Orthetrum erythronigrum, Subramanian & Babu & Kalkman, 2020

Subramanian, K. A., Babu, R. & Kalkman, V. J., 2020, Orthetrum erythronigrum sp. nov. (Odonata: Libellulidae) from the Great Nicobar Island, India, Zootaxa 4869 (2), pp. 242-250 : 243-249

Orthetrum erythronigrum sp. nov.

( Figs. 1–4 & 7–20 )

Holotype ( Figs.1–2 , Map 1): ♂ ( ZSI-SRC I/OD/2265); Wet collection in alcohol. India, Andaman and Nicobar Islands, Great Nicobar Island, Great Nicobar Biosphere Reserve , East-West Road , N 6.99067°, E 93.871363° (Map 1); Evergreen forest ; Alt : 192 m; 01-xii-2018; Time: 7.48 AM ( IST). Leg. K.A. Subramanian.

Paratypes: 1 ♂ ( ZSI-SRC I/OD/2266) same data as holotype ; 1 ♂ ( ZSI-SRC I/OD/2311); Dry collection. India, Andaman and Nicobar Islands, Great Nicobar Island, Great Nicobar Biosphere Reserve , Lakshmi Nagar , N 6.8927°, E 93.8832°; Evergreen forest ; Alt : 35 m; 25-xi-2010, Leg. Padma . 1 ♂ ( RMNH.INS. 1152970) India, Andaman and Nicobar Islands, Great Nicobar Island, Campbell Bay , 23-xii-1996, leg. K. Veenakumari, ex. coll. M. Hämäläinen, RMNH ( Fig. 3 ) ; 1 ♀ ( RMNH.INS. 1152971), Great Nicobar Island, Campbell Bay, upper road (= East-West Road ), 17-xii-1996, leg. K. Veenakumari, ex. coll. M. Hämäläinen, RMNH ( Fig. 4 ) .

Etymology. The species epithet “ erythronigrum ” is named after the unique crimson (erythro is Latin for red) and black (nigrum is Latin for black) colour pattern of the male abdomen.

Description of holotype ( Figs. 1–2 & 7–20 ). Head ( Fig. 7 ), including labium, mandibles, labrum, postclypeus, antennae, occipital triangle and the vertex, completely deep black; the only exception being the anteclypeus which is paler and has a yellowish-black colour. Eyes black (slightly paler than remainder of head) in life and in preservation; ocelli black with light brown rim.

Thorax. Prothorax black, posterior lobe erect with long black hairs ( Fig. 8 ). Pterothorax black without any markings but some blackish-blue pruinescence. Legs black, with short spines; coxae, trochanters, femora, tibia and tarsal segments black ( Fig. 2 ).

Wings ( Figs. 10–11 ) hyaline and enfumed with pale brown towards the apices and posterior borders, venation black. Fw without any basal markings; Hw with slight basal amber markings extending one or two cells. Pterostigma black, long, slightly swollen, covering two cells in Fw and Hw. Nodal index: Fw: 11-17/17-11; Hw: 11-14/14-11. Triangles of all wings with a single crossvein; supratriangle in Fw and Hw with single crossvein. Discoidal field in Fw with three rows of cells and two in Hw. Hw with membranule black and anal loop with 30 cells. Four cells doubled between Rspl and IR3.

Abdomen. S2–3 swollen ventrally, S4–S10 slender; S1–S10 black with some blackish-blue pruinescence dorsally, marked with bright crimson as follows: S3 basolaterally bright crimson, S4–S8 bright crimson ventrally in life ( Fig. 1 ) and dull crimson or yellowish in dry specimens ( Figs. 2 , 12 ). Anal appendages black, covered with short black hairs. Cerci long, about twice the length of S10, broad at base, concave on the inner side, downwardly curved and expanded at centre, upturned and pointed apically. The cerci are directed laterally, which may be a post mortem change. Paraproct shorter, about 2/3 length of cerci, broad at base, oblong shaped when viewed ventrally and upturned apically ( Figs. 13–19 ). Secondary genitalia black, lamina anterior with black hairs, directed backwards, bluntly pointed terminally; hamule with deep median cleft and consisting of two lobes, apices of anterior and posterior parts rounded; genital lobe evenly rounded, with dense longer setae ( Figs. 9 , 20 ).

Measurements: Right Fw: 36; Left Fw: 36; Right Hw: 37; Left Hw: 37; Abdomen with anal appendages: 30.

Paratype: 2 ♂♂ (ZSI-SRC I/OD/ 2266, 2311) and 1 ♂ (RMNH.INS. 1152970) Colouration of head, thorax, abdomen, legs and anal appendages similar to holotype.

Measurements ZSI-SRC I/OD/ 2266: Right Fw: 36; Left Fw: 36; Right Hw: 36; Left Hw: 36; Abdomen with anal appendages: 30; ZSI-SRC I/OD/ 2311: Right Fw: 35; Left Fw: 35; Right Hw: 36; Left Hw: 36; Abdomen with anal appendages: 32.

Female. ( Fig. 4 ). Head. Completely deep black with the exception of the anteclypeus which is yellowishbrown, eyes dark brown.

