Rhyacobates constrictus, Tran, A. D. & Nguyen, X. Q., 2016

Tran, A. D. & Nguyen, X. Q., 2016, Three new species of the water strider genus Rhyacobates Esaki, 1923 (Hemiptera: Gerridae) from Vietnam, Zootaxa 4121 (5), pp. 501-516 : 508-512

Rhyacobates constrictus sp.n.

( Figs. 25–39 )

Material examined. Holotype (apterous female) and allotype (apterous male), VIETNAM, Phu Tho Prov., Xuan Son N’Park, Lap stream, site 1, at Ngoc waterfall, 21°07.817’N 104°55.506’E, 390 m asl., coll. Tran A.D. et al., 5 June 2013, TAD1331 ( ZMHU).

Paratypes: VIETNAM: Phu Tho Prov.: 8 males, 7 females (apterous), 1 female (macropterous, de-alated), same locality data as holotype ( ZMHU, ZRC); 2 males, 3 females (apterous), Xuan Son N’Park, Lap stream, site 2, first concrete bridge from Ngoc waterfall, 21°08.008’N 104°55.768’E, 330 m asl., coll. Tran A.D. et al., 5 June 2013, TAD1332 ( ZMHU); 1 female (apterous), Xuan Son N’Park, Lap stream, site 3, second concrete bridge from Ngoc waterfall, 21°08.299’N 104°56.26’E, 268 m asl., coll. Tran A.D. et al., 5 June 2013, TAD1333 ( ZMHU); 1 male (apterous), Xuan Son N’Park, Kim Thuong, Tan Ong stream, site 2, ca. 2km from Chin Tang waterfall, 21°04.201’N 104°56.919’E, 340 m asl., coll. Tran A.D. et al., 28 August 2013, TAD1341 ( ZMHU); 2 females (apterous), Xuan Son N’Park, Lap stream, site 1, at Ngoc waterfall, coll. Tran A.D. et al., 30 August 2013, TAD1352 (GPS data same as TAD1331) ( ZMHU); 2 males, 2 females (apterous), Xuan Son N’Park, Lap stream, site 2, first concrete bridge from Ngoc waterfall, coll. Tran A.D. et al., 30 August 2013, TAD1353 (GPS data same as TAD1332) ( ZMHU); 5 males, 2 females (apterous), Xuan Son N’Park, Lap stream, site 3, second concrete bridge from Ngoc waterfall, coll. Tran A.D. et al., 30 August 2013, TAD1354 (GPS data same as TAD1333) ( ZMHU, NHMW); 3 males, 1 female (apterous), Xuan Son N’Park, Lap stream, site 1, at Ngoc waterfall, coll. Nguyen T.S. et al., 27 August 2014, TS1409 (GPS data same as TAD1331) ( ZMHU); 2 males, 2 females (apterous), Xuan Son N’Park, Lap stream, site 2, first concrete bridge from Ngoc waterfall, coll. Nguyen T.S. et al., 27 August 2014, TS1410 (GPS data same as TAD1332) ( ZMHU); 1 male, 2 females (apterous), Xuan Son N’Park, Lap stream, site 2, first concrete bridge from Ngoc waterfall, coll. Nguyen T.S. et al., 23 May 2015, TS1512 (GPS data same as TAD1332) ( ZMHU); 2 males (apterous), Xuan Son N’Park, Lap stream, site 2, first concrete bridge from Ngoc waterfall, coll. Nguyen T.S. et al., 26 August 2015, TS8512 (GPS data same as TAD1332) ( ZMHU).

Description. Size: apterous morph: males, length 6.90–7.10 (allotype 6.95), width 2.20–2.30 (allotype 2.24); females, length 8.7–9.4 (holotype 9.0), width 3.08–3.20 (holotype 3.20); macropterous morph (de-alated): female, length 9.10, width 3.23.

