Onychargia hungeri sp. nov.

(Figures 7–27, 29, 37–39; 46–50)

Type material. Holotype ♂, swampy wetland near Forest Guard Station No. 4 (10.52238° N, 107.47591° E, altitude 41 m), Binh Chau - Phuoc Buu Nature Reserve, Ho Chi Minh City, 20.vii.2025, M.K. Tran leg. (ZCDTU).

Paratypes. 1 ♀, same data as the holotype; 3 ♂♂, 1 ♀, same location and collector as the holotype, 4.vi.2025; 8 ♂♂, 4 ♀♀, same location as the holotype, 6.x.2025, Q.T. Phan leg. (ZCDTU).

Etymology. The species is named after Holger Hunger from Freiburg, Germany (in genitive case). Holger Hunger has provided nearly three decades of financial support to the International Dragonfly Fund (IDF) and has contributed through his ongoing work on the IDF website (https://dragonflyfund.org/en/) and service as a member of its Editorial Board.

Description of holotype. Head (Figs 9–10). Head and antennae shining black, except for two pale spots located laterally above the upper margin of the postclypeus; mandibles and genae metallic blue; a transverse greyish blue stripe extending from the vertex to the eye margin. Compound eyes in life bicolored: upper part black, lower part turquoise.

Thorax (Figs 10–11). Prothorax black; anterior and middle lobes of pronotum covered with a bluish pruinescence; propleuron with a yellow patch. Synthorax: mesepisternum black with a bluish stripe of pruinescence extending from the coxa of the midleg to posterior of mesepisternum, broad anteriorly and tapering posteriorly (reaching before the posterior end), this pattern forms a U-shaped pruinosed stripe on lateral synthorax; mesepimeron and metepisternum mostly black, with a yellow stripe along the interpleural suture, overlaid with bluish pruinescence; metepimeron and metapimeral carina covered with pale bluish pruinescence. Mesinfraepisternum and metinfraepisternum largely black, with a thin layer of bluish pruinosity.

Legs (Fig. 7) black, with pale yellow markings at the base of coxae; coxae, trochanters, and femora covered with a thin bluish pruinescence. Tibiae, spines and claws black.

Wings (Fig. 7). Wings hyaline, with 9 Px in both FW and HW. Pterostigma light brown, covers one cell.

Abdomen (Figs 7, 37, 38). Black with blue rings at the inter-segmental joints between S2–7 and narrow pale yellowish stripes running along the ventral margins of S3–8. S1 and S8–10 covered with a thin bluish pruinescence. S2 with a large pale-yellow spot laterally (Fig. 7). In lateral view, S10 short, posterior margin strong produced dorsally (Fig. 37); in dorsal view, the posterior margin of S10 features two blunt, prominent protrusions (Fig. 38).

Anal appendages (Figs 15–18). Black with typical shape of the genus. In lateral view (Figs 15–16), cerci shorter than S10 and paraprocts, hook-like, bent downward at the middle; at the angle of curvature a small dorsal spine is present, directed posteriorly; ventral margin deeply concave, cerci apex rounded. Paraprocts broader and longer than cerci, broad at base, tapering toward the apex, and curved inwards. In dorsal view (Fig. 17), cerci incurved, with the small dorsal spine directed outward. In ventral view (Fig. 18), main axis of paraprocts tapering, pointed apex, slightly convergent, ventral lamina of paraprocts black.

Genital ligula (Figs 19–20, 44). Segment 1 short, robust, directly connected to abdomen. Segment 2 large, curved anteriorly, surface smooth without spines or denticles; apex bearing a pair of expanded lateral lobes, resembling a bull’s horn, subtriangular, bilaterally symmetrical, directed outward; lobes thickened, outer margin slightly incurved, anterior margin rounded. Segment 3 (flagella) short, slender, located medially between lateral lobes, difficult to observe in lateral view but visible in ventral view.

Measurements (in mm). Total length 26; HW 14.5; abdomen (including appendages) 20.5.

