DSpace at VNU: Three new species of the water strider genus Rhyacobates Esaki, 1923 (Hemiptera: Gerridae) from Vietnam

DSpace at VNU: Three new species of the water strider genus Rhyacobates Esaki, 1923 (Hemiptera: Gerridae) from Vietnam t...

Zootaxa 4121 (5): 501–516 http://www.mapress.com/j/zt/ Copyright © 2016 Magnolia Press Article ISSN 1175-5326 (print edition) ZOOTAXA ISSN 1175-5334 (online edition) http://doi.org/10.11646/zootaxa.4121.5.1 http://zoobank.org/urn:lsid:zoobank.org:pub:BCADF85B-CB84-4694-963A-AF9F0E3F40D4 Three new species of the water strider genus Rhyacobates Esaki, 1923 (Hemiptera: Gerridae) from Vietnam A.D TRAN & X.Q NGUYEN Tran Anh Duc & Nguyen Xuan Quynh, Department of Invertebrate Zoology, Faculty of Biology, Hanoi University of Science (Vietnam National University, Hanoi), 334 Nguyen Trai, Thanh Xuan, Hanoi, Vietnam E-mail: tran.anhduc@hus.edu.vn Abstract Three new species: Rhyacobates zetteli sp.n., R angustus sp.n., and R constrictus sp.n., all from mountainous areas of northern Vietnam, are described With these new taxa, a total of six species of Rhyacobates has been recorded from Vietnam A key to species of Rhyacobates occurring in Vietnam is provided Key words: Gerridae, Rhyacobates, new species, Vietnam Introduction The genus Rhyacobates Esaki, 1923 has its distribution in China, Korea, Taiwan, northern Thailand, northern Myanmar, and northern Vietnam (Andersen & Chen 1995; Tran & Yang 2006) Species of Rhyacobates are strong skaters, occupying fast flowing parts of rivers and streams Although the distribution range of the genus is relatively wide, most species are only known from their type localities, except R takahashii Esaki, 1923 and R abdominalis Andersen & Chen, 1995 Rhyacobates takahashii is endemic to Taiwan but widespread within the island (Andersen & Chen 1995) Rhyacobates abdominalis is found in two disjunct general localities: eastern China (Guangdong Prov.) and northwestern Vietnam (Lao Cai Prov.) (Andersen & Chen 1995; Tran & Yang 2006) Only R malaisei Andersen & Chen, 1995 is found in three countries: China (Yunnan Prov.), Myanmar, and Thailand (Chiang Mai Prov.) (see Andersen & Chen 1995), but these areas are geographically close to each other This fact suggests that our knowledge on the distribution of species of Rhyacobates is still poor and there have not been adequate sampling efforts Andersen & Chen (1995), in their revision of this genus, recognised nine species, excluding Rhyacobates imadatei Miyamoto, 1967 Andersen & Chen (1995) believed that this species did not belong to Rhyacobates due to various morphological inconsistencies with their generic definition Subsequent studies by Polhemus & Zettel (1997), Zettel & Thirumalai (2001a, b), and Chen et al (2005) also acknowledged the incorrect placement of this species in Rhyacobates, but no taxonomic decision was made Eventually, Zettel (2009) placed Rhyacobates imadatei Miyamoto in a genus of its own, Celerobates Zettel, 2009 Tran & Yang (2006) provided the first records of Rhyacobates from Vietnam, including descriptions of two new species, R anderseni Tran & Yang, and R gongvo Tran & Yang The present paper reports three more species from Vietnam, all new to science and they are described herein Thus, to date, the total number of described species of the genus has been raised to 14 Material and methods Materials used in this study have been deposited in the following museums or collections: NHMW ZMHU Natural History Museum, Vienna (Austria) Zoological Collection of the Biological Museum, Hanoi University of Science (Vietnam) Accepted by R Sites: 10 May 2016; published: 13 Jun 2016 501 ZRC Zoological Reference Collection, Lee Kong Chian Natural History Museum, National University of Singapore (Singapore) Material was studied with binocular microscopes Measurements were mainly made with a stage micrometre attached to oculars of the microscopes Lengths of body segments (thoracic or abdominal) are measured along the midline All measurements are given in millimetres Line drawings were made with the help of a camera lucida fixed to the microscopes Some habitus illustrations were taken with a digital SLR camera using macro lenses Taxonomy Rhyacobates Esaki, 1923 Rhyacobates Esaki, 1923: 387 (type species: Rhyacobates takahashii Esaki, 1923); Hungerford & Matsuda, 1960: (key to genus); Matsuda, 1960: 273–276 Esakobates Lundblad, 1934: 22 (type species: Esakobates svenhedini Lundblad, 1934); (synonymized by Hungerford & Matsuda, 1959: 69) Key to species of Rhyacobates occurring in Vietnam - - Both sexes: mesonotum totally black, without yellow marking Female: abdominal sternum without connexival process, connexival and posterolateral margins expanded, folded inwards and covering dorsum of genitalia (Figs 34–39) R constrictus sp.n Both sexes: mesonotum with median yellow marking Female: abdominal sternum with connexival process, connexival and