Zygonyx dionyx Dijkstra & Mézière ^ZBK sp. nov. –

Eastern Double-hooked Cascader

(Type Photo 60, Photo 26, 56, Fig. 35)

Taxonomy

Part of the flavicosta -complex of Zygonyx Hagen, 1867 (see Z. annika sp. nov.). Genetics and the distinct morphology of its secondary genitalia suggest it is the eastern counterpart of the Upper Guinea endemic Z. geminuncus (Tree 10).

Material studied

Holotype ♂. RMNH.INS.508872, Gabon, Haut-Ogooué Province, Batéké Plateau, Léconi Valley, Eaux Claires, Camps des Pygmés, sandy river (4 m wide, 20–200 cm deep) in gallery forest bordered by swamp, 434 m a.s.l. (1.4549 ° S 14.1785 ° E), 29 -ix- 2013, leg. N. Mézière, J. Kipping & H. Krahnstöver, RMNH .

Further material. GABON (Haut-Ogooué Province): 1 ♂, locality as holotype, 16 -ix- 2012, leg. N. Mézière, RMNH . 1 ♂, Bongoville-Léconi road after Ekala, old village of Boubou, stream (2 m wide) with gravel bottom, 393 m a.s.l. (1.6114 ° S 13.9105 ° E), 17 -iv- 2011, leg. N. Mézière, RMNH . 1 ♂ (RMNH.INS.508075), Batéké Plateau, 18 km NW of Léconi, sandy stream in dense gallery forest, tributary to Léconi River, 425 m a.s.l. (1.447218 ° S 14.166175 ° E), 29 -ix- 2013, leg. J. Kipping, CJKL . 1 ♂, same locality, 30 -ix- - 2013, leg. J. Kipping, CJKL .

Genetics

Two unique haplotypes (n = 3) that are nearest to Z. annika and Z. geminuncus (Tree 10).

Male morphological diagnosis

Belongs to the flavicosta -complex by (a) the modest size, Hw 36.0– 38.5 mm (n = 3); (b) the moderately dense venation, with 11 ½– 12 ½ Ax in Fw; (c) the largely black hind legs; and (d) the pale subapical band on the dorsum of S 7 that stands out against largely dark S 5–6. Most similar to the probable sister-species Z. geminuncus with (e) the apex of the anterior lamina being constricted and incised to form a pair of triangular forward-curved hooks; and (f) the hamule with a low lobe and narrow base making its hook appear longer (Fig. 35). However, (1) the anterior lamina is not swollen and raised laterally of the apical hooks to eclipse them in lateral view; (2) the apical hooks of the the anterior lamina are relatively large; (3) the hamule has a less tapering base; and (4) the epiproct is longer with a narrower tip (Fig. 35).

Etymology

Greek “two claws” in parallel to Latin “twin claw” of western counterpart Z.geminuncus and matching the generic name (noun in apposition).

Range and ecology

Sandy and very clear tributaries of the Léconi River at about 400 to 435 m a.s.l. on the Batéké Plateau in south-eastern Gabon, which meander through dense gallery forest surrounded by open grasslands (Photos 26, 56). As for Z. geminuncus, these sites are much shadier than preferred by other Zygonyx species, including Z. flavicosta, and males hover very low over rapid sections at the few sun spots present.