Metrocoris tenuicornis Esaki 1926
Creators: name: A. D., Tran
name: Polhemus, D. A.
Publisher: name: Zenodo
Year: 2017
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Hemiptera
Gerridae
Metrocoris
Metrocoris tenuicornis

description: Metrocoris tenuicornis Esaki, 1926
(Figs. 30, 31, 123–136)
Metrocoris tenuicornis Esaki, 1926: 125, Figs. 3 c–e (type locality: Annam, Vietnam); den Boer, 1965: 28–29, Figs. 36, 48, 63–64 (additional notes); Cheng, 1966: 273–282, Figs. 1–25 (life history); Polhemus, 1990: 18–19, Figs. 14, 34–35, 49 (redescription); Chen & Nieser, 1993: 70–72, Figs. 183–184, 196, 202 (redescription); Zettel & Chen, 1996: 152, 178 (faunistic notes).
Material examined. Syntypes: 1 macropterous male, 1 apterous female, “ Annam, Laos ” / “det. T. Esaki ” (MTMB) (hereby, the macropterous male is designated as lectotype and the apterous female is desginated as paralectotype).
Others: VIETNAM: Dien Bien Prov.: 1 male (mpt), Na Tau, Nam Rom river, coll. Tran A.D., 25 July 2004, DY0412 (ZRC). Hai Duong Prov.: 3 males, 3 females (apt), Kheao stream, 23 km N. of Chi Linh, 125 m asl, water temp. 17°C, 25 March 2000, CL 4376, coll. J.T. Polhemus & P. Nguyen (USNM). Thanh Hoa Prov.: 1 female (apt), Ben En N’Park, Ngòn stream, near Bang ranger station, coll. Pham T.D., 03 August 2012, BE1205 (ZMHU); 3 females (apt), Ben En N’Park, Nhu Xuan, Khe May stream, coll. Pham T.D., December 2012, BE1206 (ZMHU); 1 female (apt), Ben En N’Park, Nhu Xuan, Tan Binh, Xuan Ly ranger station, Khe Lo 4 stream, coll. Pham T.D., 26 February 2013, BE1301 (ZMHU); 2 males, 1 female (apt), Ben En N’Park, Nhu Xuan, Son Binh, Khe Cay Khe stream, at junction with road, coll. Pham T.D., 01 March 2013, BE1307 (ZMHU); 2 females (apt), Ben En N’Park, Nhu Xuan, Duc Luong, Khe Cau Da stream, coll. Pham T.D., 08 March 2013, BE1309 (ZMHU); 3 males, 13 females (apt), 1 female (mpt), Ben En N’Park, Nhu Xuan, Xuan Quy, Song Chang ranger station, Khe Khoanh 2 stream, coll. Pham T.D., 11 March 2013, BE1310 (ZMHU). Quang Binh Prov.: 4 males, 2 females (apt), Phong Nha, a stream 1 km behind Forest Ranger station 4, coll. Tran A.D., 16 July 2004, DY0409 (ZRC). Kon Tum Prov.: 7 males, 8 females (apt), shallow trib. to stream 2 km inside Chu Mom Ray Nature Reserve, 635 m asl, 14°25′55″N, 107°42′50″E, water temp. 21.5°C, 4 March 2001, CL 4278, J.T. Polhemus and P. Nguyen (USNM, BPBM); 1 male, 1 female (apt), stream 63 km NE. of Kontum on Hwy. 24, 1050 m asl, 14°36′14″N, 108°18′22″E, water temp. 20.5°C, 6 March 2001, CL 4281, coll. J.T. Polhemus & P. Nguyen (USNM). Gia Lai Prov.: 1 male (apt), 40 km, NW. An Khe, Buon Luoi, 14°10′N, 108°30′E, 620–750 m asl, 28 March–12 April 1995, coll. Pacholátko & Dembicky (NHMW); 11 males, 18 females (apt), Tral Stream, 60 km N. of An Khe, 700 m asl, 14°20′28″N, 108°34′49″E, water temp. 23.5°C, 22 March 2001, CL 