Chasmogenus acuminatus, 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 acuminatus sp. nov. Figures 5A-C , 9B , 15H-I , 18 , 21E , 22C, D

Chasmogenus sp. X Short, 2013: 87 (in part); Short & Kadosoe, 2011: 87 (in part), Short, Salisbury, & La Cruz 2018: 193 (in part).

Type material.

Holotype (male): "Suriname: Sipaliwini District/ 2°21.776'N, 56°41.861'W, 237 m/ Camp 3 Wehepai; leg. Short &/ Kadosoe; sandy forest creek/4-6.ix.2010; SR10-0904-01A/ CI-RAP Survey", "DNA VOUCHER/ Extraction #/ SLE-1822", "HOLOTYPE/ CHASMOGENUS/ acuminatus sp. n./ des. Smith & Short." (NZCS). Paratypes (321): Brazil: Amapa: Oiapoque (c. 22 km S) on BR-156, leg. Short, forested detrital pools, BR18-0720-01B (1 ex., SEMC, DNA voucher SLE1850). Para: Vale do Paraíso, ca. 55 km N. Alenquer, -1.49292, -54.51566, leg. Short, detrital pool, BR18-0203-01B (1 ex., SEMC, DNA voucher SLE1623). French Guiana: Petit-Saut, 5.070, -53.029 (2 exs., SEMC, DNA Vouchers SLE516 and SLE1840). Guyana: Region 9: along road to Parabara, 2°09.557'N, 59°17.569'W, 268 m, 1.xi.2013, leg. Short, Isaacs and Salisbury, forest pools near Mushai Wao, GY13-1101-02A (4 exs., SEMC); Parabara, trail to mines, 2°05.095'N, 59°14.174'W, 250 m, 2.xi.2013, leg. Short, Isaacs and Salisbury, detrital pools in forest, GY13-1102-01A (2 exs., SEMC); North of Parabara, Bototo Wau Creek, 2°10.908'N, 59°20.306'W, 289 m, 31.x.2013, leg. Short, Isaacs and Salisbury, stream margins, GY13-1031-01A (3 exs., SEMC); Parabara north side of river, 2°06.492'N, 59°13.653'W, 274 m, 3.xi.2013, detritus margins and leaf packs, GY13-1103-02A (2 exs., SEMC, including DNA Voucher SLE1086). Region 6: Upper Berbice circa 1 km south of Basecamp 1, 4°09.241'N, 58°10.627'W, 109 m, 25.ix.2014, leg. Short and La Cruz, margins of creek with leaf packs and mud, GY14-0925-01B (2 exs., SEMC); Upper Berbice Basecamp 1, 4°09.289'N, 58°10.717'W, 96 m, 21.ix.2014, leg, Short, Salisbury and La Cruz, muddy detrital pools in drying creekbed near camp, GY14-0921-02A (5 exs., SEMC, CBDG); same data as previous except: 24.ix.2014, margins of basecamp creek, GY14-0924-01A (1 ex., SEMC); Upper Berbice circa 1 km west of Basecamp 1, 4°09.143'N, 58°11.207'W, 105 m, 22.iv.2014, leg, Short, Salisbury and La Cruz, margins of creek, GY14-0921-03H (2 exs., SEMC); same data as previous except: 21.ix.2014, leg. A. Short, sandy stream, GY14-0921-03A (1 ex. SEMC); Upper Berbice Basecamp 2, 4°45.301'N, 58°00.404'W, 49 m, 26.ix.2014, leg. Short, Salisbury and La Cruz, shallow detrital pool in forest draining into creek, GY14-0926-01A (2 exs. SEMC). Region 8: Konawaruk River, Basecamp 2 (NARIL basecamp), 5°07.539'N, 59°06.732'W, 80 m, 15.ix.2014, leg. Salisbury and La Cruz, unnamed clear water creek, slow flowing and shallow, GY14-0915-02 (7 exs., SEMC); Upper Potaro Camp (circa 7 km northwest of Chenapau), 5°0.660'N, 59°38.283'W, 484 m, 11.iii.2014, leg. Short, Baca, Salisbury and La Cruz, Potaro margin trail with wet detritus in sandy area, GY14-0311-04A (1 ex., SEMC). Region 10: Upper Berbice logging road KM 1, 5°03.892'N, 58°03.303'W, 71 m, 29.ix.2014, leg. Short, Salisbury and La Cruz, marsh and creek, GY14-0929-01B (1 ex., SEMC). Suriname: Sipaliwini District: Camp 3, Werehpai, 2°21.776'N, 56°41.861'W, 237 m, 3-7.ix.2010, leg. Short and Kadosoe, detrital pools forest, 2010 CI-RAP Survey, SR10-0903-02A (4 exs., SEMC); same data as previous except: 3.ix.2010, pooled up detrital creek, 2010 CI-RAP Survey, SR10-0903-01A (54 exs., NZCS, SEMC, INPA); same data as previous except: 4-6.ix.2010, sandy forest creek, SR10-0904-01A (26 exs., SEMC, including DNA vouchers