Metrocoris triangulatus Zettel & Chen, 1996

A. D., Tran & Polhemus, D. A., 2017, The genus Metrocoris Mayr, 1865 (Gerromorpha: Gerridae) in Vietnam, with descriptions of five new species, Raffles Bulletin of Zoology 65, pp. 109-149 : 130-131

Metrocoris triangulatus Zettel & Chen, 1996

( Figs. 22, 23 , 40 , 86–89 )

Metrocoris triangulatus Zettel & Chen, 1996: 152 , 177–178, Figs. 48–52 (type locality: Vietnam, An Khe – Buon Luoi ).

Material examined. Holotype (apterous male), VIETNAM, Gia Lai Prov.: “ 40km NW An Khe, Buon Luoi , 14°10′N, 108°30′E, 620–750 m, 28.3. – 12.4.1995, leg. Pacholátko & Dembicky” ( NHMW) . Paratype: VIETNAM: 1 female (apt), same locality label as holotype ( NHMW) .

Others : VIETNAM: Thanh Hoa Prov.: 1 male, 1 female (apt), 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) ; 1 female (mpt), Pu Hu Nature Reserve , Quan Hoa, Hien Chung, Ban Pheo, Ham stream, coll. Pham T.D., 09 April 2013, PH 1303 ( ZMHU) . Da Nang Prov. : 12 males, 7 females (apt), 1 male, 3 females (mpt), Ba Na - Nui Chua, Suoi Cat Lon, 700 m asl, coll. Tran A.D. & Tan H.H., 28 February 2005, THH05-19 ( NHMW, ZMHU, ZRC) . Kon Tum Prov.: 11 males, 47 females (apt), small stream 60 km NE. of Kontum on Hwy. 24, 1035 m asl, 14°35′43″N, 108°17′49″E, water temp. 18°C, 6 March 2001, CL 4280, coll. J.T. Polhemus & P. Nguyen ( USNM, BPBM) . Gia Lai Prov.: 2 males, 6 females (apt), 1 male (mpt), 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) ; 4 males, 17 females (apt), 2 females (mpt), small hill stream in primary forest, 68 km N. of An Khe , 840 m asl, 14°20′52″N, 108°32′57″E, water temp. 21°C, 22 March 2001, CL 4311, coll. D.A. Polhemus, J.T. Polhemus & P. Nguyen ( USNM, BPBM) ; 1 male, 1 wingless female (apt), small stream 2 km N. of Tram Lap along forest road, 19 June 1996, ROM-961066, 14°26′N, 108°33′E, primary rainforest, 900 m asl, coll. B. Hulbey ( USNM) .

Diagnosis. Body dorso-ventrally compressed. Male: fore femur slender, not modified ( Fig. 86 ); pro-, meso-, metapleuron, meso-, metanotum and abdominal tergum 1 with black setae. Male genitalia small: pygophore short, sub-ovate on ventral view and directed dorsad on lateral view; paramere curved, proximal part broader than distal part, apex narrowly rounded ( Figs. 40 , 87 ); endosoma as in Figs. 88, 89 . Female: thoracic segments without black setae; sternum 7 large, about as long as previous sterna together, posterior margin broad, slightly arched ( Fig. 90 ).

Size: apterous males: length 5.40–6.30 (holotype 6.30), width 3.38–3.50 (holotype 3.50), macropterous males: length 5.20 (wings broken), width 3.04; apterous females: length 4.80–5.00, width 3.20–3.33, macropterous females: length 6.60–6.90, width 3.04–3.10.

Additional description of macropterous morph. Colour: Dorsal head yellow with two small brown spots on the interocular area (similar to apterous form). Pronotum mainly yellow with brown markings: anterior margin black, a pair of brown sub-lateral stripes slender, confluent with a brown median stripe anteriorly and posteriorly, posterior margin from humeri to apex light yellow. Wings brownish, anterior margin with dense black hairs. Colour of antenna and legs similar to apterous form.

Macropterous male: Head width 1.51, interocular width 0.51, eye size 0.75. Lengths of antennal segments: 2.57: 1.17: 0.89: 0.70. Pronotum length 3.00, width 2.35, apex of pronotal lobe round. Lengths of leg segments (femur: tibia: tarsus 1 + 2): fore leg: 2.35: 2.30: 0.75; middle leg: 6.50: 5.30: 1.98; hind leg: 6.70: 3.82: 0.57. Other structural characteristics as in apterous male.

Macropterous female: Head width 1.49, interocular width 0.57, eye size 0.73. Lengths of antennal segments: 1.76: 0.87: 0.82: 0.67. Pronotum length 2.81, width 2.28, apex of pronotal lobe round. Lengths of leg segments: fore leg: 1.80: 1.94: 0.70; middle leg: 5.60: 4.41: 1.84; hind leg: 5.60: 3.33: 0.56. Other structural characteristics as in apterous female.

