Gerris (s. str.) curvus, Polhemus, 2012

Polhemus, J. T., 2012, The water skater genus Gerris Fabricius (Hemiptera: Heteroptera: Gerridae) in Vietnam, with the description of a new species, Zootaxa 3382, pp. 20-28 : 21-25

Gerris (s. str.) curvus sp. n.

( Figs. 1–14)

Etymology. The word curvus refers the shape of the connexival spines in females.

Material examined. Holotype: apterous male, allotype: apterous female, VIETNAM, Dong Nai prov., Cat Tien National Park, Bau Sau ( Crocodile lake ), coll. Tran A.D., 12 Apr. 2009, TAD0909 ( ZMHU).

Paratypes: 4 males, 5 females (apterous), 3 males (macropterous) same locality data as the holotype ( NHMW, ZRC) ; 1 male, 1 female (apterous), same locality, coll. Tran A.D., 07 Nov. 2009, TAD0929 ( ZMHU) ; 1 male, 1 female (macropterous), same locality, 100 m ., water temp. 31°C, coll. J.T. Polhemus, 5 May 1998, CL 3071 ( JTPC) .

Description. Size: apterous form: males, length 7.50–8.00, width 2.31–2.47 (holotype: 8.00, 2.44), females, length 8.35–8.75, width 2.81–2.94 (allotype: 8.60, 2.79); macropterous males: length 7.80–8.20, width 2.34–2.44, macropterous female: length 9.20, width 2.95.

Color ( Figs. 1–3): Apterous form: dorsum mainly dark brown to black; antennae black; head with yellow marking on posterior margin; rostrum mainly dark brown; pronotum with median dark yellow stripe about same length as pronotum; pronotum, pronotal lobe, and metanotum with scattered golden pubescence; front legs mainly black with basal and apical part of femur yellowish brown; middle and hind legs yellow to brown; ventral, lateral sides and abdominal terga yellowish brown, with dense silvery pubescence. Macropterous form: similar to apterous form, wing chiefly brown, wing veins with golden pubescence.

Structural characteristics: Apterous male (holotype): Head width 1.46, interocular width 0.89, eye length 0.71. Lengths of antennal segments 1–4: 1.25: 0.76: 0.73: 1.11. Pronotum length 2.89. Mesosternum length 2.64, metasternum length 0.60. Lengths of leg segments (femur: tibia: tarsus 1: tarsus 2): front leg: 2.25: 1.89: 0.24: 0.32; middle leg: 5.40: 4.36: 2.71: 0.60; hind leg: 5.20: 2.67: 1.08: 0.45. Front femur moderately incrassate, length about 5.2 times of width (width 0.43), front tibia slightly curved. Combined length of abdominal sterna 2–7: 2.18; sternum 7 medially notched (length 0.62) ( Figs. 2, 5). Ventral length of abdominal segment 8: 0.49. Sterna 2–5 slightly impressed medially; sterna 6 and 7 with distinct median impression; connexival angles short; sub-lateral impressions on ventral side of abdominal segment 8 usually covered with silvery pubescence ( Figs. 6, 7). Genitalia: pygophore simple, proctiger pointed; vesical sclerites of endosoma as in Figs. 9–11.

Apterous female (allotype): Head width 1.51, interocular width 0.92, eye length 0.68. Lengths of antennal segments 1–4: 1.32: 0.82: 0.73: 1.14. Pronotum length 3.10. Mesosternum length 2.71, metasternum length 0.67. Lengths of leg segments (femur: tibia: tarsus 1: tarsus 2): front leg: 2.33: 1.88: 0.24: 0.33; middle leg: 5.30: 4.41: 2.64: 0.68; hind leg: 5.20: 2.81: 1.05: 0.48. Front femur moderately incrassate, length about 5.68 times of width (width 0.41), front tibia slightly curved. Combined length of abdominal sterna 2–7: 2.84; sternum 7 length 0.64, posterior margin slightly concave. Connexival spines well produced, reaching apex of proctiger, pointed dorsocaudad (on lateral view) and curved inwards (on dorsal view), thus usually not visible on ventral view ( Figs. 12–14).

Macropterous male: similar to apterous form, but connexival spines distinct and longer that in apterous form ( Fig. 8). Structural measurements as follows: Head width 1.43, interocular width 0.87, eye length 0.67. Lengths of antennal segments 1–4: 1.35: 0.73: 0.73: 1.03. Pronotum length 3.04. Mesosternum length 2.64, metasternum length 0.63. Lengths of leg segments (femur: tibia: tarsus 1: tarsus 2): front leg: 2.30: 1.96: 0.25: 0.35; middle leg: 5.40: 4.26: 2.54: 0.71; hind leg: 5.20: 2.64: 0.86: 0.51. Front femur length about 6.0 times of width (width 0.38). Combined length of abdominal sterna 2–7: 2.40; sternum 7 length 0.63. Ventral length of abdominal segment 8: 0.44. Wings not reaching tip of proctiger, wing length ca. 4.80.

Comparative notes. According to Andersen (1993), Gerris (s. str.) nepalensis Distant, 1910 stands alone as a single-species group, which is defined by the following characteristics: long and slender antennae and legs; middle of head shiny; abdominal tergum distinctly shiny; vesical sclerites simple; well-produced connexival processes. Gerris curvus sp. n. is closely related to Gerris nepalensis as it fits well in the diagnosis of the G. nepalensis species group (sensu Andersen, 1993) but it differs from G. nepalensis in several characteristics. In males, the abdominal venter of Gerris curvus sp. n. is medially impressed, especially in sterna 6–7, while in G. nepalensis , there is no median impression. The endosoma structures are similar, but the lateral sclerites of Gerris curvus sp. n. are more slender, and their posterior part not as broadened as in G. nepalensis . In females, tergite 7 of Gerris curvus sp. n. is distinctly narrower in the posterior part while in that of G. nepalensis the posterior width is subequal to the anterior width. The connexival spines in females are also distinctly different in two species: straight, parallel and rather pointed caudad in G. nepalensis ; pointed dorsocaudad (in lateral view) and curved inwards (in dorsal view) in Gerris curvus sp. n.