Pseudagrion nigrihumerale, Seehausen & Kalkman & Bedjanič, 2025

Seehausen, Malte, Kalkman, Vincent J. & Bedjanič, Matjaž, 2025, Revision of the Pseudagrion red-group occurring in Asia west of Lydekker’s line, with description of four new species (Odonata: Coenagrionidae), Zootaxa 5587 (1), pp. 1-66 : 29-31

Pseudagrion nigrihumerale sp. nov.

Figures: 49 (habitus holotype ♂); 50–52 (S10, caudal appendages holotype ♂); 53 (head holotype ♂); 54 (pronotum holotype ♂); 55 (habitus paratype ♀); 56 (head paratype ♀); 57 (pronotum paratype ♀); 58 (S9–10, ovipositor paratype ♀); 88 (head ♂); 105 (pterothorax ♂); 122a, b (abdomen ♂); 139a–c (caudal appendages ♂).

Pseudagrion pilidorsum : Rajeshkumar et al. (2016): 45, Fig. 2H ( Nicobar Islands; photo ♂ alive).

Holotype: ♂, 8.i.2001, Munak , Kamorta Island, Nicobar Islands, India, approximately 8.01°N, 93.505°E, Dr Prashant Mohanraj leg., ex. Coll. M. Hämäläinen, no. 1552778. Deposited at Naturalis Biodiversity Center Leiden, the Netherlands.

Paratypes (8♂♂, 3♀♀): 1♂, 3♀♀, 23.xii.2000, 27 km E–W road, Great Nicobar , India, Dr Prashant Mohanraj leg., ex. Coll. M. Hämäläinen, RMNH, no. 1552782–1552784, 1552786 ;— 3♂♂, 8.i.2001, Munak , Kamorta Island, Nicobar Islands, India, Dr Prashant Mohanraj leg., ex. Coll. M. Hämäläinen, RMNH, no. 1552777, 1552779, 1552780 ;— 4♂♂, 9.i.2001, Agriculture Department Farm , Kamorta Island, Nicobar Islands, India, Dr Prashant Mohanraj leg., ex. Coll. M. Hämäläinen, RMNH, no. 1552774–1552776, 1552881 .

Other specimens: 1♂, 19.xii.1996, Campbell Bay , Great Nicobar, India, ex. Coll. M. Hämäläinen, Wen-Chi Yeh, RMNH, no. 1152932. This freshly emerged male belongs to this new species as well, but was excluded from the type series because of its damaged condition .

Etymology: The name refers to the black humeral stripe on the thorax, a unique character of the revised species of the Pseudagrion red-group occurring in the western range.

Remarks

The colours when alive are adopted from the field photograph of a living male provided by Rajeshkumar et al. (2016: 43, Fig. 2H). Additionally they provide the following data of this species (identified as P. pilidorsum ): 1♂, 18.xii.2015, Near dam, Kamorta, Central Nicobar (8°8.242’N, 93°29.256’E = 8.137367°N, 93.4876°E) ; 1♂, 17.ii.2016, near streams in interior forest, Galathea , Great Nicobar Island (7°0.245’N, 93°54.181’E = 7.004083°N, 93.903017°E) ; 1♂, 1♀, 21.ii.2016; ♀ laying eggs on stream near Laxmi Nagar , Great Nicobar Island (6°56.343’N, 93°53.468’E = 6.93905°N, 93.891133°E) .

Description of holotype male

Head ( Fig. 53, also compare Fig. 88): Labium, mandibles, genae, labrum, anteclypeus, postclypeus, antefrons, and postfrons yellow; colour of postfrons sharply separated from vertex at anterior margin of lateral ocelli; vertex black; median ocellus with a black spot anteriorly, merged with black colour of vertex; occipital bar reddish; postocular spots reddish, bordered by black; rear of head black, but yellowish along the eye margins; base and scape of antennae yellow, following segments ochre-brownish.

Thorax ( Figs 49, 54, also compare Fig. 105): Anterior lobe of pronotum orange-reddish, expanding in centre towards middle lobe, anterior margin black; middle pronotal lobe black, with a centrally divided large orange-reddish patch in the middle, and on either side a large orange-reddish patch dorsolaterally, fusing laterally with orange-reddish colour of anterior lobe; propleuron black above, orange-reddish below and to rear; posterior lobe orange-reddish; apical edge of posterior lobe convex. Pterothorax orange-reddish with a broad black middorsal stripe, and a broad black humeral stripe, narrowed posteriorly; metapleural suture with a small elongate black patch at posterior third; mesinfraepisternum with two-thirds black, in line with black of humeral stripe, lower third of mesinfraepisternum ochre and washed-out yellow-orange; venter of pterothorax pale yellowish. Coxae pale yellowish-ochre; outer side of femora with a washed-out blackish stripe along posterior half; tibiae with blackish along the black spines; tip of tarsi and tarsal claws ochre, washed-out blackish along joints.

Wings ( Fig. 49): Membrane hyaline, slightly tinged yellowish; veins brown to black; 15.5–16.5 px in forewing; 14.0–14.5 px in hindwings; Pt dark reddish-brown, overlying one cell.

Abdomen ( Fig. 49, also compare Figs 122a, b): S1 orange-reddish, with black along its posterior margin; S2 orange-reddish, dorsally with an anvil-like black marking in posterior third, and a washed-out blackish middorsal stripe; S3–8 dorsally black, the black colour expanded to lateral at each posterior end; laterally and each basal annulus pale yellowish; S9 with its anterior half laterally and dorsally orange-reddish, separated by a black middorsal stripe which merges with the black posterior half; the anterior margin of the black colour somewhat serrated; S10 black ( Figs 50, 51).

