Metrocoris Mayr, 1865

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 : 111-112

Metrocoris Mayr, 1865

Metrocoris Mayr, 1865: 445 (type species: Metrocoris brevis Mayr, 1865 , currently Metrocoris stali ( Dohrn, 1860), by monotypy); Esaki, 1926: 122–130; den Boer, 1965: 1–38 (revision); Polhemus, 1990: 1–28 (regional revision: Malay Archipelago & Philippines); Chen & Nieser, 1993: 1–43, 45–82 (revision); Chen, 1994: 124–134 (regional revision: China).

Halobatodes White, 1883: 23 , 58 (type species: Halobatodes histrio White, 1883 , by monotypy); (synonymised by Meinert, 1888: 140).

Gerastratus Distant, 1910: 148 (type species: Gerastratus foveatus Distant, 1910 , by monotypy); (synonymised by Esaki, 1929: 417–418).

Euodos Distant, 1910: 150 (type species: Euodos communis Distant, 1910, by monotypy); (synonymised by Esaki, 1929: 418–419).

Metrocoropsis Paiva, 1919: 365 (type species: Metrocoropsis femorata Paiva, 1919 , by monotypy); (synonymised by Esaki, 1926: 122).

Remarks. The genus Metrocoris Mayr is recognised by the following characteristics (after Chen & Nieser, 1993): They are medium sized gerrids (length of males 4.3–8.3, females 3.8–8.3), with body usually not dorso-ventrally depressed, having both apterous and macropterous forms. Dorsum of body is usually yellowish with distinct dark markings; venter of body is usually pale (with the exception of some species in the M. compar species group). Eyes are large, but not reaching antero-lateral corners of mesonotum. Fore tarsal segment 1 is much shorter than segment 2. Fore femur of the male is usually incrassate and modified ventrally; fore femur of the female is more slender than that of the male, usually not modified. Male genitalia are usually prominent, with abdominal segment 8 large, pygophore boat-shaped, and parameres well-developed. Endosomal sclerites are variable but characteristic for each species. Sternum 7 of the female is large, usually modified posteriorly, and characteristic for different species groups.

Chen & Nieser (1993: 6) indicated that Kemp (1925) synonymised Metrocoropsis Paiva with Metrocoris Mayr. However , this is not accurate. Kemp (1925: 93–94) only expressed concerns about the resemblances of Metrocoropsis femorata Paiva, 1919 to Metrocoris nigrofasciatus Distant, 1903 , but did not formally synonymise Metrocoropsis Paiva with Metrocoris Mayr. The first person who included Metrocoropsis Paiva into the synonymy list for Metrocoris Mayr was actually Esaki (1926) (see Esaki, 1926: 122).

KEY TO SPECIES OF METROCORIS OCCURING IN VIETNAM

1. Sternum 7 shorter than and not covering genital segments ventrally. Abdominal segment 8 cylindrical, not divided along the midline on the ventral side. ................................ 2 (males)

– Sternum 7 large and broad, usually covering all abdominal segment 8 ventrally. Abdominal semment 8 divided along the midline on the ventral side ( Fig. 90 )................... 17 (females)

Key to males of Metrocoris

2. Fore femur incrassate, ventrally with at least one sub-apical tooth. ........................................................................................3

– Fore femur slender, without sub-apical tooth or only with small sub-apical tooth-like elevation. .............................................10

3. Ventral margin of fore femur sinuate on distal half, appearing bi-concave ( Fig. 71 ); paramere sharply bent on distal one-third, with broadly rounded tumescence subapically on outer margin ( Figs. 36 , 72 ). ........................................................ M. obscurus

– Ventral margin of fore femur with at most a single subapical constriction, not sinuate or biconcave as above; male paramere more evenly curving throughout its length, not sharply bent on distal one-third, without a subapical tumescence on outer margin......................................................................................4

4. Fore femur with a median tooth and two sub-apical teeth ( Figs. 44, 45 )............................................................ M. stranguloides