4309, coll. D.A. Polhemus, J.T. Polhemus & P. Nguyen (USNM, BPBM). Lam Dong Prov.: 7 males, 8 females (apt), lake at Valley of Love, 5 km N. of Dalat, 1495 m asl, 11°58′39″N, 108°27′00″E, 11 May 1998, CL 3086, coll. J.T. Polhemus (USNM); 10 males, 6 females (apt), stream in pine forest 13 km N. of Dalat on Suoi Vang road, 1495 m asl, 11°59′26″N, 108°23′19″E, water temp. 21.5°C, 28 March 2001, CL 4317, coll. D.A. Polhemus, J.T. Polhemus & P. Nguyen (USNM, BPBM). Dong Nai Prov.: 1 male, 3 females (apt), Nam Cat Tien, Lan stream B, coll. Tan H.H. et al., 10 May 2001, THH0128 (ZRC); 1 male (apt), Vinh Cuu, Vinh An, Suoi Rang, coll. Tran A.D., 10 May 2003, TAD0315a (ZRC); 1 female (apt), Vinh Cuu, Ma Da, Suoi Sai (Sai stream), up-stream from bridge, coll. Tran A.D., 31 October 2009, TAD0918 (ZMHU); 1 male (mpt), Cat Tien N’Park, feeder stream of Bau Chim (Bird lake), coll. Tran A.D., 7 November 2009, TAD0930 (ZMHU); 7 males, 3 females (apt), Cat Tien N’Park, Cay Si stream, coll. Tran A.D. & Pham T.D., 09 April 2010, PTD1002 (ZMHU). Kien Giang Prov., Phu Quoc island: 5 males, 6 females (mpt), Tranh stream (at lower section), coll. Tran A.D. et al., 30 November 2010, TAD1021 (ZMHU); 4 males (mpt), Tranh stream (middle section & waterfall), coll. Tran A.D., 30 November 2010, TAD1022 (ZMHU).
LAOS: Vientiane Prov.: 7 males, 6 females (apt), 1 male (mpt), Ban Van Heue, ~ 20 km E. of Phou Khao Khouay park HQ, 1039 m asl, vic. 18°17′44″N, 102°53′48″E, 31 August 1967, coll. J.L. Gressit et al. (BPBM).
CAMBODIA: Koh Kong Prov.: 2 males, 3 females (apt), Cardamom Mountains, stream approx. 31 km NE. of Koh Kong on road to Pursat, 310 m asl, 11°41′03″N, 103°06′56″E, water temp. 26°C, 30 August 2015, CL 6021, coll. D.A. Polhemus (BPBM, USNM).
THAILAND: Chiang Mai Prov.: 1 male (apt), N. Thailand, 55 km to Chiang Mai, coll. Y.Y. Goh, 13 June 1998, GYY86 (ZRC).
MALAYSIA: Perak: 1 male, 1 female (apt), ZRC.6.19655, stream about 195 km to Ipoh (40 km to Gerik) from Baling, coll. H.K. Lua, 20 February 1997, LHK0331 (ZRC); 1 male, 1 female (apt), ZRC.6.19656, Carut Bt. Sebelah, rocky stream, about 2 km before Baling on Gerik, Sg. Pentani Rd, coll. H.K. Lua, 18 February 1997, LHK0327 (ZRC). Sabah: 3 males (apt), Maliau Basin, Sungei Maliau, upstream, coll. K.L. Yeo, 15 May 1996, MB13 (ZRC); 1 male, 3 females (apt), Maliau Basin, Sungei Maliau, upstream, coll. K.L. Yeo, 15 May 1996, MB15 (ZRC); 1 female (apt), Maliau Basin, Heath forest stream, coll. T.B. Lim & K.L. Yeo, 22 May 1996, MB25 (ZRC); 2 males, 1 female (apt), Maliau Basin, Sungei Maliau, upstream, coll. T.B. Lim, 21 May 1996, MB24 (ZRC); 2 females (apt), Maliau Basin, Sungei Maliau, upstream, near Camp 96, coll. T.B. Lim & K.L. Yeo, 14 May 1996, MB4 (ZRC); 1 male, 2 females (apt), Maliau Basin, tributary of Sungei Maliau, upstream, coll. T.B. Lim & K.L. Yeo, 23 May 1996, MB26A (ZRC); 1 male, 3 females (apt), Maliau Basin, Sungei Maliau, near to base camp, coll. G. Gunsalam, 15 May 1996, MB28 (ZRC); 1 male, 2 females (apt), Maliau Basin, Sungei Maliau, upstream, near Camp 96, coll. T.B. Lim & K.L. Yeo, 14 May 1996, MB2 (ZRC); 2 males, 3 females (apt), Maliau Basin, Sungei Maliau, near to base camp (Heliped), coll. G. Gunsalam, 17 May 1996, MB36 (ZRC); 3 males, 3 females (apt), Maliau Basin, coll. G. Gunsalam, 14 May 1996, MB4A (ZRC); 1 female (apt), Maliau Basin, coll. G. Gunsalam, 14 May 1996, MB1A (ZRC); 1 female (apt), Maliau Basin, Sungei Maliau, upstream near Camp 96, coll. T.B. Lim, 13 May 1996, MB1 (ZRC); 1 female (apt), 1 female (mpt), Maliau Basin, near Heliped, coll. G. Gunsalam, 15 May 1996, MB30 (ZRC); 1 female (mpt), Maliau Basin, Sungei Maliau tributary, Camp 88II, coll. K.L. Yeo, 16 May 1996, MB17 (ZRC); 1 female (apt), Maliau Basin, Sungei Maliau, upstream, near Camp 96, coll. T.B. Lim & K.L. Yeo, 14 May 1996, MB2 (ZRC). Sarawak: 1 male, 1 female (apt), Sarawak, Semengoh NSG, 30 km S. Kuching, coll. H. Zettel (2), 17 February 1993 (NHMW).
SINGAPORE: 1 female (apt), MacRitchie, Sime Rd, coll. H.K. Lua et al., 2 June 1994, NS148I (ZRC); 9 males, 14 females (apt), MacRitchie, Sime Rd, coll. H.K. Lua et al., 2 June 1994, NS148H (ZRC); 6 males, 17 females (apt), MacRitchie, Sime Rd, coll. H.K. Lua et al., 2 June 1994, NS148E (ZRC); 9 males, 19 females (apt), MacRitchie, Sime Rd, coll. H.K. Lua et al., 2 June 1994, NS148G (ZRC); 2 males, 4 females (apt), 1 male (mpt), ZRC.6.5079–5087, Bukit Timah, coll. C.F. Lim, [date unknown] (ZRC); 1 male (apt), 1 male, 1 female (mpt), Rifle Range Rd, stream, coll. D.H. Murphy, March 1986 (ZRC); 2 males, 12 females (apt), Rifle Range Rd, coll. D.H. Murphy, March 1986 (ZRC); 8 males, 7 females (apt), Nee Soon, swamp forest stream, coll. D.H. Murphy, 3 January 1986 (ZRC); 5 males, 8 females (apt), Rifle Range Rd, secondary stream, coll. Y.H. Lim et al., 3 June 1993, NS109 (ZRC); 13 males, 4 females (apt), stream leading to MacRitchie Reservoir from Thomson ridge, plot 3, coll. Del Sim, 29 April 1993, NS64 (ZRC); 9 males, 26 females (apt), Nee Soon swamp forest, Plot 25, coll. H.K. Lua et al., 21 April 1993, NS51 (ZRC); 8 males, 18 females (apt), SICC, Upper Peirce stream near Plot 8 & 9, coll. C.Y. Chang, 25 May 1993, NS95 (ZRC); 4 females (apt), 1 male (mpt), Rifle Range Rd, coll. H.K. Lua et al., 28 April 1993, NS61 (ZRC); 1 male, 6 females (apt), Chestnut Drive forest swamp, Plot 56-57, coll. H.K. Lua, 22 April 1993, NS55 (ZRC); 1 male, 3 females (apt), Sime Rd, small stream near Plot 6, coll. C.M. Yang et al., 7 April 1993, NS29 (ZRC); 1 male (apt), Upper Peirce Reservoir, Plot No. 31, coll. K.L. Yeo et al., 26 May 1993, NS60 (ZRC); 1 male, 1 female (apt), SICC, Upper Peirce stream, coll. C.Y. Chang, 24 May 1993, NS93 (ZRC); 11 females (apt), Sime Road forest, NW. of SICC Golf