Remarks. Zettel & Chen (1996) discussed the similarity of M. triangulatus with other species that possess pleural black setae, i.e., species of the M. ciliatus group (sensu Chen & Nieser, 1993) and the M. philippiensis group (sensu Chen & Nieser, 1993, including M. sunda D. Polhemus and M. tigrinus D. Polhemus). However, the form of the male parameres (short and only slightly curved) and the structure of endosoma sclerites of M. sunda and M. tigrinus clearly separate them from the M. ciliatus group. Zettel & Chen (1996) also noted that M. triangulatus was also relatively similar to M. tenuicornis because both species have similar leg structures (fore femur slender, middle and hind legs very long), and small genital segments. However, M. triangulatus can be separated from the latter by the black setae on the pleura (in males), the shape of male paramere and the shape of sternum 7 in the female.

Metrocoris triangulatus matches all diagnostic characteristics of the M. ciliatus group (see Remarks for M. inthanon ), particularly the presence of black pleural setae in males and the shape of female sternum 7, thus it can be placed in this species group. Metrocoris triangulatus differs from other species in the M. ciliatus group by the shape of body, the very small genital segments, and the shape of the male paramere. For further comparisons, see Remarks under M. sicilis , new species.

Distribution. Vietnam: Thanh Hoa (first record), Kon Tum (first record), Da Nang (first record), Gia Lai ( Fig. 140 ).

Figures

Figs. 18–31. Dorsal colour patterns of Metrocoris species. 18, 19: M. inthanon, specimens from Vietnam, Nghe An Prov., Pu Mat Nature Reserve (CL 4385). 20, 21: M. sicilis, new species, paratypes, from Vietnam, Hanoi, Ba Vi N’Park (CL 4393). 22, 23: M. triangulatus, specimens from Vietnam, Kontum Prov., 60 km NW. of Kontum (CL 4280). 24, 25: M. nigriventris, new species, paratypes, from Vietnam, Lai Chau Prov., 12 km N. of Lai Chau (CL 4410). 26, 27: M. monticola, new species, paratypes, from Vietnam, Lao Cai Prov., Sa Pa, Sin Chai (TAD1363). 28, 29: M. sapa, new species, paratypes, from Vietnam, Lao Cai Prov., Sa Pa, Nui Xe (TAD0416). 30, 31: M. tenuicornis, specimens from Vietnam, Gia Lai Prov., 60 km N. of An Khe (CL 4309).

Figs. 32–43. Parameres of Metrocoris species. 32: M. stranguloides, specimen from Vietnam, Gia Lai Prov., 60 km N. of An Khe (CL 4309). 33: M. bilobatoides, specimen from Vietnam, Lao Cai Prov., 12 km NW. of Sa Pa (CL 4404). 34: M. johnpolhemi, new species, specimen from Vietnam, Lai Chau Prov., Nam Ceung stream (CL 4409). 35: M. quynhi, specimen from Vietnam, Lao Cai Prov., 18 km NW. of Sa Pa (CL 4400). 36: M. obscurus, specimen from Vietnam, Lao Cai Prov., 4 km NE. of Sa Pa (CL 4407). 37: M. acutus, specimen from Vietnam, Hai Hung Prov., 22 km N. of Chi Linh (CL 4375). 38: M. nigrofascioides, specimen from Vietnam, Binh Dinh Prov., An Khe Pass (CL 4291). 39: M. sicilis, new species, specimen from Vietnam, Hanoi, Ba Vi N’Park (CL 4393). 40: M. triangulatus, specimen from Vietnam, Gia Lai Prov., N. of Tram Lap (ROM-961066). 41: M. ciliatus, paratype, from Vietnam, Lai Chau Prov., Muong Te (TAD1329). 42: M. nigriventris, new species, paratype, from Vietnam, Lao Cai Prov., 20 km NE. of Sa Pa (CL 4406). 43: M. monticola, new species, paratype, from Vietnam, Lao Cai Prov., Sa Pa, Sin Chai (TAD1363).

Figs. 80–90. Morphological features of Metrocoris species. 80–83: M. ciliatus, macropterous male. 80: right fore leg. 81, 82: left paramere, two different views. 83: endosomal sclerites, lateral view. 84, 85: M. inthanon. 84: right fore leg of male. 85: apex of abdomen, female, ventral view. 86–90: M. triangulatus. 86–89: male holotype. 86: A, right fore leg. 87: left paramere. 88, 89: endosomal sclerites, lateral and dorsal views. 90: abdomen of female, ventral view (80, 84, 86 same scale; 81–83 same scale; 85, 90 same scale).

Figs. 44–55. Morphological features of Metrocoris species. 44–46: M. stranguloides. 44, 45: right fore legs of male. 46: sternum 7 of female, ventral view. 47–51: M. bilobatoides. 47, 48: right fore leg of male, same scale. 49, 50: tergum 7 of female, dorsal view (49: specimen from Tam Dao; 50: specimen from Lao Cai). 51: sternum 7 of female, ventral view. 52–55: M. vietnamensis (52–55 reproduced and modified from Tran & Zettel, 2005). 52, 53: right fore legs of male. 54: left paramere. 55: sternum 7 of female, in situ (44, 45, 47, 48, 52, 53 same scale; 46, 49–51, 55 same scale).

Fig. 140. Distribution records in Vietnam of Metrocoris ciliatus, M. inthanon, Metrocoris sicilis, new species, and M. triangulatus.