– Fore femur without a median tooth........................................5

5. Fore femur with a sub-apical indentation, sub-apical edge of indentation marked with a large single tooth ( Figs. 47, 48, 52, 53 , 56, 57 , 77 ).........................................................................6

– Fore femur more or less constricted sub-apically, but without distinct indentation, apically with a bifid or bipartite sub-apical tooth. ........................................................................................9

6. Sub-apical indentation with a distinct small tooth on proximal edge ( Figs. 47, 48, 52, 53 , 77 ). Shaft of paramere not expanded on distal half............................................................................7

– Sub-apical indentation without distinct tooth on proximal edge ( Figs. 56, 57 ). Shaft of paramere expanded on distal half ( Figs. 34 , 61 )........................................ M. johnpolhemi , new species

7. Paramere with apex blunt, expanded to form a small head ( Fig. 38 )............................................................... M. nigrofascioides

– Paramere with apex pointed or narrowly rounded, not expanded to form a small head. ..............................................................8

8. Paramere strongly curved on distal half, apically strongly narrowed ( Fig. 54 ).......................................... M. vietnamensis

– Paramere curved on distal two-thirds, gradually tapering apically ( Fig. 33 ). .......................................................... M. bilobatoides

9. Slightly smaller species (male length 4.6–6.3 mm). Pygophore sub-ovate, with apical margin rounded. Paramere as in Fig. 37 . .............................................................................. M. acutus

– Larger species (male length 6.3–7.0 mm). Pygophore prolonged, with apical margin straight. Paramere as in Figs. 35 , 69 . ....... .................................................................................. M. quynhi

10. Thorax (nota and pleura) with numerous black setae..........11

– Thorax without black setae...................................................15

11. Larger species (length 5.4–6.3 mm), body broad, roughly triangular................................................................................12

– Smaller species (length 4.7–5.4 mm), body sub-ovate........13

12. Fore femur constricted sub-apically, with a small tooth-like elevation ( Fig. 95 ). Paramere long, curved dorsad on distal one-third, proximal part narrower than distal part, apex broadly rounded ( Figs. 39 , 96 ).......................... M. sicilis , new species

– Fore femur simple, without sub-apical elevation. Paramere short, curved dorsad on distal half, proximal part broader than distal part, apex narrowly rounded ( Figs. 40 , 87 ).................... .......................................................................... M. triangulatus

13. Abdominal segment 8 with a median notch on postero-dorsal margin. Paramere larger and gradually thicker distally ( Figs. 91–93 ).................................................................... M. inthanon

– Abdominal segment 8 without median notch on posterior margin. Paramere smaller, sickle-shaped, tapering evenly along its length to a slender apex ( Figs. 41 , 81, 82 ). ...... M. ciliatus

14. Ventral surface of fore femur not notched in the middle, usually with a small sub-apical tooth-like elevation ( Fig. 123 ). Paramere with a sub-apical indentation, apex slightly expanded ( Figs. 124, 125, 127, 128 , 131–136 ). Middle and hind legs often extremely long, length of middle femur usually equal to or exceeding 10 mm ..................................................................... M. tenuicornis

– Ventral surface of fore femur with a notch in the middle; without sub-apical elevation ( Figs. 100 , 108 , 117 ). Paramere without sub-apical indentation. Middle and hind legs usually shorter, length of middle femur less than 8 mm ..................15

15. Male genital segment long bearing dark hairs; colour marks on dorsum dark and distinct, ventral body surface broadly dark (or at least broadly embrowned) throughout its length. ......16

– Male genital segment lacking long dark hairs; dorsal markings less distinct; ventral body surface mostly pale. ....................... ................................................................ M. sapa , new species

16. Paramere curved dorsad on distal half, apex broadened and rounded, curved outwards and posteriorly ( Figs. 110–112 ) .... ....................................................... M. monticola , new species