Caudal appendages ( Figs 50–52, also compare Figs 139a–c): Cercus laterally washed-out brownish, slightly shorter than S10, inferior lobe appears slightly shorter than superior lobe; in lateral view cercus subrectangular, apex with a broad inter-lobe notch; in dorsal view cercus appears narrow; apex of superior lobe of the cercus slightly pointed and curved inwards, a subtriangular interior projection is situated just proximal of the middle of the cercus; a small, tooth-like subbasal interior projection before half-length of the inferior lobe of the cercus, visible in dorsal and dorsolateral views; paraproct pale yellow-ochre, around half as long as cercus; in lateral view subtriangular and tapered with rounded apex; in dorsal view broadly rounded, concave bowl-like; with prominent black tooth at blackish medial edge.

Measurements (mm): Total length (with appendages) 41.2; abdomen length (without appendages) 34.3; hindwing 23.7; forewing 24.6; Pt in forewing 0.9; cercus 0.6.

Variation in paratype males

Head: The reddish occipital bar is reduced in some specimens.

Wings: 14.0–16.5 px in forewing, 12.5–14.5 px in hindwing.

Abdomen: The middorsal marking on S9 does not reach S8, but middle of S 9 in some specimens.

Measurements (mm): Total length (with appendages) 37.8–43.1; abdomen length (without appendages) 31.4– 35.5; hindwing 21.0–24.0; forewing 22.2–25.3; Pt in forewing 0.7–0.9; cercus 0.6–0.7.

Description of female paratypes

Head ( Fig. 56): Labium, mandibles, genae, labrum, anteclypeus, postclypeus, antefrons, and postfrons yellow-orange; postfrons dorsally with a small brownish dot in centre; yellow-orange colour of postfrons sharply separated from vertex at level of anterior margin of lateral ocelli; vertex black; median ocellus with a black spot posteriorly; postocular spots yellow-orange, bordered by black; small orange occipital bar; rear of head black, but yellowish along the eye margins; base and scape of antennae yellow, following segments ochre-brownish.

Thorax ( Figs 55, 57): Anterior lobe of pronotum yellowish, expanding in centre subtriangular towards middle lobe, anterior margin black; middle pronotal lobe black, with a centrally divided large yellowish patch in the middle, and on either side a yellowish spot dorsolaterally, fusing laterally with yellowish of the anterior lobe; propleuron black above, yellowish below and to rear; posterior lobe yellowish; apical edge of posterior lobe convex; bearing two yellowish horns directed towards head, approximately reaching the centre of the middle lobe. Pterothorax orange with posterior margins black; a broad black middorsal stripe; a broad black humeral stripe, narrowed posteriorly; metapleural suture with a small elongated black patch at posterior third; mesinfraepisternum with two-thirds washed-out brownish-black, in line with the black of humeral stripe, lower third of mesinfraepisternum yellowish-ochre; venter yellowish, may be slightly covered with whitish pruinosity. Coxae and legs pale yellowish-ochre; outer side of femora with a washed-out blackish stripe along posterior half; tibiae with blackish along the black spines; tip of tarsi and tarsal claws ochre, washed-out blackish along waists.

Wings ( Fig. 55): Membrane hyaline; veins brown to black; 15.5–16.5 px in forewing; 14.0–15.5 px in hindwings; Pt brownish, overlying one cell.

Abdomen ( Figs 55, 58): S1–2 orange with black markings dorsally; S3–8 dorsally black, laterally and each basal annulus pale yellowish; S9 dorsally black, laterally yellow-orange, this colour expanded dorsally in centre of segment, leaving anterior and posterior margin black; S10 black. Cercus in lateral view straight and tapered, washed-out brownish-black, half as long as S10; paraproct yellow-brownish, short, in lateral view rounded; ovipositor yellowish, almost reaching to the posterior end of S10, two yellow-brownish styles reaching beyond S10; inferior edge of ovipositor bearing several very small teeth.

Measurements (mm): Total length (with appendages) 41.3–41.9; abdomen length (without appendages) 34.2– 34.5; hindwing 24.0–24.8; forewing 25.4–26.4; Pt in forewing 0.9.

Diagnosis

Both sexes of P. nigrihumerale are separated from all adjacent species and also most congeners in this group by the obvious thorax marking, bearing a broad black humeral stripe ( Figs 49, 55, 105). Only three species, namely the Sulawesian P. crocops , P. halmaherae from Halmahera, and P. buenafei from Mindanao, Philippines have a similar broad black humeral marking. Apart from their distant range and the morphological differences in the caudal appendages (compare Figs 131a–c, 133a–c, 137a–c, 139a–c), the males of the latter three species differ from P. nigrihumerale in their colour pattern as well. Beside the name-giving black humeral marking, P. nigrihumerale can be separated from its Andaman congener P. igneum by having S1–2 dorsally red and S10 entirely black ( Figs 43, 49, 121a, b, 122a, b), by having a black vertex and by lacking red colour on the postfrons ( Figs 47, 53, 87, 88), whereas the male appendages of both species are identical ( Figs 138a–c, 139a–c). The southerly distributed species P. simalurum and P. obscurum differ by the same colour markings as listed for P. igneum , but also very slightly in the male appendages: the cercus of P. nigrihumerale bears a small subbasal tooth situated at the proximal third of the inferior lobe, whereas in P. simalurum and P. obscurum there is a sharp edged bulge that only looks like a tooth in dorsal view ( Figs 140a–c, 141a–c).

Distribution

Apparently endemic to the Nicobar Islands, India ( Fig. 2).