posterolateral margins not modified as above Male: mesonotum with slender yellow median stripe only on posterior half Female: posterior margin of metanotum with a conspicuous median process; abdomen short, ventral length of abdomen about 0.2 times body length R anderseni Male: mesonotum with yellow median marking distinctly longer than half the length of mesonotum Female: metanotum without median process; abdomen longer, ventral length of abdomen about 0.4–0.5 times body length Body length of male at least 7.3 mm, of female at least 9.8 mm Female: tergum with median process on posterior margin Body length of male at most 7.0 mm, of female at most 10.0 mm Female: tergum with posterior margin straight, without median process Male: pronotum chiefly yellow; mesonotum with broad, sub-oval yellow median marking; metanotum with broad crownshaped yellow marking (Fig 12) Female: sternum with short connexival processes; posterior margin of sternum bilobate (Figs 21, 22) R zetteli sp.n Male: both pronotum and mesonotum with slender yellow median marking; metanotum without yellow marking Female: sternum with longer and sub-triangular connexival processes (Figs 8, 10); posterior margin of sternum without lobe, broadly convex (Fig 9) R angustus sp.n Male: yellow stripe on mesonotum about three quarters of mesonotum length, not reaching anterior margin; paramere without hook-shaped apex Female: abdomen straight, abdominal segment with two long dorsal processes, posterior ventral margin straight and without median projection R gongvo Male: yellow stripe on mesonotum almost as long as mesonotum length; paramere with hook-shaped apex Female: distal half of abdomen curved upwards; abdominal segment without long dorsal process, posterior ventral margin with small and pointed median projection R abdominalis Rhyacobates angustus sp.n (Figs 1–10) Material examined Holotype (apterous female) and allotype (apterous male),VIETNAM, Lao Cai Prov., Sa Pa, Ban Ho, Ban Den, Nam Pu stream (feeder stream of Muong Hoa stream), 22°15.709’N 103°58.054’E, 416 m asl., coll Tran A.D et al., 29 May 2013, TAD1316 (ZMHU) Paratypes: males (apterous), same locality data as holotype (ZMHU) Description Size: apterous morph, males, length 7.7–8.1 (allotype 8.0), width 2.26–2.40 (allotype 2.40); female (holotype), length 11.3, width 2.95 Colour: Dorsum of body mainly black, covered with silvery pubescence, especially on thoracic pleura, metacoxa and abdomen Dorsum of head yellow with median, longitudinal brown mark on anterior three quarters 502 · Zootaxa 4121 (5) © 2016 Magnolia Press TRAN & NGUYEN Antennae mainly black, segment with whitish area in distal two-fifths Pronotum mainly black with median yellow mark (in female, width of mark broad, about one third of pronotum mark; in male, yellow mark narrow) Mesonotum black with median yellow mark from anterior fifth to posterior margin; median mark of female broader than in male Metanotum black, in female with median yellow marking, in male without yellow mark Abdominal terga of male chiefly black or brown Abdominal terga of female mainly black or brown, with yellow connexiva Venter of body covered with silvery and golden pubescence Venter of female mainly light yellow, except mesosternum and mesopleuron black on anterior part, with sub-triangular yellow on posterior part of mesosternum Venter of male similar to female, but triangular yellow mark on mesosternum narrower, abdominal venter dark yellow All acetabulae, coxae and trochanters yellow Fore femur yellow with light brown dorsal stripe on distal part Middle and hind femora yellow-brown at basal part, dark brown or black at distal part Fore tibia yellowbrown and basal part, dark brown at distal part; other tibiae and all tarsi dark brown or black Apterous female (holotype): Body long and relatively slender Head width 1.60, interocular width 0.65, eye length (dorsal view) 0.65 Lengths of antennal segments 1–4: 4.95: 1.39: 1.54: 1.16 Pronotum broader than long, length 0.80, width 1.71; mesonotum length 2.72, width 2.72; metanotum length 0.79 Thoracic pleura with numerous long erect bristle-like black hairs, especially on mesopleuron 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: 5.10: 4.75: 2.38: 1.10; middle leg: 13.80: 7.90: 3.30: 0.47; hind leg: 13.60: 5.69: 0.18: 0.27 Fore femur slender (width 0.51), venter of femur with row of dark bristle-like hairs and scattered soft long hairs, sub-apical part slightly constricted with small tooth-like elevation (Fig 1) Abdomen prolonged, narrower than thorax, ventral length 5.38, gradually tapering towards apex (Figs 7, 8) Tergum posteromedially swollen, forming a semi-circular tumescence (Fig 8) Connexival margin of segments 1–6 thickened Abdominal segment prolonged, almost completely enclosing genital segments, tergum medially produced on posterior margin; sternum (length 1.99) about 1.8 times as long as tergum (length 1.12); connexival margin of