SLE1822 and SLE1823); Camp 2 on Sipaliwini River 2°10.973'N, 56°47.235'W; 210 m, 28.viii.2010, Short and Kadosoe, small detrital stream, CI-RAP Survey, SR10-0828-03A (27 exs., SEMC); same data as previous except: 30.viii.2010, forest creek, SR10-0831-01A (24 exs., SEMC); same data as previous except: 31.viii.2010, sandy forest creek with detritus, SR10-0831-01B (38 exs., SEMC); same data as previous except: 28-29.viii.2010, large forest stream, SR10-0828-02A (16 exs., SEMC, including DNA voucher SLE1820); Camp 1 on Kutari River, 2°10.521'N, 56°47.244'W, 228 m, 20.viii.2010, leg. Short and Kadosoe, forest stream, CI-RAP Survey, SR10-0820-01A (7 exs., SEMC); same data as previous except: 19.viii.2010, SR10-0819-02A (1 ex., SEMC); same data as previous except: 19.viii.2010, forested swamp, SR10-0819-01A (39 exs., SEMC); same data as previous except: 19-24.viii.2010, leg. Short, Kadosoe, and Larsen, FIT, SR10-0819-TN1 (1 ex., SEMC); rapids on Kutari River, 2°19.280'N, 56°52.595'W, 224 m, 18.viii.2010, leg. A. E. Z. Short, forest stream, 2010 CI-RAP Survey, SR10-0818-01A (1 ex., SEMC); Camp 2 on Sipaliwini River, 2°10.973'N, 56°47.235'W, 210 m, 29-30.viii.2010, leg. Short and Kadosoe, inselberg, 2010 CI-RAP Survey, SR10-0829-01A (1 ex. SEMC); Camp 1 on Kutari River, 2°10.521'N, 56°47.244'W, 228 m, 22.viii.2010, Short and Kadosoe, forest swamp, CI-RAP Survey, SR10-0822-02A (7 exs., SEMC including DNA Voucher SLE 445); Camp 1 Upper Palumeu, 2.47700N, 55.62941W, 275 m, 10-16.iii.2012, leg. A. Short, 2012 CI-RAP Survey, Flight Intercept Trap, SR12-0310-TN1 (1 ex. SEMC); Raleighvallen Nature Reserve, base of Voltzberg, 4°40.432'N, 56°11.079'W, 86 m, 16.iii.2016, leg. Short et al., pooled up stream, SR16-0316-01B (10 exs., SEMC, including DNA vouchers SLE1838 and SLE1839); Raleighvallen Nature Reserve Lolopaise area, 4°42.48'N, 56°13.15908'W, 24 m, 18.iii.2016, leg. Short et al., intermittent stream margins and flotation, SR16-0318-01D (3 exs., SEMC, including DNA voucher SLE1849); Raleighvallen Nature Reserve, trail from plateau to Voltzberg, 17.iii.2016, leg. J. Girón, stream with roots and mud, SR16-0317-04A (3 exs., SEMC); Raleighvallen Nature Reserve, Fungu Island, 4°43.459'N, 56°12.658'W, 30 m, 14.iii.2016, leg. A. Short, isolated river margin pools with rocky bottom, SR16-0314-01E (1 ex., SEMC); Raleighvallen Nature Reserve Voltzberg Station, 04°40.910'N, 56°11.138'W, 78 m, 29.vii.2012, leg. A. Short and C. McIntosh, detrital side pool, SR12-0729-02B (2 exs., SEMC); same data as previous except: 29.vii.2012, leg. Short, Maier, McIntosh, and Kadosoe, stream margins, SR12-0729-02A (3 exs., SEMC); Raleighvallen Nature Reserve, trail to Raleighvallen, 04°42.480'N, 56°13.159'W, 24 m, 27.vii.2012, leg. C. McIntosh, detrital pools near creek in forest, SR12-0727-03D (5 exs., SEMC); Raleighvallen Nature Reserve Voltzberg trail, 04°40.910'N, 56°11.138'W, 78 m, 30.vii.2012, leg. A. Short and C. McIntosh, detrital pools along stream, SR12-0730-01B (6 exs., SEMC, including DNA Voucher SLE1081); CSNR Tafelberg Summit near Augustus Creek Camp, 3°55.600'N, 56°11.300'W, 600 m, 16.viii.2013, leg. Short and Bloom, pond on trail into Arrowhead basin, SR13-0816-02A (1 ex., SEMC); same data as previous except: 22.viii.2013, detrital creek, SR13-0822-01A (1 ex., SEMC); Sipaliwini Savanna Nature Reserve, Four Brothers Mountain, 2°00'20.5"N, 55°58'08.9"W, 337 m, 31.iii.2017, leg. A. Short, detrital pools, SR17-0331-01D (1 ex., SEMC DNA Voucher SLE1619); Kabalebo Nature Resort, Moi Moi Creek, leg. Short, detrital pool, SR19-0310-01G (2 exs., SEMC, DNA vouchers SLE1804 and SLE1805).