Colour ( Figs. 25, 26 ): Dorsum of body mainly black, covered with silvery pubescence, especially dense on thoracic pleura, metacoxa and abdomen. Dorsum of head yellow with median, longitudinal brown mark on anterior three quarters. Antennae mainly dark brown, segment 4 with whitish area in distal two-fifths. Pronotum mainly black with median yellow mark (in female, width of mark about one third of pronotum mark; in male, yellow mark narrower), anterolateral corners of pronotum yellow. Mesonotum and metanotum black, without yellow mark. Abdominal terga chiefly black, except abdominal apex yellowish and brown (in proctiger and pygophore of male; and in abdominal segment 7 and genitalia of female). In both sexes, venter of body covered with dense silvery pubescence. Venter of female mostly yellow, except mesosternum, mesopleuron and anterior third of metasternum black. Venter of male with mesosternum, mesopleuron and metasternum black, abdominal sternum 2 black or brown, the remaining parts yellow. All acetabulae, coxae and trochanters yellow. Fore femur yellow with brown longitudinal stripe dorsally. Middle and hind femora yellow at basal part, dark brown at distal part. Fore tibia and tarsus dark brown; other tibiae and tarsi yellowish brown.

Apterous female (holotype): Head width 1.43, interocular width 0.57, eye length (dorsal view) 0.63. Lengths of antennal segments 1–4: 4.30: 1.21: 1.50: 1.09. Pronotum broader than long, length 0.81, width 1.53; mesonotum length 2.56, metanotum length 1.07. Mesopleuron with scattered long erect bristle-like brown hairs. All coxae with rings of dark bristle-like hairs at apical margins. Fore trochanter with long hairs on ventral side. Lengths of leg segments (femur: tibia: tarsus 1: tarsus 2): fore leg: 4.35: 3.55: 2.00: 0.94; middle leg: 11.50: 6.70: 4.10: 0.44; hind leg: 11.80: 5.19: 0.14: 0.22. Fore femur slender (width 0.42), venter of femur with row of 11 dark bristle-like hairs, with scattered soft long hairs, sub-apical part with small tooth-like elevation, sometimes indistinct ( Fig. 27 ). Abdomen relatively short, ventral length 3.85; abdominal apex directed dorsocaudad ( Fig. 34 ). Tergum 1 posteromedially swollen ( Figs. 36 ). Connexival margin of segments 1–5 narrow, of segment 6 thickened. Abdominal segment 7 prolonged, completely enclosing genital segments, tergum 7 short (length 0.45), posterior part thickened, medially notched on posterior margin; sternum 7 (length 1.79) about 4.0 times as long as tergum 7; connexival and posterolateral margins expanded dorsad, folded inwards, meeting in middle of abdominal dorsum (holotype, Fig. 36 ) or overlapping each other ( Fig. 38 ), thus covering most of genital segments; sternum 7 tapering caudad, posterior margin with narrow median process, apex of process narrowly rounded ( Figs. 36–39 ).

Apterous male (allotype): Head width 1.32, interocular width 0.49, eye length 0.65. Lengths of antennal segments 1–4: 3.65: 1.10: 1.50: 1.06. Pronotum broader than long, length 0.72, width 1.41; mesonotum length 2.13, metanotum length 0.79. Mesopleuron with scattered long erect bristle-like brown hairs. Lengths of leg segments: fore leg: 3.90: 3.20: 0.98: 0.69; middle leg: 10.30: 5.81: 3.32: 0.40; hind leg: 10.40: 4.00: 0.12: 0.18. Fore femur slender (width 0.45), with row of seven bristle-like hairs and few scattered soft long hairs on venter, sub-apical part with small tooth-like elevation. Middle trochanter without spines, middle femur with scattered small spines, not arranged in distinct row ( Fig. 28 ). Other leg structures similar to those of female. Abdomen relatively short, ventral length 2.15. Length of sternum 7: 0.30, posterior margin slightly concave. Genitalia: slightly directed downwards; venter of abdominal segment 8 length (in-situ) 0.15; proctiger laterally widened forming broad, angular lobe on each side ( Fig. 29 ); pygophore of moderate size, apical margin rounded; paramere relatively long, curved at basal fourth, strongly thickened at middle, then tapering towards narrow apex, apex slightly directed inwards, setae mostly on distal part ( Figs. 30–32 ); endosomal sclerites as in Fig. 33 .

