short, Benetti, and Santana, marsh, BR18-0116-05A (37 exs., INPA, SEMC, including DNA Voucher SLE1774); Murupu River at BR-174 north of Boa Vista, 3°01.276'N, 60°46.565'W, 75 m, 13.i.2018, leg. A. E. Z. Short, muddy backwaters of stream, BR18-0113-01A (3 exs., SEMC); Vicinal 30, 00°43'50.2"N, 060°25'58"W, 77 m, 10.i.2018, leg. Short and Benetti, large roadside ditch with dense vegetation, BR18-0110-03A (24 exs., INPA, SEMC, including DNA voucher SLE1624); ca. 16 km west of Amajari on BR-203, 3°36.874'N, 61°33.470'W, 125 m, 13.i.2018, leg. Short, Benetti, and Santana, marsh, BR18-0113-04A (9 exs., SEMC); Circa 26 km south of Cantá, 2°22.547'N, 60°33.538'W, 93 m, 11.i.2018, leg. Short, marsh with lots of emergent vegetation, BR18-0111-02A (1 ex., SEMC); Circa 7 km south of Iracema on BR-174, 2°6.277'N, 61°4.922'W, 59 m, 16.i.2018, leg. Short, Benetti, and Santana, marsh and palm swamp, BR18-0116-01A (1 ex., SEMC); Jundia on BR-174, 00°12'20.3"S, 060°41'35.1"W, 57 m, 10.i.2018, leg. Short and Benetti, marsh with lots of emergent vegetation, BR18-0110-01A (1 ex.., SEMC); Sitio Bem Querer ca. 3 km west, 1°56.131'N, 61°01.737'W, 80 m, 16.i.2018, leg. Short, Benetti, and Santana, BR18-0116-04A (2 exs., SEMC); near Boa Vista, 2°44.558'N, 60°47.179'W, 105 m, 15.i.2018, leg. Short, Benetti, and Santana, UV light by drying marsh, BR18-0115-03A, (1 ex., SEMC); BR-174, c. 50 km NW Boa Vista, 3 18.348'N, 60 51.458'W, 100 m, 13.i.2018, leg. Short, marsh, BR18-0113-02A (1 ex., SEMC, DNA Voucher 1629). French Guiana: Yiyi, 5.419, -53.050 (1 ex., SEMC, DNA Voucher SLE1856). Guyana: Region 9: near Kusad Mountains, 2°52.204'N, 59°55.003'W, 124 m, 27.x.2013, leg. Short, Isaacs, and Salisbury, marshy area, GY13-1027-01A (2 exs., SEMC); Ziida Wao Creek near Kusad Mountains, 2°49.724'N, 59°48.546'W, 121 m, 25.x.2013, leg. Short, Isaacs, and Salisbury, stagnant vegetated creek, GY13-1025-02A (3 exs., CBDG, SEMC, including DNA Voucher SLE1615); Venezuela: Barinas: ca. 13 km southeast of Ciudad Bolivia, 8°19.394'N, 70°28.238'W, 173 m, 25.i.2012, leg. Short, Arias, and Gustafson, marsh, VZ12-0125-02A (6 exs., SEMC, including DNA voucher SLE1080). Cojedes: Rio Caiman Grande at San Brano, 9°39.246'N, 68°11.860'W, 137m, 20.i.2012, leg. Short, Arias, and Gustafson, river margin, VZ12-0120-03A (2 exs., SEMC). Monagas: South of Maturin, 9°16.398'N, 62°56.246'W, 22 m, 2.ii.2010, leg. Short, García, and Joly, morichal margin, VZ10-0202-02A (6 exs., SEMC); between Morichal Largo and Tembledor, 9°05.798'N, 62°43.618'W, 29 m, 2.ii.2010, leg. Short, García, and Joly, margins of vegetated pond, VZ10-0202-03A (11 exs., MIZA, SEMC; including DNA voucher SLE1621). Zulia: Sabana de Machango, 10.043017, -71.007133, 35 m, 29.i.2012, leg. Short, Arias and Gustafson, margin of artificial pond, VZ12-0129-03A (1 ex., SEMC, DNA Voucher SLE1082).

Differential diagnosis.

The small size (<3.5 mm) and very pale dorsal coloration (Fig. 4D-F View Figure 4 ) serves to separate C. australis from most other small-bodied regional congeners, as well as its distinctive aedeagus. It also almost exclusively occurs in open marsh habitats, whereas most all other congeners are typically found in other types of habitat.

Description.

Size and color. Total body length 3.0-3.4 mm. Body form elongate oval with slightly curved lateral margins. Dorsum of head bicolored; frons dark brown, clypeus and labrum light tan-brown (Fig. 8B View Figure 8 ). Pronotum and elytra light tan-orange, light golden yellow marginally (Fig. 4D View Figure 4 ). Venter almost entirely light golden-brown, venter of head and lateral margins of metaventrite light brown (Fig. 4F View Figure 4 ). Tibiae orange-brown. Head. Ground punctation on head fine, labrum with slightly finer punctation. Clypeus with anteromedial emargination, which exposes a wide trapezoidal-shaped gap between clypeus and labrum (Fig. 8B View Figure 8 ). Mentum weakly to moderately depressed on anterior half with subtriangular anteromedial notch. Maxillary palps long, longer than width of head immediately posterior to eyes. Thorax. Ground punctation of pronotum moderate. Prosternum tectiform. Mesoventrite with weak elevation forming a thin posteromedial longitudinal carina. Metafemora densely pubescent with long golden setae in basal six-sevenths (Fig. 4F View Figure 4 ). Aedeagus. Aedeagus (Fig. 13A-D View Figure 13 ) with outer margins of median lobe strongly situate, such that it appears constricted in the middle; above constriction, margins tapering to form a weakly pointed apex, which 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 with outer margins weakly and evenly curved (Fig. 13A View Figure 13 ) to slightly sinuate near the apex (Fig. 14B-D View Figure 14 ), with outer apex bluntly rounded and inner apex appear as a right angle. Basal piece long, subequal to slightly shorter than the length of the parameres.

Distribution.

This species has a very broad range, occurring from northwestern Venezuela to the coast of French Guiana (Fig. 18 View Figure 18 ). It was originally described from the central region of the Venezuelan Llanos. We have collected it across a very broad range in Venezuela, including the Maracaibo Basin, across the Llanos region, as well as in the Rupununi/Roraima savannah complex in northern Brazil and Guyana. We also report it from the coastal savannahs of French Guiana.

Biology.

Unlike most Chasmogenus , C. australis is almost exclusively associated with lentic or open marsh habitats (Fig. 20C-F View Figure 20 ). A few specimens have been taken along the muddy and vegetated margins of large, slow-flowing rivers (morichales).

Remarks.

Despite its broad range, sequenced populations of C. australis displayed virtually no genetic variation in COI, with less than 1% divergence between all sampled individuals spanning more than 2000 km from western Venezuela to French Guiana, south to the state of Roraima, Brazil. We also note the strong similarities in aedeagal morphology and habitat to C. sapucay Fernández, which was originally described from Argentina and Paraguay but whose range was recently extended into Brazil ( Fernández 1986, Clarkson and Ferreira-Jr 2014). Although we suspect C. australis may be a junior subjective synonym of C. sapucay , we are refraining from making any nomenclatural changes until the two taxa can be compared in more detail.