Metrocoris sikkimensis, Basu & Chandra & Venkatesan, 2018

Basu, Srimoyee, Chandra, Kailash & Venkatesan, Thiruvengadam, 2018, Metrocoris sikkimensis sp. nov. (Hemiptera: Heteroptera: Gerridae) from northeastern India, with a key to species of the compar group occurring in India, Zootaxa 4471 (2), pp. 369-374 : 370-374

Metrocoris sikkimensis sp. nov.

Type material examined: HOLOTYPE, apterous male (in 75% ethyl alcohol): INDIA, Sikkim, West Sikkim District , hill stream, Kaleg Khola, Pelling road, 27.2956°N, 88.2226°E, alt. 1841 m, 10 May 2016, coll: S. Basu . PARATYPES (in 75% ethyl alcohol):10 apterous males,10 apterous females: same data as holotype; 15 apterous males, 12 apterous females, West Sikkim District, Reshikhola River, Rinchenpong , 27.2441°N, 88.8735°E, alt. 1618 m, 9 May 2016, coll: S. Basu. 8 apterous males, 17 apterous females, INDIA : Arunachal Pradesh, West Kameng District, Rupa river, near Rupa village, Bomdila, 27.20390°N, 92.39420°E, 4804ft, 9 October, 2017, coll: S. Basu; 4 apterous males, 4 apterous females, West Kameng District, Dublekha River, Jigaon, near Rupa village, Bomdila, 27.20840°N, 92.39965°E, 4780 ft, 9 October, 2017, coll: S. Basu; 5 males, 5 females, West Kameng District , Kameng River, Nagmandir, 27.28440°N, 92.82830°E, 1495 ft, 5 October, 2017, coll: S. Basu.

Description. Apterous male ( Figs. 2, 4–6, 7, 9, 10 , 13–17 ).

Size: Body length 5.37, body width across mesoacetabula 2.50.

Colour: Dorsally black with bright yellowish orange markings. Interocular mark on posterior margin of head distinct, yellowish ( Figs. 2, 5 ). Eyes black. Antenna black with yellow basally. Rostrum black with yellowish laterally. Pronotum with a pair of flattened ‘u’ shaped yellowish orange markings ( Figs. 2, 5 ). Meso- and Metanota each with a pair of yellow markings ( Figs. 2, 5 ). Pro-, meso-and metapleura with a longitudinal yellow stripe, discontinuous near posterior margin of pronotum. Mesosternum without yellow markings. Meso- and metacetabula each with a dorsal yellow mark. Fore, mid and hind coxae and trochanters yellow. Fore femur ( Fig. 7 ) black, yellowish basally, dorsally and ventrally. Mid and hind femora, tibiae and tarsi black. Abdominal terga I–VII and proctiger black, tergum VIII black with yellow margins ( Fig. 9 ). Abdominal laterotergites black, except yellow posterolateral angles of last segment. Venter black, except sterna VII–IX yellowish brown ( Fig. 10 ).

Structural characteristics: Head length 0.77, width excluding eyes 0.95, narrower than pronotum. Eyes 2.2 times longer than broad, length 0.62, width 0.28. Minimum interocular width 0.63. Length of antennal segments I– IV= 2.34, 0.73, 0.79, 0.63, first segment longer than combined length of segments II–IV, without spines or bristles. Rostrum reaching to mesothorax, length 1.26. Pronotum 2.8 times wider than long, length 0.47, width 1.35, slightly bulbous. Combined length and maximum width of meso- and metanota 2.26 and 1.77 respectively. Fore femur ( Fig. 7 ) slender, fringed with short setae, slightly constricted apically and with one or two thin small setae basally, ratio of length/width 7.51 (2.33/0.31). Fore tibia and tarsus without modification, but covered with short setae. Pretarsal claws distinct, curved and sharp. Mid and hind trochanters lacking modifications. Abdominal terga densely covered by setae, combined length 2.03, maximum width at tergum V 1.48. Abdominal sterna II–VI with golden pubescence, sterna VII–VIII long, distinctly clothed with long dense golden setae ( Fig. 10 ). For measurements of leg segments see Table 1.

Genitalia: Abdominal sternum VIII ( Figs. 10 , 13 ) short with median inverted U-shaped excavation, blunt at apex, anterior margin emarginated at middle, length 0.79, width 0.65, covered by golden setae, density increasing laterally. Pygophore ( Fig. 14 ) elongated, broadened medially, heavily setiferous, posterior margin almost straight. Proctiger ( Fig. 15 ) elongated, with maximum width near middle, parts of lateral margins anterior and posterior to the protrusion are concave, laterally slightly protruded near middle, apex rounded, clothed with dense setae. Parameres ( Figs. 13, 17 ) symmetrical, projecting laterally from genital segments, curved apically, without setae, apex slightly pointed; in few individuals, parameres not visible from above. Endosomal sclerites ( Fig. 16 ) well developed; dorsal sclerite long, entirely covering the endosomal sheath and extended apically; lateral sclerite almost straight, relatively long; ventral sclerite long.