sternum about two thirds ventral length of sternum 7; posterior margin of sternum broadly convex and thickened; each posterolateral corner of sternum with broad, sub-triangular process (Figs 8, 10) Apterous male (allotype): Head width 1.44, interocular width 0.64, eye length 0.61 Lengths of antennal segments 1–4: 4.80: 1.33: 1.48: 1.10 Pronotum broader than long, length 0.77, width 1.64; mesonotum length 2.16; metanotum length 0.68 Thoracic pleura with numerous long erect bristle-like black hairs, especially on mesopleuron Lengths of leg segments: fore leg: 4.95: 4.35: 1.30: 0.81; middle leg: 13.50: 7.20: 3.00: 0.47; hind leg: 13.25: 4.60: 0.16: 0.23 Fore femur slender (width 0.50) with few scattered soft long hairs in venter, sub-apical part with small tooth-like elevation Middle trochanter without spines, middle femur with many spines, those at basal fifth of femur not arranged in distinct row and those at distal four fifths arranged in distinct row (Fig 2) Other leg structures similar to those of female Abdomen relatively short, ventral length 3.13 Length of sternum 7: 0.31, posterior margin slightly concave Genitalia: directed slightly downwards; venter of abdominal segment length (in-situ) 0.20; proctiger laterally widened forming a rounded lobe on each side (Fig 3); pygophore of moderate size, apical margin rounded; paramere relatively long, curved at basal third, slightly thickened at middle, apex narrow and directed inwards, setae not distinct (Figs 4, 5); endosomal sclerites as in Fig Macropterous morph unknown Etymology The species epithet refers to the slender appearance of the female body Remarks Rhyacobates angustus sp.n differs from all of its congeners in the combination of following characters: the body in dorsal view is generally slender, especially in the female; the abdomen of the female is straight (Figs 7, 8); abdominal segment of the female is prolonged and in lateral view, tapers apically (Figs 8– 10), each posterolateral corner of sternum is produced into a broad, sub-triangular process (Figs 8, 10), the posterior margin of sternum is broadly convex and thickened, without a median process (Fig 9); the apex of the male paramere is curved and directed inwards (Fig 5) For comparison with its congeners, see Remarks for Rhyacobates zetteli sp.n Habitats Specimens of R angustus sp.n were found in a open mountain stream at an elevation of above ca 400 m They were found living sympatrically with R gongvo, a more common species in the area (Fig 40) After several searches and additional field trips, we could not find further specimens of this new species Therefore, we are unable to determine whether this new species is uncommon in the area or if this was an atypical habitat and it is more common elsewhere Distribution Vietnam: Lao Cai NEW RHYACOBATES FROM VIETNAM Zootaxa 4121 (5) © 2016 Magnolia Press · 503 FIGURES 1–10 Morphological features of Rhyacobates angustus sp.n (1) right fore leg of female (2) basal part of right middle leg of male, ventral view (3) proctiger of male (4, 5) left paramere, from different views (6) endosomal sclerites (7) body of female, lateral view (8) abdomen of female, dorsal view, (9, 10) apex of abdomen of female, ventral and lateral views 504 · Zootaxa 4121 (5) © 2016 Magnolia Press TRAN & NGUYEN Rhyacobates zetteli sp.n (Figs 12–23) Material examined Holotype (apterous female) and allotype (apterous male), Vietnam, Lao Cai Prov., Sa Pa, Hoang Lien N'Park, Nui Xe, Suoi Vang, 22°20.835’N 103°46.446’E, 1366 m asl., coll Tran A.D., July 2004, TAD0417 (ZMHU) Paratypes: VIETNAM: Lao Cai Prov.: 11 males, 13 females (apterous), same locality data as holotype (ZMHU, ZRC, NHMW); female (macropterous, de-alated), Sa Pa, Hoang Lien N'Park, Nui Xe, a small water flow, 22°21.110’N 103°46.216’E, 1978 m asl., coll Tran A.D., July 2004, TAD0418 (ZRC); female (apterous), Sa Pa, Nui Xe, Tram Ton area, feeder stream of Vang stream, 22°20.020’N 103°46.223’E, 1904 m als., coll Tran A.D et al., 25 October 2013, TAD1357 (ZMHU) Description Size: males (apterous), length 7.30–7.70 (allotype 7.55), width 2.44–2.67 (allotype 2.54); females, length 9.8–10.6 (holotype 10.5), width 3.04–3.58 (holotype 3.41) (apterous), length 10.3, width 3.36 (macropterous, de-alated) Colour (Figs 12, 13): Dorsum of body mainly black or brown, covered with golden and silvery pubescence Head yellow with (male) or (female) small black markings dorsally Antennae mainly black, segment with whitish area in distal two-fifths Pronotum mainly yellow with black outer margin Pronotum in macropterous form (female) with black anterior margin, anterior part (before pronotal lobe) yellow, pronotal lobe black with thin longitudinal yellow stripe, lateral and posterior margins yellow Mesonotum in apterous form black with broad yellow median marking from anterior to posterior margins; median marking of females broader than in males Metanotum with expanded yellow marking (broader in females) Abdominal terga mainly black or brown, with yellow-brown connexiva Venter of female mainly light yellow, except anterior half of mesosterno-pleuron black or brown, with median light yellow marking confluent with light coloured posterior part Venter of male, mesosternopleuron mainly black or brown, with long light yellow triangular marking on posterior half, abdominal venter light yellow All coxae and trochanters yellow Fore femur yellow with light brown dorsal stripe Middle and hind femora yellow-brown at basal part, dark brown or black at distal part All tibiae and tarsi dark brown or black Apterous female (holotype): Head width 1.56, interocular width 0.76, eye length (dorsal view) 0.63 Lengths of antennal segments 1–4: 4.02: 1.08: 1.49: 1.12 Pronotum broader than long, length 0.76, width 1.86; mesonotum length 1.51, metanotum length 0.56 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: 4.48: 4.07: 2.01: 0.98; middle leg: 12.30: 7.65: 4.17: 0.46; hind leg: 12.50: 6.75: 0.22: 0.32 Fore femur slender (width 0.44), with row of 11 long dark bristle-like hairs and scattered soft long hairs on venter, sub-apical part with small tooth-like elevation (Fig 14) Abdomen (Figs 20, 21) straight, prolonged, ventral length 5.10 Connexival margin narrow Each connexival corner of segment with small blunt process (Fig 21) Abdominal segment prolonged, almost completely enclosing genital segments, tergum medially produced on posterior margin; sternum (length 1.68) slightly more than 1.5 times as long as tergum (length 1.02), posterior margin of sternum bilobate; posterolateral corner of abdominal segment with small blunt process (Figs 20, 21), sometimes bent inwards thus not visible in lateral view (Fig 23) Apterous male (allotype): Head width 1.45, interocular width 0.70, eye length 0.60 Lengths of antennal segments 1–4: 4.02: 1.06: 1.56: 1.11 Pronotum broader than long, length 0.73, width 1.68; mesonotum length 2.08, metanotum length 0.69 Lengths of leg segments: fore leg: 4.41: 3.82: 1.27: 0.91; middle leg: 12.00: 7.10: 3.72: 0.46; hind leg: 11.70: 7.55: 0.21: 0.30 Fore femur with similar pubescence as in apterous female, sub-apical part also with small tooth, width of fore femur 0.51 Middle trochanter with 6–7 spines at distal part, middle femur with spines but not in distinct row (Fig 15) Other leg structures similar to those of female Abdomen relatively short, ventral length 2.74 Length of sternum 7: 0.43, posterior margin straight Genitalia: directed slightly downwards; venter of abdominal segment length (in-situ) 0.24; proctiger relatively widened, with broadly angular lobes laterally (Fig 16); pygophore of moderate size, apical margin almost straight; paramere relatively long and slender, curved at distal two-thirds, setae not distinct (Figs 17, 18); endosomal sclerites as in Fig 19 De-alated macropterous female: Head width 1.52, interocular width 0.78, eye length 0.67 Lengths of antennal segments 1–4: 4.12: 1.11: 1.52: 1.22 Pronotum covering most of mesonotum, length 3.23, width (across humeri) 2.71; metanotum length 0.62 Lengths of leg segments: fore leg: 4.31: 4.02: 1.98: 1.03, width of fore femur 0.44; middle leg: 12.30: 7.60: 4.17: 0.48; hind leg: 12.40: 6.60: 0.21: 0.29 Other structural characteristics similar to apterous females NEW RHYACOBATES FROM VIETNAM Zootaxa 4121 (5) © 2016 Magnolia Press · 505 Macropterous male: unknown Etymology This species is dedicated to Dr Herbert Zettel (Natural History Museum Vienna) for his great contribution to the knowledge of aquatic bugs of Southeast Asia, and for enthusiastically supporting the first author in the field of water bug research FIGURES 11–13 (11) Habitat of type locality of Rhyacobates zetteli sp.n (12, 13) Habitus of R zetteli sp.n (12) apterous male (13) apterous female (photographed by Tran Anh Duc) 506 · Zootaxa 4121 (5) © 2016 Magnolia Press TRAN & NGUYEN FIGURES 14–23 Morphological features of Rhyacobates zetteli sp.n (14) right fore leg of female (15) basal part of right middle leg of male, ventral view (16) proctiger (17, 18) left paramere, two different views (19) endosomal sclerites (20) body of female, lateral view (21–23) apex of abdomen of female, dorsal, ventral, and lateral views respectively Remarks Rhyacobates zetteli sp.n differs from all of its congeners in the combination of following characters: the unique dorsal colour pattern of the body (Figs 12, 13); the abdomen of the female is straight; each connexival corner of segment has a small, blunt process (Fig 21); abdominal segment of the female is prolonged and in lateral view, tapers apically (Figs 21–23), the connexival margin of sternum is much shorter NEW RHYACOBATES FROM VIETNAM Zootaxa 4121 (5) © 2016 Magnolia Press · 507 than the ventral length (Figs 21, 23); the connexival corner of sternum of the female is produced into a small blunt process (Fig 21), the posterior margin of sternum is bilobate, but