– Paramere hook-shaped, curved up on distal one-third, apex projecting outward and anteriorly ( Figs. 101–103 ).................. ..................................................... M. nigriventris , new species

Key to females of Metrocoris

(Note: Females can be identified with higher certainty if associated males available)

17. Hind margin of sternum 7 simple, not modified ( Figs. 85, 90 , 99 , 130 )..................................................................................18

– Hind margin of sternum 7 modified (with 1–2 distal lobes or with a notch)..........................................................................22

18. Dorsum and lateral side of thorax covered with black setae. Dark markings on dorsum of body extensive. ..... M. inthanon

– Thorax without black setae. Dark markings on dorsum less extensive. ...............................................................................19

19. Body of triangular appearance, ratio of body length/maximum width ca. 1.5–1.6/1.0.............................................................20

– Body more ovate, ratio of body length/maximum width ca. 1.7–1.9/1.0. ............................................................................21

20. Fore femur sub-apically constricted, ventral surface with subapical elevation..................................... M. sicilis , new species

– Ventral surface of fore femur without sub-apical elevation.... .......................................................................... M. triangulatus

21. Antennal segment 2 shorter than segment 3. ... M. tenuicornis

– Antennal segment 2 longer than segment 3. .......... M. ciliatus

22. Median lobe of sternum 7 bearing 4 lobes on posterior margin, with two large lateral lobes flanking a medially incised bilobate process ( Fig. 70 )....................................................... M. quynhi

– Sternum 7 not as above, with a most 2 lobes flanking a medial incision...................................................................................23

23. Posterior part of sternum 7 modified into a single lobe ( Figs. 46 , 76, 79 , 107 , 116 , 122 ). ...................................................24

– Posterior part of sternum 7 modified into two lobes ( Figs. 51, 55 , 65 , 73 ). ............................................................................29

24. Hind coxa and trochanter elongated.....................................25

– Hind coxa and trochanter not modified as above. ...............27

25. Venter mostly pale. Hind coxa and trochanter covered with long hairs ( Fig. 121 ) .............................. M. sapa , new species

– Venter with dark marks. Hind coxa and trochanter without distinct long hairs..................................................................26

26. Hind trochanter produced apically into a small process ( Fig. 106 ). Apex of abdomen barely surpassing apex of hind coxa. Distal lobe of sternum 7 with almost straight posterior margin ( Fig. 107 )..................................... M. nigriventris , new species

– Hind trochanter not produced apically ( Fig. 115 ). Apex of abdomen clearly surpassing apex of hind coxa, but not surpassing apex of hind trochanter. Distal lobe of sternum 7 with round posterior margin ( Fig. 116 )........... M. monticola , new species

27. Distal lobe of sternum 7 broad, with long dark hairs on lateral margin ( Fig. 46 ). ........................................... M. stranguloides

– Distal lobe of sternum 7 narrow, without long dark hairs. ..... ...............................................................................................28

28. Sternum 7 with a median lobe of sub-rectangular shape directed apically. Pilosity on hind trochanter long and dense ( Fig. 79 )................................................................. M. nigrofascoides

– Sternum 7 with a tongue-like median lobe produced apically with rounded apex. Pilosity on hind trochanter short ( Fig. 76 ).............................................................................. M. acutus

29. Lobes of sternum 7 small and finger-like, separated by a wide, shallow, transverse notch ( Fig. 73 )....................... M. obscurus

– Lobes of sternum 7 large and angular, separated by a deep, longitudinal incision..............................................................30

30. Sternum 7 with notch between the distal lobes narrow and angular ( Fig. 51 ).............................................. M. bilobatoides

– Sternum 7 with notch between the distal lobes wider........31

31. Notch between two distal lobes with rounded margin ( Fig. 55 )................................................................... M. vietnamensis

– Notch between two distal lobes with angular margin ( Fig. 65 ).............................................. M. johnpolhemi , new species

Figures

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. 66–73. Morphological features of Metrocoris species. 66–70: M. quynhi (65–70 reproduced from Tran & Zettel, 2005). 66: right fore leg of male. 67: pygophore, lateral view. 68: male genital capsule, dorsal view. 69: left paramere. 70: female sternum 7, in situ. 71–73: M. obscurus. 71: right fore leg of male. 72: left paramere. 73: sternum 7 of female, ventral view (66, 71 same scale; 67, 68 same scale; 69, 72 same scale; 70, 73 same scale).