Course, Plot 22, coll. K.K.P. Lim et al., 26 April 1993, NS57 (ZRC); 6 males, 15 females (apt), Upper Peirce Reservoir stream, Plot 23, coll. Y.H. Lim et al., 17 May 1993, NS84 (ZRC); 1 male (apt), Nee Soon swamp forest, Central Catchmen survey, coll. K.K.P. Lim et al., 15 April 1993 (ZRC); 6 females (apt), MacRichie Reservoir, near Plot 17, pond, coll. C.M. Yang et al., 13 April 1993, NS34 (ZRC); 1 female (apt), MacRitchie Reservoir, SICC near Plot 4, [collector unknown], 28 May 1993, NS104 (ZRC); 4 males, 14 females (apt), Seletar Reservoir inlet, along Mandai Rd, coll. H.K. Lua et al., 14 April 1993, NS41 (ZRC); 4 males, 4 females (apt), Bukit Timah Nature Reserve, coll. C.M. Yang et al., 1 October 1991, YCM30 (ZRC).
INDONESIA: 2 males (apt), Riau, Pulau Bintan, [collector unknown], 20 November 1996 (ZRC); 1 male, 1 female (apt), East Java, 60 km SW. Banyuwangi, Meru Betiri N’Park, W. Sumber Sari, 80 m asl, coll. Schillhammer (12), 4 October 1995 (NHMW).
PHILIPPINES: 1 male, 1 female (apt), Palawan, 9 km W. P. Princesa Iwahig, Balsahan river, coll. Zettel (48), 24 March 1994 (NHMW); 2 males, 1 female (apt), Palawan, W. Sabang, 0–30 m, coll. H. Zettel (52e), 29 March 1994 (NHMW); 2 males, 1 female (apt), Mindoro, Mindoro Beach, 10 km W. Puerto Galera, coll. H. Zettel (31a), 23 November 1993 (NHMW).
Diagnosis. Basic dorsal pattern as in Figs. 30, 31, the darkness of brown markings variable (from dark brown to yellowish brown). Sexual dimorphism distinct, males are larger and with longer legs than females. Male: fore femur (Fig. 123) slender (ratio of length/width around 8.2) constricted sub-apically, with small, blunt sub-apical elevation on ventral (variable in some populations: indentation not distinct); middle and hind legs usually very long (lengths variable). Male genitalia moderate size; paramere short, distally curved, constricted then widened before apex, tip of paramere pointed, slightly curved outwards (on posterior view, in-situ) (Figs. 124–128, 131–136); endosoma structure as in Fig. 129. Female: sternum 7 large, slightly shorter than all preceding abdominal sterna combined, usually directed dorsad, posterior margin almost straight (Fig. 130).
Size: apterous males: length 4.60–6.70, width 2.44–3.30, macropterous males: length 5.70–7.10, width 2.38–3.17; apterous females: length 3.75–5.40, width 2.18–2.90, macropterous females: length 6.80, width 2.81–2.85.
Additional description of lectotype. Macropterous male: Size: length 6.40, width 3.20. Head width 1.70, interocular width 0.60, eye size 0.85. Antennae broken. Pronotum/length 3.23, width 2.54. Lengths of leg segments (incomplete, some segments broken off): fore leg: 2.71: 2.64: 0.11: 0.90; middle femur: 10.6; hind leg: 10.5: 6.50: 0.48: 0.27. Fore femur slender, ratio of length/width = 8.2 (width 0.33), ventral surface with a small indentation near apex.