Description of paratype female. Head (Figs 12–13). Labrum pale yellow, upper margin with a black spot, lower margin black; mandibles and genae pale yellow, the yellow mark extends from the margin of the eyes, forming an arched band above the postclypeus, and ending at its upper margin; anteclypeus yellow with black markings on the lower lateral margins; postclypeus yellow with a large black patch along the upper border.Antennae black, except the base of the first segment which is yellow. Anterior and posterior parts of head black with a broad transverse pale yellow band extending from vertex to eye margin. Compound eyes in life bicolored: upper part black, lower part pale bluish-white (Fig. 26).

Thorax (Figs 13–14). Prothorax: anterior lobe of pronotum black. Middle lobe deeply emarginate anteriorly, posterior margin slightly undulate, dorsal surface more elevated than that of anterior lobe, slightly concave laterally, with an arcuate ridge extending from the anterior margin of the posterior lobe to the anterior margin of the propleuron. Middle lobe largely black with yellow markings laterally adjacent to the propleuron. Propleuron slightly swollen, yellow. Posterior lobe black, divided into three parts: a large central portion and a small process on each side. Central portion shield-shaped, corners rounded, oriented longitudinally, with an arcuate ridge on its anterior margin. Lateral processes narrow, shorter than central portion, apex pointed and slightly curved ventrally. Synthorax black with a narrow yellow stripe on mesepisternum (not reaching the dorsum), broad anteriorly and tapering posteriorly. A yellow stripe present between mesepimeron and metepisternum, covering the spiracle. Metepimeron, metapimeral carina, lower part of mesinfraepisternum and metinfraepisternum also yellow.

Legs (Fig. 8). All coxae mostly black with a yellow patch laterally. Trochanters yellow ventrally and black dorsally. Femora black with yellow base and a yellow ventral stripe. Tibiae black ventrally, white dorsally. Spines and claws black.

Wings (Fig. 8). Wings hyaline, with 10 Px in forewing and 9 Px in hindwing. Pterostigma light brown, covers one cell.

Abdomen (Figs 8, 21–22). Dorsum black: S1 with large pale yellow lateral markings; S2 black broad basally, narrowing towards apex. S3–7 dorsally black with lateral pale stripes: broad on S3–4, narrower on S6, and very narrow on S7. S8 with pale marking only on ventral surface; S9–10 almost entirely black. Lateral pale stripes bluish-white in live specimens, pale yellow in preserved ones. Cerci small, simple, conical, black with apices dark brown. Ovipositor not exceeding paraprocts; visible portion of gonapophyses dark yellow; valvifers with a large pale-yellow area; valvae black with pale yellowish apices; styles black but pale-tipped.

Measurements (in mm). Total length 25; HW15; abdomen (including appendages) 20.

Morphological variation of paratypes. Paratypes show slight morphological variation compared to the holotype and the described female paratype: one male paratype has abdomen (including appendages) 21 mm and HW is 14 mm; another male paratype has 19.5 mm of abdomen (including appendages) length and HW is 15 mm. The other female paratype has 9 Px in both wings, abdomen (including appendages) is 19.5 mm and HW is 15 mm.

Differential diagnosis. Males and females of O. hungeri are significantly smaller in body size compared with O. atrocyana and O. priydak (♂, total length 26 mm vs. 31–34 mm; ♀, total length 25 mm vs 30–32 mm). In coloration, fully mature males of O. hungeri can be distinguished from congeners by the following characters: (1) a pale-purple transverse stripe present on the head dorsum (Fig. 10) (vs. head dorsum entirely black in O. atrocyana and O. priydak (Figs 1, 5)); (2) bluish pruinosity on the prothorax, synthorax, and coxae, along with a characteristic U-shaped stripe on the lateral synthorax (Fig. 10) (vs. only slight pruinosity on the synthorax of O. atrocyana (Fig. 1) or entirely pale bluish white pruinescence on the prothorax and synthorax of O. priydak (Fig. 5)); and (3) abdominal segments S8–10 pruinose white (Fig. 25) (vs. entirely black in both O. atrocyana (Fig. 1) and O. priydak (Fig. 5)).

