Rhyacobates takahashii Esaki, 1923

Leng, Zhaoqi, Tran, Anh Duc & Ye, Zhen, 2023, Taxonomic review of Rhyacobates Esaki, 1923, with descriptions of three new species (Hemiptera: Heteroptera: Gerridae), European Journal of Taxonomy 893 (1), pp. 1-73 : 63-66

Rhyacobates takahashii Esaki, 1923

Figs 2F , 3Q , 4O , 5P , 7G , 8M , 35

Rhyacobates takahashii Esaki, 1923: 388 , pl. 1 (original description).

Rhyacobates takahashii – Esaki 1925: 60. — Matsuda 1960: 273–276, figs 656–658, 660, 663, 674–676, 678. — Andersen & Chen 1995: 55, figs 2–5 (with remarks).

Diagnosis

Body length of apterous females 8.60–10.88, of apterous males 6.20–7.32. Female: pronotum mainly black with a median brownish-yellow spot; mesonotum and metanotum mainly black with a median brownish-yellow stripe ( Fig. 35A ); posterior margin of abdominal mediotergite VII with a short median process ( Fig. 35E ); posterior margin of abdominal segment VII with three processes, including a relatively slender, angular process terminating each connexivum, and a pointed median process ventrally ( Fig. 35F–G ). Male: middle trochanter with one spine; middle femur with scattered small spines, not arranged in distinct row ( Fig. 35L ); length of middle tibia ca 1.5–1.8 times length of hind tibia; proctiger with angular lobes laterally ( Figs 7G , 35M ); paramere relatively slender, strongly curved at basal fourth, distal part tapering towards hook-shaped apex ( Figs 8M , 35N ).

Material examined

Non-type specimens

CHINA – Guangxi Province • 5 ♁♁, 2 ♀♀ (apterous); Lai-bin City, Jin-xiu County; 23°55′51.6″ N, 110°10′46.6″ E; 524 m a.s.l.; 26 Jul. 2019; Ze-zhong Jin leg.; NKUM. – Taiwan Island • 1 ♁ (apterous); Taitung, Xinwulixi, Xinwuli bridge; 2 Dec. 2001; H.H. Tan, K. Lim and Y.M. Ju leg.; THH0199; ZRC • 1 ♀ (apterous); Taipei County, Wulai, Fusan ; 24°46.973′ N, 121°30.106′ E; 336 m a.s.l.; 6 Apr. 2004; A.D. Tran leg.; TAD0402; ZRC • 3 ♁♁, 7 ♀♀ (apterous); Pingtung County, Henchun, Wangsha stream; 22°02.351′ N, 120°45.852′ E; 39 m a.s.l.; 8 Apr. 2004; A.D. Tran leg.; TAD0406; ZRC • 4 ♁♁, 2 ♀♀ (apterous), 2 ♁♁, 1 ♀ (macropterous); Yilan County, Yuanshan, Dahu stream; 24°45.218′ N, 121°39.777′ E; 147 m a.s.l.; 12 Apr. 2004; A.D. Tran leg.; TAD0412; ZRC • 7 ♁♁, 9 ♀♀ (dealated macropterous); Taizhong City, Ba-xian Mountain ; 24°17′55.1″ N, 120°45′41.5″ E; 5 Jun. 2011; Qiang Xie leg.; NKUM .

Supplemental description

Apterous female

MEASUREMENTS. Body length 8.60–10.88, width 2.59–2.90, head width 1.84, interocular width 0.85, eye length (dorsal view) 0.68; relative lengths of antennal segments I–IV: 4.10: 1.05:1.22:0.81; pronotum: length 0.90, width 1.84;mesonotum: length3.05,width 2.94; metanotum:length 0.92, width 2.65;abdomen length (ventral view) 4.66; abdominal sternum VII: length 1.87, width 1.29; abdominal mediotergite I: length 0.35, width 1.11; relative lengths of leg segments (femur:tibia:tarsal segment I:tarsal segment II): fore leg: 4.46: 3.62: 2.01:0.90, middle leg: 12.40:6.86: 2.98: 0.38, hind leg: 12.73: 4.57:0.11:0.14.

C OLORATION. Median black spot of head posteriorly bifurcate. Pronotum mainly black with a median brownish-yellow spot. Mesonotum and metanotum mainly black with a median brownish-yellow stripe ( Fig. 35A ). Abdominal tergum I with a median yellow marking. Connexivum dorsally brownish-yellow. Mesosternum chiefly blackish with a median subtriangular yellowish spot ( Fig. 35B ). Abdominal venter light yellow.

ABDOMEN. Abdomen relatively short, curved dorsad towards end ( Fig. 35D ) or nearly straight. Connexiva erect on abdominal segments I–II, converging along dorsal midline of IV–VI segments, meeting erectly above terminal mediotergites ( Fig. 35A ). Abdominal segment VII elongate, nearly as long as three preceding abdominal segments together ( Figs 5P , 35D ). Posterior margin of abdominal mediotergite VII with a short median process ( Fig. 35E ). Posterior margin of abdominal segment VII with three processes, dorsally above terminating each connexivum with a relatively slender process directing ventrad, ventrally with a pointed median process ( Fig. 35E–G ).