Thorax. Prothorax mostly black but posterior lobe brown bordered at the sides with black margin and beset with long black hairs. Pterothorax black, mottled with poorly defined brownish pattern. Areas adjacent to the middorsal carina pale forming a broad central stripe on the front of the Pterothorax. Legs largely black but femora partly dark brownish.

Wings. Wings hyaline with black venation and slight yellowish tinge on base of Fw and a slightly larger yellowish area on base of Hw; membranulae black. Pterostigma blackish brown, long covering two cells in Fw and little more than one cell in Hw. Nodal index: Fw: 12-17/17-12; Hw: 13-13/13-13; last antenodal complete. Triangles of all wings with a single crossvein; supratriangle in Fw and Hw with single cross vein. Discoidal field starts with three cells in Fw and two cells in Hw. Hw with anal loop containing 27 cells. Four to five cells doubled between Rspl and IR3.

Abdomen. S2–S3 swollen ventrally and laterally, gradually tapering towards S4–S5 making the abdomen much more sturdy than in the male. S1, basal part of S2 and the whole of S8–S10 black, remainder of abdomen including venter reddish yellow with black markings on mid dorsal and lateral carina as follows: posterior corner with a black triangle on each side of the mid dorsal carina and a similar mark on the venter of S2–S7 directly along the lateral carina. S8 expanded ventrally. The sides of S7–S10 are laterally compressed in the specimen studied due to which the vulvar scale is poorly visible; as far as can be judged the vulvar scale is small with a simple rounded shape, without incision.

Differential diagnosis. The wing venation (especially the number of Ax with the last Ax being complete), the general shape of the body, the shape of the appendages and the secondary genitalia all match with that of the genus Orthetrum and rule out other genera known from the area. The colouration of O. erythronigrum sp. nov. is, however, strikingly different to that of other species of Orthetrum . The almost completely black head and thorax are reminiscent of that of mature males of O. triangulare (Selys, 1878) but that species has extensive parts of its abdomen blue with pruinosity, lacks the unusual crimson colour and has a differently shaped abdomen.

The mature male of O. erythronigrum sp. nov. is uniquely coloured and can easily be distinguished from all other Orthetrum species and in fact all other species occurring in this part of the world by its almost completely black head, thorax and abdomen of which the later has the venter and the lower sides of S2 contrasting crimson. Female is also easy to identify based on the combination of the large size, the black (non-metallic) head, the largely black thorax and the largely red abdomen with a distinct black pattern. Only two other species of Orthetrum , O. sabina and O. pruinosum neglectum , are known from the Nicobar islands ( Nandy & Babu 2012) and females of these species are very different in morphology and colouration from Orthetrum erythronigrum sp. nov. Other similar looking species Lathrecista asiatica (Fabricius, 1798) and Agrionoptera insignis (Rambur, 1842) occurring in the area are slender but in the former species thorax is dark with pruinosity, parts of the face pale, S8 red and in later, the face is partly pale with a blue metallic frons.

Map 1. Distribution map of Orthetrum erythronigrum sp. nov.

Habitat and Ecology. All four specimens including the female of O. erythronigum sp. nov. were collected from East-West road. The type locality is a forest path (East-West road) within the Great Nicobar Biosphere Reserve traversing through an evergreen forest ( Fig. 6 ). KAS observed one male perched on a fern with its face directed towards a sunlit rainwater pool. Upon being disturbed the dragonfly flew swiftly away, not returning to the same perch like species of Orthetrum generally do. This individual could not be photographed or collected. Further, down the same path, three individuals were found in a similar habitat and were competing for a sunlit perch at a rainwater pool. These individuals were also very fast flying and returned to the perch after ten or more minutes; only two individuals were collected. A detailed search in the vicinity and nearby stream did not yield females or additional male specimens. No habitat information is available on other specimens. One male specimen was photographed by Rajesh Kumar on 20.02.2016 from 18th Km forest area near Vijaya Nagar (N 6.9670°, E 93.9196°; Evergreen forest; Alt: 87 m); Great Nicobar Island ( Fig. 5 ). The species is collected and photographed from last week of November to February.

Figures

FIGURES 1–6. 1–5. Habitus of Orthetrum erythronigrum sp. nov.: (1) holotype male field photograph; (2) holotype male, lateral view; (3) paratype male (RMNH); (4) paratype female (RMNH); (5) photograph from Vijayanagar, Great Nicobar by Rajesh Kumar. (6) Type locality showing habitat, East-West Forest path, GNBR.

FIGURES 7–12. Orthetrum erythronigrum sp. nov. holotype male: (7) head, frontal view; (8) thorax, lateral view; (9) secondary genitalia, lateral view; (10) pterostigma of forewing; (11) left hindwing; (12) abdomen lateral view.

FIGURES 13–20. Orthetrum erythronigrum sp. nov. holotype male: (13) terminal abdominal segments, ventral view; 14–20 anal appendages: (14) ventral view; (15) dorsal view; (16) lateral view; (17) dorsal view; (18) ventral view; (19) lateral view; (20) secondary genitalia, lateral view.