In lateral view, the posterior part of dorsum of S10 bear two strong blunt processes in O. atrocyana and O. priydak (Figs 31, 34), whereas in O. hungeri they are reduced to small tubercles (Figs 37). The male anal appendages also show diagnostic differences. In lateral view, the cerci of O. hungeri are similar to those of O. atrocyana, equal in length to S10 but shorter than the paraprocts, and slightly curved downward apically; and the paraprocts are pointed at the tips (Figs 31, 37). In contrast, in O. priydak the cerci are shorter than both S10 and the paraprocts, and the paraprocts are blunt at the tips in lateral view, because of some dorsal subapical tubercle (Fig. 34). In ventral view, the paraprocts of O. hungeri have broad bases, inner margins weakly concave, and form a relatively wide inter-lobe gap (Fig. 39), whereas in both O. atrocyana and O. priydak the paraprocts are strongly curved outward apically, forming sharp hook-like tips (Figs 33, 36).

The paraproct upper lamina of O. hungeri and O. priydak has a roundish swelling just above the base of paraprocts (Figs 34, 37) whereas this lamina of O. atrocyana bears two sharply pointed tubercles (Fig. 31).

The valvules (ventral structure of S9) are also diagnostic: in O. atrocyana they consist of two opposing, leaf-like lobes with pointed distal ends and rounded bases, mirrored along the midline (Fig. 33); in O. priydak they consist of two adjacent, subquadrangular lobes with angular margins, each with a broad base narrowing toward the distal end and straight to weakly concave edges (Fig. 36); and in O. hungeri they are composed of two broad, subcircular lobes arranged vertically, with evenly rounded margins (Fig. 39).

Genital ligula of O. hungeri is characterized by having two broad, asymmetrically curved lobes forming a “buffalo horn”-shaped apex (Fig. 44) whereas in O. atrocyana and O. priydak, the apical lobes are broadly rounded (Figs 40, 42). In O. atrocyana, apex of apical lobes gently rounded, with inner margins forming a shallow median concavity (Fig. 40) while the apex slightly concave medially but not sharply divided in O. priydak (Fig. 42).

Apart from the differences in the body size, females of the three species are generally similar, and no reliable structural characters could be identified. We found a small difference in the ear-like structures adjacent to the posterior pronotal lobe of prothorax: in O. atrocyana and O. priydak, they are broad (Figs 41, 43) but those are small-sized in O. hungeri (Fig. 45). Besides, based on field photographs, females of O. hungeri can be separated from those of O. atrocyana and O. priydak by having pale bluish stripes on the thorax and abdomen (Fig. 26) rather than yellowish markings (Figs 4, 6).

Habitat and ecology

The type locality is a lowland site having perennial stagnant water within primary forest, shaded by dense vegetation that maintains moisture and water availability throughout the dry season (Fig. 28). Adults are most active in the morning, prior to midday, and usually move only for short distances between perches located less than 2 m above ground. The breeding season begins in May with the onset of the first monsoon rains and continues until October. Following copulation, females oviposit into leaf litter or submerged plant roots (Fig. 29). Emergence of teneral occurs in April and October (Figs 23–24).

The new species was found synoptically with other damselflies including O. atrocyana, Coeliccia rolandorum Kosterin & Kompier, 2017, Ceriagrion cerinorubellum (Brauer, 1865), Copera vittata (Selys, 1863), Pseudocopera ciliata (Selys, 1863) and Podolestes coomansi Lieftinck, 1940.

Distribution. Ho Chi Minh City (Binh Chau-Phuoc Buu NR.) (Fig. 51).

Notes on ontogenetic changes in body color in male of Onychargia hungeri

Similar to O. atrocyana (while changes in body coloration with age were not observed in O. priydak), males of O. hungeri undergo distinct ontogenetic changes in coloration during maturation. The immature and intermediate stages are described below, based on the progressive development of pruinosity on the male synthorax:

• Early immature stage (Fig. 23). Synthorax brownish with a broad pale bluish stripe on the mesepisternum; abdomen cream-white with black at the base of each segment; anal appendages creamy white.

• Intermediate immature stage (Fig. 24). Synthorax darker, bearing a short whitish antehumeral stripe; abdomen black with white markings on S3–4; anal appendages dark yellow.

• Mature stage (Fig. 25). Prothorax and synthorax black with pale bluish pruinose stripes; antehumeral stripe connected to mesepisternal stripe, forming a U-shaped marking on lateral synthorax; dorsum of S8–10 pruinose white; anal appendages entirely black.