Dealated macropterous female

Similar to apterous female in general structure and coloration with following exceptions: thorax with a pronotal lobe, anterior part with a subrhombic yellow marking, posterior part elongate, covering most of mesonotum; posterior margin broadly rounded and brownish ( Fig. 3Q ).

MEASUREMENTS. Body length 10.01, width 2.86, head width 1.51, interocular width 0.60, eye length (dorsal view) 0.58; relative lengths of antennal segments I–IV: 3.98: 1.08:1.22:0.98; pronotum: length 3.12, width 2.41; mesonotum width 2.86; metanotum: length 0.73, width 2.62; abdomen length (ventral view) 4.80; abdominal sternum VII: length 1.46, width 1.79; abdominal mediotergite I: length 0.39, width 1.15; relative lengths of leg segments (femur:tibia: tarsal segment I:tarsal segment II): fore leg: 4.68:3.85:1.91: 0.97, middle leg: 12.47: 6.77: 3.32:0.33, hind leg: 13.31:5.13: 0.17: 0.23.

Apterous male

MEASUREMENTS. Body length 6.20–7.32, width 1.80–2.09, head width 1.43, interocular width 0.59, eye length (dorsal view) 0.60; relative lengths of antennal segments I–IV: 3.58: 1.04:1.07:0.84; pronotum: length0.76, width 1.55; mesonotum:length 2.16, width 2.09;metanotum:length0.69, width 1.88; abdomen length (ventral view) 2.69; abdominal sternum VII: length 0.53, width 1.22; abdominal mediotergite I: length 0.34, width 0.70; relative lengths of leg segments (femur:tibia: tarsal segment I:tarsal segment II): fore leg: 3.49: 2.91:1.06:0.62, middle leg: 10.02: 5.11: 2.17: 0.35, hind leg: 10.04: 2.79:0.11:0.13.

C OLORATION. Median black spot of head posteriorly bifurcate. Pronotum mainly black with a median brownish-yellow spot. Mesonotum mainly black with a median brownish-yellow stripe. Metanotum chiefly blackish, without yellow markings ( Fig. 35I ). Connexivum dorsally blackish. Mesosternum chiefly blackish with a median subtriangular yellowish spot, narrower than that of female ( Fig. 35K ). Abdominal venter light yellow.

LEG. Middle trochanter with one spine; middle femur with scattered small spines, not arranged in distinct row ( Fig. 35L ).

GENITALIA. Abdominal segment VIII ventro-laterally impressed. Pygophore large, ovate. Proctiger with rounded lobes laterally ( Figs 7G , 35I ). Paramere relatively slender, strongly curved at basal fourth, distal part tapering towards hook-shaped apex ( Figs 8M , 35J ).

Dealated macropterous male

Similar to apterous female in general structure and coloration with following exceptions: thorax with a pronotal lobe, anterior part with a subrhombic yellow marking, posterior part elongate, covering most of mesonotum; posterior margin broadly rounded and brownish ( Figs 5P , 35J ).

MEASUREMENTS. Body length 6.39, width 1.85, head width 1.22, interocular width 0.47, eye length (dorsal view) 0.49; relative lengths of antennal segments I–IV: 3.24:0.93: 0.90: 0.79; pronotum: length 2.40, width 1.81; mesonotum width 1.85; metanotum: length 0.49, width 1.68; abdomen length (ventral view) 2.29; abdominal sternum VII: length 0.53, width 0.97; abdominal mediotergite I: length 0.25, width 0.69; relative lengths of leg segments (femur:tibia: tarsal segment I:tarsal segment II): fore leg: 3.66:3.11:1.34: 0.60, middle leg: 10.48: 5.32:2.26:0.33, hind leg: 11.02: 3.56: 0.13: 0.18.

Distribution

China: Guangxi (first record); Taiwan ( Andersen & Chen 1995).

Comparative notes

The female of R. takahashii can be distinguished from all other species of Rhyacobates by the combination of following characters: in the females, the posterior margin of abdominal segment VII has three processes, including an erect, elongate and angular process terminating each connexivum, which is directed ventrad, and a pointed, slender median process ventrally ( Fig. 35F–G ).

Figures

Fig. 2. Habitus of Rhyacobates spp. in dorsal view (females), apterous form if not stated otherwise. A. R. abdominalisAndersen & Chen, 1995.B. R. chinensis Hungerford & Matsuda, 1959.C. R. lundbladi (Hungerford, 1957). D. R. scorpio Andersen & Chen, 1995. E. R. svenhedini (Lundblad, 1934). F. R. takahashii Esaki, 1923, dealated macropterous female. Scale bar = 3 mm.