Remarks. Esaki (1926) described M. tenuicornis without providing detailed descriptions of the male genitalia (parameres, endosoma). The type locality is “ Annam, Laos ”. The particular location is doubtful, but probably somewhere in the central part of Vietnam (despite the word “ Laos ” in the label, Annam was a popular name referring to the central part of Vietnam in the early 19 th Century, which shared a border with Laos, see Sterling et al., 2006). Den Boer (1965) gave additional notes on the endosomal structure, but he did not describe the parameres of the insect. He also examined the syntypes at the Hungarian Museum, Budapest but did not designate a lectotype. Polhemus (1990) gave a detailed description of this species, based on series of specimens from Peninsular Malaysia, Borneo, Sumatra, the Philippines, Myanmar, India, and Hong Kong, but did not have any material available from Vietnam. Chen & Nieser (1993), when revising the genus Metrocoris, gave some descriptive notes and illustrations of this species. However, the types were not physically examined during either of these two studies. The illustrations of the male paramere in the works of Polhemus (1990: Fig. 34) and of Chen & Nieser (1993: Fig. 196), do not match the paramere of the type specimen. During the course of this study, the syntypes were examined by the first author, and the macropterous male is hereby designated as lectotype to fix the taxonomy of this species (paralectotype: apterous female, in poor condition).
Chen & Nieser (1993) placed M. tenuicornis in its own monotypic species group, the M. tenuicornis group, but provided no diagnosis or defining character states for this group (although their comparative notes regarding M. tenuicornis could presumably be taken as the diagnosis for this species group). Recently, Basu et al. (2016) described M. lavitra from West Bengal, India, but indicated that it did not fall into any currently defined species group within the genus. We consider M. lavitra to be a member of the M. tenuicornis group, based on the following characters: (1) fore femur of the male slender, bearing at most a single very small tooth distally near the ventral apex, or unarmed altogether; (2) male paramere crescent-shaped and apically expanded to form an oblique head of variable size (Figs. 131–136); (3) male endosoma with dorsal sclerite long and recurved proximally, ventral sclerite with a tightly coiled extension projecting beyond margin of endsomal capsule (Fig. 129); (4) middle and hind legs of the male usually extremely long, with the length of the middle femur exceeding 10 mm in some specimens, and the length of the hind femur exceeding 8 mm (this character is subject to a degree of intrasexual variability, such that not all individuals exhibit the extreme femoral prolongation, as also noted by Chen & Nieser, 1993).
By examining “ Metrocoris tenuicornis ” populations from different areas in Southeast Asia, we observed that there are variations in the structure of the male fore femur (subapical indentation sometimes not distinct) and parameres (the constriction before apex is variable, see Figs. 124, 125, 127, 128, 131–136), but that the male endosomal structures are uniform throughout. Overall, the male paramere shapes in “ Metrocoris tenuicornis ” and M. lavitra seem to form a morphocline (Figs. 131–136), although this progression of shapes does align with any clear east-west geographic trend across Indochina and into India. The male paramere shape in M. lavitra is most similar to that seen in the specimen of M. tenuicornis that we have illustrated from Burma (Fig. 131), and represents a more extremely modified example at one end of this character state series. It is possible that the M. tenuicornis group as we have defined it herein contains a set of cryptic sibling species, but such a conclusion is premature, and would be most effectively investigated using molecular techniques. As such, all Vietnamese populations that currently key to M. tenuicornis are treated as conspecific in the context of the present work, until further evidence can be found to justify taxonomically subdividing this assemblage.
Distribution. Vietnam: Dien Bien, Hai Duong, Thanh Hoa, Quang Binh, Kon Tum, Gia Lai, Lam Dong, Dong Nai, Phu Quoc (Fig. 141). Extralimital records: China, Hong Kong, Southeast Asia from mainland, including Cambodia (first record), Laos (confirmed record), to the Malay Archipelago and the Philippines (see Chen & Nieser, 1993).
Habitats. Metrocoris tenuicornis is often found skating on moderate or slow flowing forest streams. Except for some populations found in mountane areas of Vietnam at the elevations of 620–760 m, this species is mostly found in lowland areas. This habitat preference may contribute to the wide distribution of M. tenuicornis.
description: Published as part of A. D., Tran & Polhemus, D. A., 2017, The genus Metrocoris Mayr, 1865 (Gerromorpha: Gerridae) in Vietnam, with descriptions of five new species, pp. 109-149 in Raffles Bulletin of Zoology 65 on pages 139-143, DOI: 10.5281/zenodo.4502634