Revised key to species of Rhyacobates Esaki, 1923 Note: The males of Rhyacobates spp. do not exhibit many reliable characters for species identification. In most species, the shape of the proctiger, especially its lateral lobes, and the shape of the paramere, preferably to be used in combination, are the only characters for species identification. However, species identification of Rhyacobates are more reliable when associated female specimens are present in the samples. 1. Both sexes: both mesonotum and metanotum completely black, without median yellow marking (Figs 3A–B, 4A–B) ........................................................................................................................... 2 – Both sexes: mesonotum with median yellow marking (Figs 3C–R, 4C–M, O) ............................... 4 2. Female: body relatively robust, width 3.1–3.2, ratio of body width: length> 0.36; abdominal mediotergite I swollen, nearly as long as two posterior terga together (Fig. 3I); posterior margin of abdominal mediotergite VII without median process; posterior margin of abdominal segment VII dorsally without process, ventrally with a narrow median process (Fig.5H). Male: middle trochanter without spines; lateral lobes of proctiger distinctly angular (Fig. 6H); paramere strongly thickened at middle, with scattered short setae on distal part ....................... R. constrictus Tran & Nguyen, 2016 – Female: body relatively slender, width 2.3–3.0, ratio of body width: length <0.29; abdominal mediotergite I not swollen, nearly as long as mediotergite II; posterior margin of abdominal mediotergite VII with a median process; posterior margin of abdominal segment VII dorsally with a pair of processes, ventrally with a semicircular median process (Figs 16E, 18E). Male: middle trochanter with 3–5 spines (Figs 16J, 17I); lateral lobes of proctiger subtrapezoid or broadly rounded (Fig. 6A–B); paramere not thickened at middle, distal part without setae (Fig. 8A–B) .................. 3 3. Female: body length 8.8–9.3, connexival process of abdominal segment VII short, with relatively blunt apex (Fig. 16D). Male: body length 6.5–6.9; lateral lobes of proctiger subtrapezoid (Fig. 6A); apical part of paramere relatively slender, distinctly curved (Figs 8A, 16L) .............. R. bui sp. nov. – Female: body length 11.2–11.9, connexival process of abdominal segment VII long, with pointed apex (Fig. 18D). Male: body length 7.7–8.0; lateral lobes of proctiger broadly rounded (Fig. 6B); apical part of paramere relatively stout, not distinctly curved (Figs 8B, 18K) .................................. ........................................................................................................................... R. elongatus sp. nov. 4. Female: metanotum completely black, without yellow markings (Fig. 3F, K, M). Male: length of middle tibia ca 1.8–2.1 times length of hind tibia ............................................................................ 5 – Female: metanotum with median yellow stripe. Male: length of middle tibia usually less than 1.8 times length of hind tibia (except in R. edentatus: 1.9–2.0, and R. takahashii: 1.5–1.8) ................. 7 5. Female: posterior margin of metanotum with a pointed median process (Fig. 23C–D); abdomen short, ventral length ca 0.2 times body length; posterior margin of abdominal segment VII with long connexival processes and laterally with a pair of pointed processes (Fig. 23F, H). Male: ventral length of abdomen ca 0.3 times body length; lateral lobes of proctiger rounded; paramere stout, with middle part thickened (Figs 8E, 23M) ............................................ R. anderseni Tran & Yang, 2006 – Female: posterior margin of metanotum without process; abdomen longer, ventral length ca 0.5 times body length; posterior margin of abdominal segment VII with long connexival processes and laterally with a pair of short angular processes or without distinct process (Figs 5J, L, 30F–G). Male: ventral length of abdomen ca 0.4–0.5 times body length; lateral lobes of proctiger angular; paramere slender ............................................................................................................................................... 