Differential diagnosis.

Among species that have a broad clypeal emargination and the apex of the median lobe extending past the apex of the parameres, C. acuminatus may be distinguished by the straight outer margin (Fig. 15H, I ) of the parameres, (distinctly sinuated in the similar and regionally co-occurring C. undulatus , C. ligulatus , and C. pandus ). 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 3.4-3.9 mm. Body form elongate oval with slightly curved lateral margins. Dorsum of head brown to dark brown, clypeus distinctly paler brown (Fig. 9B ). Pronotum and elytra uniformly dark orange-brown (Fig. 5A ). Venter dark orange centrally, dark red-brown distally (Fig. 5C ). Head. Ground punctation on head coarse. Clypeus with anteromedial emargination, which exposes a broadly rounded to angulate gap between the clypeus and labrum (Fig. 9B ). Mentum strongly depressed in anterior half with a triangular to subtriangular anteromedial notch. Maxillary palps long, longer than width of head immediately posterior to eyes. Thorax. Ground punctation on pronotum moderately coarse (Fig. 5A ). Prosternum tectiform. Mesoventrite with weak elevation forming a thin posteromedial longitudinal carina. Metafemora densely pubescent in basal nine-tenths (Fig. 5C ). Aedeagus. Aedeagus (Fig. 15H, I ) with median lobe subtriangular in shape, widest at base and gradually tapering along entire length; apex acute, distinctly extending beyond the apex of the parameres. Sclerite of the median lobe expanded, but very narrow and weakly developed, apex not reaching the apex of the parameres. Gonopore situated ca. one gonopore width below the apex of the median lobe. Parameres symmetrical, with outer margins very slightly inwardly curved a long length; width of each paramere gradually narrowed to a blunt (Fig. 15H ) to slightly acute (Fig. 15I ) apex. Basal piece short, ca. one-third the length of the parameres.

Etymology.

The species name is derived from the Latin acuminatus , meaning “pointed”, after the condition of the aedeagus, in which the apex of the median lobe is extended and forms an acute point.

Distribution.

Known from a broad range in the eastern Guiana Shield region of South America, from Guyana east to the state of Amapá, Brazil and south to the Amazon River (Fig. 18 ).

Biology.

This species is relatively widespread and one of the most commonly encountered Chasmogenus in the eastern Guiana Shield. It is found in forested habitats, typically associated with detrital pools, the margins of streams and creeks, and forested swamps (Figs 21E , 22C, D ). Some specimens have been collected in flight intercept traps (FITs).

Remarks.

There is a high level of genetic diversity in the species (Fig. 1 ), with observed COI divergence as high as 6% between some individuals. However, we did not identify any substantial corresponding morphological variation and believe it is best to consider this intraspecific genetic variation for the time being.

Figures

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

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 9. Dorsal view of heads of Chasmogenus spp. A C. amplius B C. acuminatus C C. berbicensis D C. clavijoi E C. undulatus F C. gato.

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 18. Distribution of Chasmogenus spp. Localities marked with stars / triangles indicate populations that were sampled for DNA in Fig. 1.

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).

Figure 22. Habitat of Chasmogenus spp in Guyana. A Type locality and habitat for C. berbicensis, Guyana, margin / detrital sandbar of the upper Berbice River (collecting event GY 14 - 0922 - 02 A) B type locality and habitat for C. undulatus Guyana, near Ayanganna airstrip (collecting event GY 14 - 0317 - 01 A) C habitat for C. acuminatus and C. guianensis, Guyana, small tributary of the upper Berbice River (collecting event GY 14 - 0924 - 01 A) D habitat for C. acuminatus (collecting event GY 13 - 1103 - 02 A).