without a median process (Fig 22) The shape of the paramere of this new species is similar to that of R gongvo, but males of the latter can be separated from this new species by other characteristics, i.e., colouration, shape of the proctiger and endosomal structures Both new species, Rhyacobates angustus sp.n and R zetteli sp.n., are closely related to each other, as both taxa possess the prolonged and rather straight abdomen of the female, the posteromedian process on tergum of the female, and the sub-apical tooth-like elevation on the fore femur of the female In the subfamily Ptilomerinae, similar modification on the posterior margin of female tergum is previously known only in the genus Stridulobates Zettel & Thirumalai, 2001a (see Zettel & Thirumalai 2001a: Figs 15, 16) However, in species of Stridulobates, tergum of the female is prolonged and covers most of tergum 8, whereas in R angustus sp.n and R zetteli sp.n., tergum is shorter and covers only a small anterior portion of tergum Other characteristics, e.g., the absence of a metanotal process in females, the lack of a "stridulatory device" on the middle trochanter and sterna 2–6 in males, also suggests that R angustus sp.n and R zetteli sp.n not belong to Stridulobates Additionally, males of R angustus sp.n and R zetteli sp.n clearly differ from males of Stridulobates in the shape of the parameres and structure of endosoma (see Matsuda 1960: Figs 677, 679; Zettel & Thirumalai 2001a: Figs 9, 10) Rhyacobates angustus sp.n and R zetteli sp.n can be easily separated from each other by the yellow median markings on the nota, the shape of the male proctiger and paramere, and the structures of female sternum In R angustus sp.n., yellow markings on the pro- and mesonota are slender (the metanotum of the male is totally black and without yellow marking, the metanotum of the female is with very slender with a yellow median marking; the male proctiger has a rounded lobe on each side) (Fig 3); the apex of the male paramere is more abruptly narrowed (Figs 4, 5), sternum of the female has large, sub-triangular connexival processes and a broadly-arched posterior margin (Figs 8–10) In R zetteli sp.n., yellow markings on the nota of both sexes are broad; the male proctiger has a broadly angular lobe on each side; the male paramere gradually tapers apically (Figs 17, 18); sternum of the female has small blunt connexival processes (Fig 21), the posterior margin of sternum is bilobate (Fig 22) Habitats Most specimens of Rhyacobates zetteli sp.n were collected in a shaded and fast flowing mountain stream at an elevation of over 1800 m (Fig 11) They were found skating in schools of numerous individuals: adults and nymphs in a mixture of which the nymphs were predominant Seasonal fluctuation in population size and ratios of nymphs to adults are still unknown The individuals of this species were also found often resting on partially submerged rocks in the middle the stream, as other species of Rhyacobates (Esaki 1923; Tran & Yang 2006) One macropterous specimen (with a de-alated wing) was found in an unshaded, tiny water flow (locality TAD0418), which continues underground and was ca 500 m from the main stream (locality TAD0417) None of the specimens found in the main stream were the macropterous form This observation suggests that this species has good flying ability (probably for dispersal), but upon migrating, the macropterous individuals were likely to have their wings broken off Distribution Vietnam: Lao Cai 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., June 2013, TAD1331 (ZMHU) Paratypes: VIETNAM: Phu Tho Prov.: males, females (apterous), female (macropterous, de-alated), same locality data as holotype (ZMHU, ZRC); males, 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., June 2013, TAD1332 (ZMHU); 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., June 2013, TAD1333 (ZMHU); 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); females (apterous), Xuan Son N’Park, Lap stream, site 1, at Ngoc waterfall, coll Tran A.D et al., 30 August 2013, 508 · Zootaxa 4121 (5) © 2016 Magnolia Press TRAN & NGUYEN TAD1352 (GPS data same as TAD1331) (ZMHU); males, 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); males, 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); males, 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); males, 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); male, 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); 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 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 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 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 posteromedially swollen (Figs 36) Connexival margin of segments 1–5 narrow, of segment thickened Abdominal segment prolonged, completely enclosing genital segments, tergum short (length 0.45), posterior part thickened, medially