6 6. Female: abdominal segment VII with connexiva reaching or overlapping each other on dorsum, thus covering most of mediotergites VII and VIII; posterior margin of segment VII with a pair of pointed lateral processes (Figs 3M, 30G). Male: metanotum chiefly black, without yellow markings; proctiger laterally with angular lobes produced into distinct process directed postero-ventrad (Figs 7C, 30K) ................................................................................................... R. malaisei Andersen & Chen, 1995 – Female: abdominal segment VII with connexiva not reaching each other on dorsum, thus mediotergites VII and VIII exposed; posterior margin of segment VII without distinct lateral processes (Fig. 3K). Male: metanotum with a very thin yellow median stripe; lateral lobes of proctiger angular but without distinct process (Fig. 7A) .................................................................... R. gongvo Tran & Yang, 2006 7. Female: abdominal segment VII without any posterior processes; connexiva of segments IV–VII meeting each other along midline of dorsum; posterior margin of sternum VII relatively obtuse, without distinct process (Fig. 28D–E). Male: length of middle tibia ca 1.9–2.0 times length of hind tibia .......................................................................................... R. edentatus Andersen &Chen, 1995 – Female: abdominal segment VII with posterior processes; connexiva converging and partly meeting each other at segment VII or not meeting each other; posterior margin of sternum VII ventrally with distinct process or presenting an arc shape (R. angustus). Male: length of middle tibia ≤ 1.8 times length of hind tibia ............................................................................................................................ 8 8. Both sexes: pronotum chiefly yellowish, mesonotum with a broad yellowish median marking; metanotum with laterally expanded yellow marking (Fig. 3R). Female: abdominal segment VI with small but distinct connexival processes; segment VII also with a pair small connexival processes, ventral margin bilobate. Male: lateral lobes of proctiger subtrapezoidal (Fig. 7H) ........................... ........................................................................................................... R. zetteli Tran & Nguyen, 2016 – Both sexes: pronotum, mesonotum, metanotum chiefly black, with a narrower median marking. Female: abdominal segment VI without connexival processes; ventral margin of segment VII not bilobate. Male: lateral lobes of proctiger rounded or angular .......................................................... 9 9. Female: abdominal segment VII without connexival processes (Figs 20E, G, 31E–F); abdominal mediotergite I elongate, not shorter than two subsequent terga together. Male: body length 5.4–6.3 ......................................................................................................................................................... 10 – Female: abdominal segment VII with connexival processes; abdominal mediotergite I not elongate, nearly as long as mediotergite II. Male: body length 6.2–8.4 .........................................................11 10. Both sexes: abdominal mediotergite I swollen and large, nearly as long as three subsequent terga together (Fig. 20A, H). Female: abdominal mediotergite II medially hidden beneath mediotergite I except laterally; abdominal terga II–V extremely short; abdominal segment VII as in Fig. 20E–G. Male: body length 5.9–6.3 ................................................................................... R. turgidus sp. nov. – Both sexes: abdominal mediotergite I shorter than two subsequent abdominal mediotergites together (Fig. 31A, G). Female: abdominal mediotergite II not covered by mediotergite I; terga II–V normal sized, not shortened (Fig. 31A); abdominal segment VII as in Fig. 31D–F. Male: body length 5.4– 5.9 ............................................................................................. R. recurvus Andersen & Chen, 1995 11. Female: posterior margin of abdominal sternum VII with an acute median process. Male: body length 6.2–7.4 ................................................................................................................................. 12 – Female: posterior margin of abdominal sternum VII with an obtuse median process or presenting an arc shape. Male: body length 7.5–8.4 ............................................................................................. 14 12. Female: posterior margin of abdominal mediotergite VII with a short median process (Fig. 35E); connexival processes of abdominal segment VII long and directed postero-ventrad (Fig. 35E–G). Male: lateral lobes of proctiger rounded (Figs 7G, 35M); paramere strongly curved at basal fourth as in Figs 8M, 35N, relatively straight on apical half .................................... R. takahashii Esaki, 1923 – Female: posterior margin of abdominal mediotergite VII without median process; connexival processes of abdominal segment VII short, angular, directing upwards (Figs. 22E, 25G–I). Male: lateral lobes of proctiger angular; paramere more curved on apical half ....................................... 