Fig. 3. Photographs of bodies of Rhyacobates spp. in dorsal view (females), apterous form if not stated otherwise.A. R. bui sp. nov. B. R. elongatus sp. nov. C. R. turgidus sp. nov., apterous form.D. R. turgidus sp. nov., dealated macropterous form.E. R. abdominalis Andersen & Chen, 1995. F. R. anderseni Tran & Yang, 2006. G. R. angustus Tran & Nguyen, 2016, holotype (ZVNU). H. R. chinensis Hungerford & Matsuda, 1959. I. R. constrictus Tran & Nguyen, 2016. J. R. edentatus Andersen & Chen, 1995. K. R. gongvo Tran & Yang, 2006. L. R. lundbladi (Hungerford, 1957). M. R. malaisei Andersen & Chen, 1995. N. R. recurvus Andersen & Chen, 1995. O. R. scorpio Andersen & Chen, 1995. P. R. svenhedini (Lundblad, 1934). Q. R. takahashii Esaki, 1923, dealated macropterous form. R. R. zetteli Tran & Nguyen, 2016. Scale bar = 3 mm.

Fig. 4. Photographs of bodies of Rhyacobates spp. in dorsal view (males), apterous form if not stated otherwise.A. R. bui sp. nov.B. R. elongatus sp. nov.C. R. turgidus sp. nov.D. R. abdominalisAndersen & Chen, 1995. E. R. anderseni Tran & Yang, 2006. F. R. chinensis Hungerford & Matsuda, 1959. G. R. edentatus Andersen & Chen, 1995. H. R. gongvo Tran & Yang, 2006. I. R. lundbladi (Hungerford, 1957). J. R. malaisei Andersen & Chen, 1995. K. R. recurvus Andersen & Chen, 1995. L. R. scorpio Andersen & Chen, 1995. M. R. svenhedini (Lundblad, 1934), apterous form. N. R. svenhedini, macropterous form. O. R. takahashii Esaki, 1923, dealated macropterous form. Scale bar = 3 mm.

Fig. 5. Photographs of bodies of Rhyacobates spp. in lateral view (apterous females). A. R. bui sp. nov. B. R. elongatus sp. nov.C. R. turgidus sp. nov.D. R. abdominalisAndersen & Chen, 1995.E. R. anderseni Tran & Yang, 2006. F. R. angustus Tran & Nguyen, 2016, holotype (ZVNU). G. R. chinensis Hungerford & Matsuda, 1959. H. R. constrictus Tran & Nguyen, 2016. I. R. edentatus Andersen & Chen, 1995. J. R. gongvo Tran & Yang, 2006. K. R. lundbladi (Hungerford, 1957). L. R. malaisei Andersen & Chen, 1995. M. R. recurvus Andersen & Chen, 1995. N. R. scorpio Andersen & Chen, 1995. O. R. svenhedini (Lundblad, 1934). P. R. takahashii Esaki, 1923. Q. R. zetteli Tran & Nguyen, 2016. Scale bar = 3 mm.

Fig. 7. Proctiger of Rhyacobates spp. in dorsal view (males). A. R. gongvo Tran & Yang, 2006. B. R. undbladi (Hungerford, 1957). C. R. malaisei Andersen & Chen, 1995. D. R. recurvus Andersen & Chen, 1995. E. R. scorpio Andersen & Chen, 1995. F. R. svenhedini (Lundblad, 1934). G. R. takahashii Esaki, 1923. H. R. zetteli Tran & Nguyen, 2016. Scale bar = 0.2 mm.

Fig. 8. Paramere of Rhyacobates spp. in lateral view. A. R. bui sp. nov. B. R. elongatus sp. nov. C. R. turgidus sp. nov. D. R. abdominalis Andersen & Chen, 1995. E. R. anderseni Tran & Yang, 2006. F. R. chinensis Hungerford & Matsuda, 1959. G. R. edentatus Andersen & Chen, 1995. H. R. lundbladi (Hungerford, 1957). I. R. malaisei Andersen & Chen, 1995. J. R. recurvus Andersen & Chen, 1995. K. R. scorpio Andersen & Chen, 1995. L. R. svenhedini (Lundblad, 1934). M. R. takahashii Esaki, 1923. Scale bar = 0.2 mm.

Fig. 35. Morphological features of Rhyacobates takahashii Esaki, 1923. A. Body of female, dorsal view. B–C. Body of female, excluding head and prothorax, ventral view. D. Body of female, lateral view. E. Abdominal end of female, dorsal view. F. Abdominal end of female, ventral view. Abdominal end of female, lateral view. H. Body of male, dealated macropterous form, lateral view. I–J. Body of male, apterous form (I) and dealated macropterous form (J), dorsal view. K. Body of male, excluding head and prothorax, ventral view. L. Basal part of right middle leg of male, ventral view. M. Proctiger of male, dorsal view. N. Left paramere, lateral aspect, two different views. Scale bars: A–L = 1 mm; M–N = 0.2 mm.