notched on posterior margin; sternum (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 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 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 NEW RHYACOBATES FROM VIETNAM Zootaxa 4121 (5) © 2016 Magnolia Press · 509 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) 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 of the female, which holds genital segments within 510 · Zootaxa 4121 (5) © 2016 Magnolia Press TRAN & NGUYEN 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 NEW RHYACOBATES FROM VIETNAM Zootaxa 4121 (5) © 2016 Magnolia Press · 511 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 expand dorsad and fold inwards; thus, sternum covers most of the genital segments (Figs 35–39), sternum 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 of the female is unique for R constrictus sp.n The median process on sternum 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 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 Rhyacobates abdominalis Andersen & Chen, 1995 Rhyacobates abdominalis Andersen & Chen, 1995: 58–59, Figs 12–15 (type locality: Ruyang Nat Res., Guangdong Prov., China); Tran & Yang, 2006: 19 (record Vietnam) Material examined Paratypes: male, female (apterous), “China: Guangdong Prov., Ruyang Nat Res., Lao Peng Keng stream, 1100m, 14.8.1990, coll P.P Chen, C9012” (NHMW) For formerly examined specimens (from Vietnam), see Tran & Yang (2006) Size Males, length 6.8–7.0, width 2.10–2.20 (apterous), length 6.4–6.6, width 2.06–2.11 (macropterous, dealated); females, length 9.9–10.0, width 3.50 (apterous), length 9.4–9.6, width 3.14–3.30 (macropterous, dealated) Remarks Rhyacobates abdominalis can be recognised by the following diagnostic characters: abdominal segment of the male is ventrolaterally impressed; the proctiger of the male has a small angular projection on each side; the male paramere is slender with a broad basal part and hook-shaped apex (see Andersen & Chen 1995: Fig 15); the abdomen of the female is distinctly curved dorsad, abdominal segment possesses a short projection on each connexivum, and the posterior margin of sternum has a sharp, small median process (see Andersen & Chen 1995: Figs 12–14) The specimens of R abdominalis from Vietnam were not significantly different compared to the paratypes from China, except for the larger size and less pointed median process of sternum in the female They were collected from the same habitat as Rhyacobates gongvo For description notes of Vietnamese specimens, see Tran & Yang (2006: 19) Habitats See Tran & Yang (2006: 18, 19) Distribution Vietnam: Lao Cai China: Guangdong Rhyacobates anderseni Tran & Yang, 2006 Rhyacobates anderseni Tran & Yang, 2006: 14–16, Figs 7–16, 27 (type locality: Vu Quang, Ha Tinh Prov., Vietnam) Material examined For holotype and paratypes, see Tran & Yang (2006) Size Males, length 6.0–6.1 (allotype 6.0), width 1.83–1.85 (allotype 1.83) (apterous), length 6.1–6.2, width 1.85–1.88 (macropterous); females, length 6.8–7.0 (holotype 6.8), width 2.52–2.57 (holotype 2.52) (apterous) 512 · Zootaxa 4121 (5) © 2016 Magnolia Press TRAN & NGUYEN Remarks The followings are diagnostic characteristics of R anderseni: the mesonotum of the male has a slender yellow stripe on the posterior half; the mesonotum of the female has a broader yellow median marking on the posterior three-fifths; the abdomen of the male is relatively short; in lateral view, abdominal segment of the male has a concave ventral surface; the male proctiger has round angular projections on each side (see Tran & Yang 2006: Fig 12); the male paramere is falciform, slightly broad, long, and not conspicuously setose (see Tran & Yang 2006: Figs 13, 14); the metanotum of the female has a pointed median process on the posterior margin (see Tran & Yang 2006: Fig 7); the abdomen of the female is short (length about 0.2 times body length), sternum is long, almost enclosing the genital segments with its connexival margin raised slightly upwards, with a pair of long posterior projections pointing outwards and downwards (see Tran & Yang 2006: Figs 8, 9), and its posterior margin is almost straight, bearing two short lateral processes (see Tran & Yang 2006: Fig 10) For detailed comparisons of Rhyacobates anderseni with its congeners and other ptilomerine genera (Andersenius and Pleciobates), refer to Tran & Yang (2006: 16) Habitats See Tran & Yang (2006: 16) Distribution Vietnam: Ha Tinh China: Yunnan Rhyacobates gongvo Tran & Yang, 2006 (Figs 41, 42) Rhyacobates gongvo Tran & Yang, 2006: 16–19, Figs 17–25, 28 (type locality: Sa Pa, Lao Cai Prov., Vietnam) Material examined For holotype and paratypes, see Tran & Yang (2006) Others: VIETNAM: Lao Cai Prov.: female (apterous), Sa Pa, Nam Sai, Seo Nam Sai stream 1, 22°15.761’N 103°55.909’E, 844 m asl., coll Dinh N.H et al., 24 October 2012, DNH12.09 (ZMHU); female (apterous), Sa Pa, Nam