13 13. Female: posterior margin of abdominal segment VII laterally with a pair of rounded process (Fig. 22D–E). Male: middle trochanter without spines; paramere strongly curved at basal third, as in Figs 8D, 22K ....................................................................... R. abdominalis Andersen & Chen, 1995 – Female: posterior margin of abdominal segment VII with laterally with a pair of long, pointed processes (Fig. 25E–J). Male: middle trochanter with 3–6 spines; paramere sinuate, as in Figs 8F, 25N ................................................................................. R. chinensis Hungerford & Matsuda, 1959 14. Female: connexival processes of abdominal segment VII distinctly bilobate; posterior margin of abdominal mediotergite VII with a short median process. Male: posterior lobes of proctiger angular (Fig. 7B, F) ..................................................................................................................................... 15 – Female: connexival processes of abdominal segment VII angular, not bilobate; posterior margin of abdominal mediotergite VII without median process. Male: posterior lobes of proctiger rounded (Fig. 7E) .......................................................................................................................................... 16 15. Female: subtriangular yellowish marking on metanotum wide, with larger apex angle; inner lobe of bilobate connexival processes of abdominal segment VII elongate (Fig. 29D, F). Male: paramere sinuate (Figs 8H, 29L) .................................................................... R. lundbladi (Hungerford, 1957) – Female: subtriangular yellowish marking on metanotum relatively thin, with sharp apex angle; inner lobe of bilobate connexival processes of abdominal segment VII very short (Fig. 34D–E). Male: paramere strongly curved at basal third, with hook-shaped apex (Figs 8L, 34L) .............................. .......................................................................................................... R. svenhedini (Lundblad, 1934) 16. Female: posterior margin of mediotergite VII with a median process; abdominal sternum VII with broadly rounded posterior margin (Fig. 3G); mesosternum anteriorly blackish with subtriangular yellow marking on posterior part, not divided by a blackish line. Male: middle trochanter without spines; paramere strongly curved at basal third, with narrow apex .................................................... ...................................................................................................... R. angustus Tran & Nguyen, 2016 – Female: mediotergite VII without median process; posterior margin of sternum VII angularly produced in the middle (Fig. 33D–G); mesosternum chiefly blackish with two median yellowish spots, divided by a blackish line (Fig. 33B). Male: middle trochanter with 3–5 spines; paramere strongly curved at basal fourth, with hook-shaped apex (Figs 8K, 33L) ........................................... ..................................................................................................... R. scorpio Andersen & Chen, 1995 Checklist of the genus Rhyacobates Esaki, 1923 Rhyacobates abdominalis Andersen & Chen, 1995 Rhyacobates anderseni Tran & Yang, 2006 Rhyacobates angustus Tran & Nguyen, 2016 Rhyacobates bui Leng, Tran & Ye sp. nov. Rhyacobates chinensis Hungerford & Matsuda, 1959 Rhyacobates constrictus Tran & Nguyen, 2016 Rhyacobates edentatus Andersen &Chen, 1995 Rhyacobates elongatus Leng, Tran & Ye sp. nov. Rhyacobates gongvo Tran & Yang, 2006 Rhyacobates lundbladi (Hungerford, 1957) Rhyacobates malaisei Andersen & Chen, 1995 Rhyacobates recurvus Andersen & Chen, 1995 Rhyacobates scorpio Andersen & Chen, 1995 Rhyacobates svenhedini (Lundblad, 1934) Rhyacobates takahashii Esaki, 1923 Rhyacobates turgidus Leng, Tran & Ye sp. nov. Rhyacobates zetteli Tran & Nguyen, 2016

Published as part of Leng, Zhaoqi, Tran, Anh Duc & Ye, Zhen, 2023, Taxonomic review of Rhyacobates Esaki, 1923, with descriptions of three new species (Hemiptera: Heteroptera: Gerridae), pp. 1-73 in European Journal of Taxonomy 893 (1) on pages 67-70, DOI: 10.5852/ejt.2023.893.2285, http://zenodo.org/record/8385630