Ophiogomphus (Ophionurus) phantoani Ngo & Nguyen 2021, sp. nov.

Ophiogomphus (Ophionurus) phantoani sp. nov.

(Figs 4–11, 14, 15, 17, 19, 24, 25, 32, 33)

Holotype: ♂, Song Thanh National Park (15.5080 N, 107.4720 E, altitude 1105 m), Dak Re Commune, Nam Giang District, Quang Nam Province, central Vietnam, 28.vi.2020, Q.P. Ngo leg.

Paratypes: 1 ♀ (in copula with holotype male), same data as holotype, both in ZCDTU; 1 ♀, Song Thanh National Park (15.3113 N, 107.9097 E, altitude 725 m), Phuoc Kim Commune, Phuoc Son District, Quang Nam Province, central Vietnam, 12.vii.2018, Alisa J. & Thomas W. Donnelly leg., Rosser W. Garrison Collection, USA.

Etymology. The new species is named in honor of Dr. Phan Quoc Toan, a Vietnamese odonatologist, for his great contribution to the knowledge of Southeast Asian Odonata (noun in genitive case).

Description of holotype male

Head (Figs 4, 6, 8). Labium black, labrum black with a pair of greenish yellow markings at dorso-lateralyl; anteclypeus greenish yellow; postclypeus black with a small yellow spot at dorso-laterally; frons broadly marginated with yellow fascia lying interrupted medially with black; antennae black, yellowish basally; vertex black with two rounded prominences near lateral ocelli. Occiput black, prominent centrally.

Thorax (Fig. 4). Prothorax entirely black. Synthorax mostly black with greenish yellow markings; pale antehumeral stripe and not connected with collar stripe; humeral stripe absent; dorsal carina and post-ventral part of mesinfraepisternum with yellow markings; median part of mesepimeron with pale stripe about half as wide as combined black antehumeral and humeral stripes; a small mid-dorsal yellow stripe on metepisternum; metepimeron largely greenish yellow, anterior and ventral borders black.

Legs (Fig. 4). Legs stoutly built, entirely black. Femur and tibia thick and robust with closely set, gradually lengthening spurs apically. Coxa of front legs black with greenish yellow.

Wings (Fig. 4). Wings hyaline, with brown patches at wing base; anal loop 2-celled; nodal index: Ax/Px = 17/18 (FW) and 12/19 (HW); Pt dark brown, 4.5–5 mm length in both wings, covering about 5 or 6-celles.

Abdomen (Fig. 4). Black with greenish yellow markings; S1 with a medio-ventral spot connecting with postventral spot; S2 with two large lateral spots, one on auricle, the other along posterior carina; S3–6 mostly black each with a narrow basal ring; S7 with a basal spot covering about half of the segment; S8–10 entirely black.

Anal appendages (Figs 10, 11). Entirely black; cercus broad basally, narrower apically, gently curving ventroposteriorly, apex hooked with a dorsal small tooth near the base of cercus. Epiproct curved posterodorsally, subequal in length to cerci with a small dorsal tooth approximately at basal third.

Accessory genitalia (Fig. 24). Anterior hamulus broad medially, abruptly attenuate with apical half strongly curved posteriorly. Posterior hamulus broad basally, narrower and slightly curved cephalad at apex.

Vesica spermalis (Figs 14, 15, 25). Prepuce protruded ventroposteriorly, its stem slender; posterior lobe of vesica spermalis slender and short. Cornua of glans with two long, acute V-shaped flagellae (Fig. 25).

Measurements (in mm). Abdomen (including appendages) 40; HW 33.

Description of a paratype female

Colour pattern similar to that of holotype male apart from the following characters:

Head (Figs 5, 7, 9, 17, 32). The greenish yellow markings on dorsal frons much narrower (Fig. 9), (Fig. 8); occiput flattened, a projection medially on occipital crest as shown in Figs. 17 and 32, its dorsal surface minutely serrate.

Thorax (Fig. 5). Prothorax entirely black. Synthorax robust, yellow making same as in holotype but lacking small mid-dorsal yellow patch on metepisternum.

Wings (Fig. 5). Wings hyaline, with dark brown patches at the base; nodal index:Ax/Px = 17/21 (FW) and 12/21 (HW); Pt dark brown, 4.5–5 mm length in both wings, covering about 5–7 cells.

Abdomen (Fig. 5). S1 with lateral triangular patch; lateral S2 laterally with a large greenish yellow marking; S3–6 each with a pale basal ring; anterior fourth of S7 yellow; S8–10 entirely black.

Anal appendages (Figs 19, 33). Cerci as the length of S10, dark yellowish, slender, parallel, pointed at tip. Vulvar lamina triangular-shaped, incised apically but not forming a gap.

Measurements (in mm). Abdomen (including appendages) 30 mm. HW 48 mm.

Differential diagnosis. Among the known species of the genus Ophiogomphus, the new species shares the following characters with O. longihamulus, O. minimus and O. sinicus, i.e. large pincer-like appendages with cerci curving posteroventrally and epiproct curving posterodorsally, with apex notched (Figs 10, 12).

Ophiogomphus phantoani can be distinguished from the other congeners by the following characters: In the male, the cornua of glans has two long, acute widely separated, V-shaped flagella (Fig. 25), whereas they are relatively short, U-shaped flagella in O. longihamulus (Fig. 21), O. minimus (Fig. 23) and O. sinicus (Fig. 27); anterior hamulus of O. phantoani with well-developed developed posterior shoulder (Fig. 24) shoulder smaller in O. longihamulus (Fig. 20), O. minimus (Fig. 22) and O. sinicus (Fig. 26).

In the female, the occiput of O. phantoani has a projection with two prominent dorsally microserrated branches (Fig. 32), more widely branched than in O. longihamulus (Fig. 28), O. minimus (Fig. 30) and O. sinicus (Fig. 34); the vulvar lamina of O. phantoani differs from the other species by a pointed tip (Fig. 33), which is incised apically but not widely opened as in the other species (Figs 29, 31, 35).

Habitat and ecology. Ophiogomphus phantoani was found on a small, slowly running, densely vegetated stream (about 1–2 m wide) within pristine forest. The stream originates from a marsh with muddy bottom. The new species shares the same habitat with Coeliccia schorri Phan & To, 2019; C. scutellum Laidlaw, 1932; Rhinocypha watsoni van Tol & Rozeendal, 1995; Burmargiolestes sp.; Mnais mneme Ris, 1916; Orthetrum glaucum (Brauer, 1865); Anotogaster chaoi Zhou, 1998; Lamelligomphus camelus Martin, 1904 and Merogomphus pavici Martin, 1904.

Distribution (Fig. 36). Vietnam: Quang Nam Province (Song Thanh National Park).