Sai, Seo Nam Sai stream 2, 22°14.67’N 103°59.541’E, 469 m asl., coll Dinh N.H et al., 24 October 2012, DNH12.10 (ZNHU); males, females (apterous), males (macropterous, de-alated), Sa Pa, Ban Ho, Ban Den, Nam Pu stream (feeder stream of Muong Hoa stream), 22°15.709’N 103°58.054’E, 416 m asl., coll Tran A.D et al., 29 May 2013, TAD1316 (ZMHU); male, females (apterous), Sa Pa, Thanh Phu, Nam Cang stream, 22°15.401’N 103°58.866’E, 398 m asl., coll Tran A.D et al., 26 October 2013, TAD1359 (ZMHU); 13 males, females (apterous), Sa Pa, Ban Ho, Nam Pu stream (feeder stream of Muong Hoa stream), site 1, at lower section, 22°15.778’N 103°58.270’E, 404 m asl., coll Tran A.D et al., 26 October 2013, TAD1361 (ZMHU); female (apterous), Sa Pa, Cat Cat, Ho stream (feeder stream of Muong Hoa stream), 22°19.546’N 103°49.880’E, 1233 m asl., coll Tran A.D et al., 27 October 2013, TAD1366 (ZMHU) Size Males, length 6.2–6.5 (allotype 6.5), width 1.88–2.20 (apterous), length 6.4, width 1.97 (macropterous, de-alated); females, length 7.8–8.3 (holotype 8.3), width 2.52–2.67 (holotype 2.52) (apterous), length 7.5, width 2.44 (macropterous, de-alated) Remarks Rhyacobates gongvo differs from other species of Rhyacobates by the following diagnostic characteristics: in the apterous morph, the mesonotum has a median yellow stripe on the posterior three quarters; the male proctiger has small angular projections on each side (see Tran & Yang 2006: Fig 22); the male paramere is relatively long and slender, not setose (see Tran & Yang 2006: Figs 24, 25); the abdomen of the female is elongate and straight (length about 0.4 times body length), the posterior part of sternum is slightly depressed dorsoventrally (see Tran & Yang 2006: Fig 17); sternum of the female does not totally enclose the genital segments, the posterior margin is straight and without a process, and the connexival projections are long, straight, and flat (see Tran & Yang 2006: Figs 18–20) Rhyacobates gongvo is relatively similar to R malaisei Andersen & Chen, 1995, but can be separated from the latter by the diagnosis above (for a comparison between these two species, see Tran & Yang 2006: 18–19) Habitats See Fig 40; also see Tran & Yang (2006: 18) Distribution Vietnam: Lao Cai NEW RHYACOBATES FROM VIETNAM Zootaxa 4121 (5) © 2016 Magnolia Press · 513 FIGURES 40–42 (40) Habitat of Rhyacobates angustus sp.n and R gongvo (41) Apterous female of R gongvo resting on the exposed rock in the middle of the stream (42) School of adults and nymphs of R gongvo on the exposed rock in the middle of the stream (40: photographed by Nguyen Thanh Son; 41, 42: photographed by Tran Anh Duc) 514 · Zootaxa 4121 (5) © 2016 Magnolia Press TRAN & NGUYEN Discussion Andersen & Chen (1995) determined that the characteristics of abdominal segment of the female (tube-like, prolonged, and completely enclosing genital segments) as one of the generic diagnostic features of Rhyacobates This character state is not totally true in R anderseni and R gongvo; they are tube-like and prolonged but not completely enclosing the genital segments (see Remarks for each species, also see Tran & Yang 2006: 16, 18, 19) Additionally, females of R anderseni have a short median process on posterior margin of metanotum Although Andersen & Chen (1995) did not include the absence of a metanotal process as a generic character of Rhyacobates, it is not present in any other species of Rhyacobates Note that the short metanotal process is present in other ptilomerine genera, i.e., Pleciobates Esaki, Stridulobates Zettel & Thirumalai Another ptilomerine species, Jucundus custodiendus Distant, 1910 also possesses a metanotal process, but this structure is very long and slender in this species (see Zettel & Thirumalai 2001b: Fig 1) However, R anderseni and R gongvo match all other diagnostic characters of Rhyacobates (see Andersen & Chen 1995: 54) A similar situation occurs in Rhyacobates angustus sp.n and R zetteli sp.n., as they both have a posteromedian process on tergum of the female, a character previously known only in species of Stridulobates (see Remarks for R zetteli sp.n.), but both agree well with other diagnostic characters of Rhyacobates Thus, in this study, Rhyacobates is accepted at a slightly wider sense than the generic definition by Andersen & Chen (1995) In previous studies, Andersen & Chen (1995), Polhemus & Zettel (1997), Zettel & Thirumalai (2001a, b), Chen et al (2005), and Zettel (2009) suggested a comprehensive phylogenetic analysis of the subfamily Ptilomerinae Until such analysis becomes available, any judgement of the characters mentioned above (metanotal process in females of R anderseni, median process of tergum in females of R angustus sp.n and R zetteli sp.n.) in relation to respective ptilomerine taxa is very speculative Regarding the habitats and behaviour of Rhyacobates, Esaki (1923: 389) noted that individuals of R takahashii “glide swiftly on the