Orthetrum agaricum Dijkstra

Dijkstra, Klaas-Douwe B., Kipping, Jens & Mézière, Nicolas, 2015, Sixty new dragonfly and damselfly species from Africa (Odonata), Odonatologica 44 (4), pp. 447-678 : 632-636

Orthetrum agaricum Dijkstra sp. nov. – Western Mushroom Skimmer (Type Photo 50, Photos 65–66, Fig. 31)

Taxonomy

Although their morphology did not initially suggest it, three new Orthetrum species first recognised in the field were found to be genetically close to each other and O. saegeri Pinhey, 1966 ( Tree 8). The latter species itself comprised of two geographically distinct groups, which differ in details of the hamule and markings. All species in this saegeri -group are rather small and slender, occurring locally in cooler (shaded or elevated) habitats with much organic material (e.g., peat moss, leaf litter) and little open water.

Material studied

Holotype ♂. RMNH.INS.501573 , Liberia, Grand Gedeh County, Putu Iron Ore Mining concession, 3 km south of Slabbertsville camp , sandy stream in rainforest, 233 m a.s.l. (5.6366 ° N 8.1674 ° W), 03-ii- 2011, leg. K.-D.B. Dijkstra & A. Dayeker, RMNH .

Further material. GHANA (Eastern Region): 1 ♂, N of Kibi, Atewa Range Forest Reserve, Obeng-ne-obeng stream , 637 m a.s.l. (6.2342 ° N 0.5675 ° W), 20 -vi- 2006, leg. K.-D.B. Dijkstra, RMNH . LIBERIA (Grand Gedeh County): 4 ♂, as holotype, RMNH . 1 ♂, as holotype, CJKL . 1 ♂ ( RMNH.INS.501520 ), Putu Iron Ore Mining concession, Biodiversity Camp , sandy and gravelly streams and muddy seepage in rainforest, 299 m a.s.l. (5.6592 ° N 8.2041 ° W), 22 -i- 2011, leg. K.-D.B. Dijkstra & A. Dayeker, RMNH . 1 ♂, Putu Iron Ore Mining concession, swamp south of Mt Montroh , dammed swamp and feeder stream and springs in rainforest, 215 m a.s.l. (5.6845 ° N 8.1392 ° W), 14 -ii- 2011, leg. K.-D.B. Dijkstra & A. Dayeker, RMNH . LIBERIA (Nimba County): 1 ♀ ( RMNH.INS.504213 ), Mt Tokadeh, north of corner swamp, road edge in rainforest , 676 m a.s.l. (7.4661 ° N 8.6650 ° W), 20 -iii- 2011, leg. K.-D.B. Dijkstra, RMNH .

Genetics

Three unique haplotypes (n = 3) with no evidence that this species is nearer to O. saegeri than to other species in the group ( Tree 8).

Male morphological diagnosis

Nearest to its eastern counterpart O. saegeri by (a) moderate size, Hw 29.5– 30.5 mm (n = 7); (b) the absence of cell-doublings in the radial planate and thus a single row of cells there; (c) all subcostal Ax dark; (d) the mediumsized dark brown Pt that are 10–11 % of Hw length, 3.0– 3.3 mm; (e) Hw base faintly yellow, but never with a dark brown patch; (f) the slender abdomen, though shorter than Hw; and (g) the hamule excised anteriorly, with expanded hood- or mushroom-like hook that is turned outward, hugging and often partly concealed by the lobe ( Fig. 31). When not pruinose also similar by (h) the dorsa of S 4–6 bearing pairs of pale subapical spots that lie closer to the dorsal than lateral carinae, while the appendages often remain pale. However, (1) the anterior excision at the base of the hood-like hamule hook has a straight rather than sigmoid profile; and (2) the out-turned part of the hamular hook is less than twice as long as wide in ventral view, rather than well over ( Fig. 31). When not pruinose also (3) only S 4–6 have distinct pale subapical spots and S 7 is black at most with hint of a spot, while O. saegeri typically has a similar spot there as on S 4–6.

Etymology

Latinised form of the Greek agarikon (“mushroom”) refers to the distinctive shape of the hamule’s hook (noun in apposition).

Range and ecology

Replaces O. saegeri from Liberia to Ghana and possibly also Nigeria, recorded at similar rainforest habitat between 200 and 700 m a.s.l ( Map 11). Males were either found flying rapidly over streams or perching by shaded swamps with much detritus.