A new Bornean species of Drepanosticta allied to D. actaeon Laidlaw, with notes on related species (Odonata: Zygoptera: Platystictidae)

Drepanosticta kosterini sp. nov. (holotype ♂, from Gunung Penrissen, Kuching Division, Sarawak, Malaysian Borneo, deposited in RMNH) is described from both sexes. It is the sister species of D. actaeon Laidlaw, 1934; a fresh description of the male of D. actaeon and the first description of the female are given, along with discussion of variation in this species. Both D. actaeon and D. kosterini are considered to belong to a species group also including D. rufostigma (Selys, 1886) and a preliminary discussion of variation in this species is given, along with illustrations of both sexes. A neighbour joining COI gene tree for D. actaeon and D. kosterini is presented. The relationships of D. actaeon, D. kosterini and D. rufostigma to other members of the Platystictidae are briefly discussed.