surface of water” and are “hardly recognisable owing to the disturbance of the water” Individuals of Rhyacobates have silvery pubescence on body surface, making their body merge well with the reflective, turbulent surface of stream currents Our observation on Rhyacobates from Vietnam agrees with Esaki’s (1923) findings We also found that they usually rest near the water margin on exposed rocks in the middle of the stream (Figs 26, 41, 42) They are very cautious, so they quickly jump off the rocks and skate away when disturbed We were able to photograph them in their resting place only when we approached carefully and slowly, without any sudden movement Thus, locomotory behaviour of this group probably contributes to their being overlooked during collection trips, and the true species diversity of Rhyacobates might be much higher than what is currently recorded Acknowledgements We sincerely thank Mr Nguyen Thanh Son (Hanoi University of Science, Vietnam) for some additional specimens of Rhyacobates constrictus and for advice on taking in-situ photographs of small, reflective and fast moving striders like Rhyacobates; Dr Nguyen Van Vinh (Hanoi University of Science, Vietnam) and Mr Nguyen Van Hieu (Hanoi Pedagogical University 2, Vietnam) for assistance during fieldwork We also grateful to Dr Herbert Zettel (Natural History Museum, Vienna, Austria), Dr Robert W Sites (University of Missouri, USA), and an anonymous reviewer for their critical reviews and useful suggestions to improve the manuscript This research is funded by Vietnam National Foundation for Science and Technology Development (NAFOSTED) under grant number 106.15-2012.69 References Andersen, N.M & Chen, P.-P (1995) A taxonomic revision of the Ptilomerine genus Rhyacobates Esaki (Hemiptera: Gerridae), with five new species from China and adjacent countries Tijdschrift voor Entomologie, 138, 51–67 Chen, P-P., Nieser, N & Zettel, H (2005) The aquatic and semi-aquatic bugs (Heteroptera: Nepomorpha & Gerromorpha) of Malesia Fauna Malesiana Handbooks Brill, Leiden,/Boston, 546 pp Distant, W.L (1910) Some undescribed Gerrinae Annals and Magazine of Natural History, Series 8, 5, 140–153 NEW RHYACOBATES FROM VIETNAM Zootaxa 4121 (5) © 2016 Magnolia Press · 515 Esaki, T (1923) An interesting new water strider from Formosa The Philippine Journal of Science, 22 (4), 387–392 Hungerford, H.B & Matsuda, R (1959) Synonymy of the genera Rhyacobates Esaki, 1923 and Esakobates Lundblad, 1934, and a description of a new species of Rhyacobates from China (Hemiptera: Gerridae) Journal of the Kansas Entomological Society, 32 (1), 67–92 Hungerford, H.B & Matsuda, R (1960) Key to subfamilies, tribes, genera and subgenera of the Gerridae of the world Kansas University Science Bulletin, 41 (1), 2–23 Lundblad, O.M (1934) Schwedisch-chinesische wissenschafliche Expedition nach den nordwestlichen Provinzen Chinas 28 Hemiptera Wasserhemipteren Arkiv för Zoologi, 27A (14), 1–31 Matsuda, R (1960) Morphology, evolution and a classification of the Gerridae (Hemiptera-Heteroptera) The University of Kansas Science Bulletin, 41 (2), 25–632 http://dx.doi.org/10.5962/bhl.part.15602 Miyamoto, S (1967) Gerridae of Thailand and North Borneo taken by the joint Thai-Japanese Biological Expedition 1961-62 Nature and Life in Southeast Asia, 5, 217–257 Polhemus, J.T & Zettel, H (1997) Five new Potamometropsis species (Insecta: Heteroptera: Gerridae) from Borneo Annalen des Naturhistorischen Museums in Wien, 99B, 21–40 Tran, A.D & Yang, C.M (2006) New species of the water strider genera Eotrechus Kirkaldy and Rhyacobates Esaki (Heteroptera: Gerridae) from Vietnam Raffles Bulletin of Zoology, 54 (1), 11–20 Zettel, H (2009) Three new genera of Ptilomerinae (Hemiptera: Heteroptera: Gerridae) from Southeast Asia Zootaxa, 2046, 26–42 Zettel, H & Thirumalai, G (2001a) Stridulobates anderseni, a new genus and species of ptilomerine Gerridae (Hemiptera: Heteroptera) with 'stridulatory devices' from South India Insect Systematics and Evolution, 31, 433–439 http://dx.doi.org/10.1163/187631200X00462 Zettel, H & Thirumalai, G (2001b) Re-establishment of the ptilomerine genus Jucundus Distant, 1910 (Insecta: Heteroptera: Gerridae), with redescription of the type species Jucundus custodiendus Distant, 1910 from South India and notes on J vittatus (Esaki, 1928) comb.n from Sri Lanka Annalen des Naturhistorischen Museums in Wien, 103B, 273–282 516 · Zootaxa 4121 (5) © 2016 Magnolia Press TRAN & NGUYEN ... 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... (Fig 22) The shape of the paramere of this new species is similar to that of R gongvo, but males of the latter can be separated from this new species by other characteristics, i.e., colouration,... Magazine of Natural History, Series 8, 5, 140–153 NEW RHYACOBATES FROM VIETNAM Zootaxa 4121 (5) © 2016 Magnolia Press · 515 Esaki, T (1923) An interesting new water strider from Formosa The Philippine