De-alated macropterous female: Head width 1.46, interocular width 0.56, eye length 0.67. Lengths of antennal segments 1–4: 4.25: 1.17: 1.42: 1.08. Pronotum covering most of mesonotum, length 3.35, width (across humeri) 2.56; metanotum length 0.83. Lengths of leg segments: fore leg: 4.35: 3.60: 1.91: 0.95; middle leg: 11.50: 6.80: 4.15: 0.46; hind leg: 12.10: 5.30: 0.14: 0.23; width of fore femur 0.44. Other structural characteristics similar to apterous females.

Macropterous male: unknown.

Etymology. The species epithet constrictus refers to the posteriorly constricted abdominal sternum 7 of the female, which holds genital segments within.

Remarks. Rhyacobates constrictus sp.n. can be easily separated from all of its congeners by the following characteristics: in both sexes, the meso- and metanota are totally black, without yellow marking ( Fig. 26 ); in the female, the abdomen is curved dorsad ( Fig. 34 ), the connexival and posterolateral margins of sternum 7 expand dorsad and fold inwards; thus, sternum 7 covers most of the genital segments ( Figs. 35–39 ), sternum 7 tapers caudad, with a narrow median process on the posterior margin, the apex of the process is narrowly rounded ( Figs. 36–39 ); the male paramere is strongly thickened at the middle ( Figs. 30, 32 ). This new species is the only species of Rhyacobates that has no yellow marking on the meso- and metanota (in other species of Rhyacobates , at least the mesonotum has yellow marking). Compared with other species of Rhyacobates , the shape and structure of sternum 7 of the female is unique for R. constrictus sp.n. The median process on sternum 7 is found in R. abdominalis Andersen & Chen, 1995 and R. recurvus Andersen & Chen, 1995 , but they are not as prominent as in R. constrictus sp.n.; and the connexival margin of sternum 7 without a process also separates R. constrictus sp.n. from these two taxa. Males of R. constrictus sp.n. can be easily separated from R. abdominalis by the absence of yellow marking on the meso- and metanota and the shape of the paramere. To date, only the female of R. recurvus has been described; the description of the male is not available. Thus, we are unable to compare the male of R. constrictus sp.n. with that of R. recurvus .

Habitats. Specimens of R. constrictus sp.n. were collected at fast flowing sections of streams shaded by pristine forest at elevation above 250 m ( Figs. 24, 25 ). They were found skating along streams with adults and nymphs in a mixture. Individuals of this species were also found often resting on partially submerged rocks in the middle the stream ( Fig. 26 ).

Distribution. Vietnam: Phu Tho.

Figures

FIGURES 24 – 26. (24) Habitat of type locality of Rhyacobates constrictus sp. n. (25) A copulating pair of R. constrictus sp. n., skating on the fast current of the stream. (26) A copulating pair of R. constrictus sp. n., resting on the emerged rocks in the middle of the stream (photographed by Tran Anh Duc).

FIGURES 27 – 39. Morphological features of Rhyacobates constrictus sp. n. (27) right fore leg of female. (28) basal part of right middle leg of male, ventral view. (29) proctiger. (30 – 32) left paramere from three different views. (33) endosomal sclerites. (34) body of female, lateral view. (35) apex of abdomen of female, lateral view. (36) abdomen of female holotype, dorsal view. (37) apex of abdomen of female holotype, ventral view. (38, 39) apex of abdomen of female paratype, dorsal and ventral view.