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. 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).

Figs. 56–65. Morphological features of Metrocoris johnpolhemi, new species. 56, 57: right fore legs of male. 58: abdominal segment 8 of male, in situ, lateral view. 59: pygophore, lateral view. 60: proctiger of male. 61: left paramere. 62, 63: endosomal sclerites, lateral and dorsal views. 64: tergum 7 of female, dorsal view. 65: sternum 7 of female, ventral view (56, 57 same scale; 58, 59 same scale; 64, 65 same scale).

Figs. 74–79. Morphological features of Metrocoris species. 74–76: M. acutus. 74, 75: right fore legs of male, same scale. 76: sternum 7 of female, ventral view. 77–79: M. nigrofascioides. 77: right fore leg of male. 78: hind trochanter of female. 79: sternum 7 of female, ventral view (74, 75, 77 same scale; 76, 78, 79 same scale).

Figs. 94–99. Morphological features of Metrocoris sicilis, new species. 94: right antenna of male. 95: right fore leg of male. 96: left paramere. 97, 98: endosomal sclerites, lateral and dorsal views. 99: abdomen of female, ventral view (94, 95 same scale; 96–98 same scale).

Figs. 91–93.Metrocoris inthanon, variations of male parameres. 91: specimen from Vietnam, Nghe An Prov., Pu Mat Nature Reserve (CL 4388). 92: specimen from Laos, Vientiane Prov., Ban Van Heue. 93: specimen from Vietnam, Gia Lai Prov., 60 km N. of An Khe (CL 4309).

Figs. 123–130. Morphological features of Metrocoris tenuicornis. 123: right fore leg of male. 124–126: right paramere of lectotype. 127, 128: left paramere of specimen from Vietnam, Quang Binh Prov. (124, 127: outer view; 126, 128: inner view; 125: apex of paramere, caudal view). 129: endosomal sclerites of lectotype, lateral view. 130: sternum 7 of female, ventral view.

Figs.131–136. Metrocoris tenuicornis, variations of male parameres. 131: specimen from Myanmar, Maymyo (CL 4012).132: specimen from Vietnam, Hai Hung Prov., 23 km N. of Chi Linh (CL 4375). 133: specimen from Vietnam, Lam Dong Prov., 5 km N. of Dalat (CL 3086). 134: specimen from Laos, Vientiane Prov., Ban Van Heue. 135: specimen from Vietnam, CL 4309, Gia Lai, 60 km N. of An Khe (CL 4309). 136: specimen from Cambodia, Koh Kong Prov., 31 km NE. of Koh Kong (CL 6021).

Figs. 100–107. Morphological features of Metrocoris nigriventris, new species. 100: right fore leg of male. 101–103: left paramere, three different views. 104, 105: endosomal sclerites, lateral and dorsal views. 106: hind coxa and trochanter of female. 107: sternum 7 of female, ventral view (101–105 same scale; 106, 107 same scale).

Figs. 108–116. Morphological features of Metrocoris monticola, new species. 108: right fore leg of male. 109: proctiger of male. 110–112: left paramere, three different views. 113, 114: endosomal sclerites, lateral and dorsal views. 115: hind coxa and trochanter of female. 116: sternum 7 of female, ventral view (110–114 same scale; 115, 116 same scale).

Figs. 117–122. Morphological features of Metrocoris sapa, new species. 117: right fore leg of male. 118: left paramere. 119, 120: endosomal sclerites, lateral and dorsal views. 121: hind coxa and trochanter of female. 122: sternum 7 of female, ventral view (121, 122 same scale).