Apterous female ( Figs. 3, 8 , 11, 12 ). Size: Body length ranges from 5.10–5.39 (n=48), maximum width across mesoacetabula ranges from 2.56–2.62 (n= 48).

Colour: Colour pattern similar to that of male, except yellowish marks much wider and more prominent.

Structural characteristics: Head length 0.74, width (without eyes) 0.89. Length of antennal segments I–IV: 2.18, 0.79, 0.77, 0.69. Eye length 0.64, width 0.37. Minimum interocular width 0.70.Length of rostrum 1.26. Pronotum wider than long, length 0.46, width 1.51. Combined length of meso- and metanota 2.26, maximum width 2.35. Fore femur ( Fig. 8 ) length/width ratio 8.4 (2.45/0.29), without modifications; pretarsi with sharp curved claws. Hind trochanter apically with fringe of setae. Abdominal sterna length 1.36, maximum widths 1.59 at sternum V. For measurements of leg segments see Table 2. Abdominal sternum VII ( Fig. 12 ) more or less oval, constricted laterally, with small lobe, covered by short golden pubescence, length 0.65, width 1.09, posterior margin straight.

Macropterous forms: Unknown.

Etymology. The specific epithet ‘sikkimensis’ derives from its place of origin, the northeastern state of Sikkim.

Discussion. The newly described species belongs to the compar group and can be easily distinguished from congeners by the entirely black venter lacking yellow markings on the meso- and metasterna ( Fig. 4 ); the distinctive shape of male paramere ( Fig. 17 ), which is almost straight in the middle with the apex slightly pointed and without projections; the structure of male endosomal sclerites ( Fig. 16 ) and the male proctiger ( Fig. 15 ); and by the female terminalia, which are ventrally more or less oval, with a small lobe and covered by golden pubescence ( Fig. 12 ).

Recently, Basu et al. (2016) reported a total of 20 species of Metrocoris from India, with a key to all known Indian species. Hence, Metrocoris sikkimensis sp. nov. is the 21 st species described from the country. Within the Metrocoris compar group, M. sikkimensis sp. nov. is closely related to M. hirtus Chen & Nieser, 1993 from China, but differs from the latter as follows. In M. hirtus , surface of the male paramere has a small projection pointing forward and the apex is blunt, whereas in M. sikkimensis sp. nov. the paramere is slightly curved apically and the apex is more or less pointed, without projections or setae. Furthermore, the male pygphore is subovate in M. hirtus , but in M. sikkimensis it is elongated and heavily setiferous and the posterior margin of male pygophore almost straight. Additionally, the male forefemur is slightly constricted apically and has one or two thin short setae basally at the ventral surface in M. sikkimensis , whereas there is no apical constriction or thin basal setae in M. hirtus .

Metrocoris sikkimensis is also similar to M. nepalensis , but can be separated from the latter by the following characteristics: In M. nepalensis , the male paramere bears a small projection pointing dorsally, and by the endosoma with a small accessory apical sclerite, indistinct lateral sclerite, and long ventral sclerite. In contrast, M. sikkimensis does not have a projection on the male paramere, an accessory apical endosomal scleriteis absent, the lateral sclerite is distinct and extends upto the proximal portion of the dorsal sclerite, and the ventral sclerite is long, slender and extends forward.

Figures

FIGURES 2–10. Metrocoris sikkimensis sp. nov. (2) Dorsal view of apterous male; (3) Dorsal view of apterous female; (4) Ventral view of apterous male; (5) Head and thorax of male, dorsal view; (6) Head and part of thorax of male, ventral view; (7) Ventral view of male fore leg; (8) Dorsal view of female fore leg; (9) Meso-, metanota and abdomen of male, dorsal view; (10) Part of thorax and abdomen of male, ventral view.

FIGURES 11–17. Metrocoris sikkimensis sp. nov. (11) Part of thorax and abdomen of female, dorsal view; (12) Part of thorax and abdomen of female, ventral view; (13) Dissected male terminalia; (14) Pygophore of male, ventral view; (15) Proctiger of male, dorsal view; (16) Endosoma of male, lateral view, showing sclerites (ds-dorsal sclerite; ls1-left first lateral sclerite; ls2- left second lateral sclerite; vs- ventral sclerite); (17) Male paramere, lateral view.