Pseudagrion enganoense (Lieftinck, 1948)

Pseudagrion enganoense , P. igneum , P. nigrihumerale , P. obscurum , and P. simalurum

Lieftinck (1936, 1948) described three subspecies of P. pilidorsum from the islands west of Sumatra, all far away from the nearest known localities of P. pilidorsum . We elevate these subspecies to species level, and together with both new species from the Andaman and Nicobar Islands erected in this paper, there are five species known to occur along the island chain west of Sumatra towards the Andaman Islands yet—each apparently endemic to a single island or a small group of adjacent islands. All of them clearly differ from P. pilidorsum in the pattern of colouration as well as in the morphology of the male appendages, and they differ from P. pruinosum in pattern and the absence of extensive pruinosity. However, among these five taxa the differences are less. Pseudagrion enganoense and P. nigrihumerale are the most unique species as they differ from the others by distinctness in the shape of the male appendages ( P. enganoense ; Figs 136a–c) or by the black humeral stripe and the lack of red at the vertex ( P. nigrihumerale ; Figs 49, 53). Both, P. enganoense and P. nigrihumerale also differ from the other three species by the absence of black on the dorsum of S1–2 ( Figs 31, 49, 119a, b, 122a, b). However the differences between the Andaman P. igneum in the north, and P. obscurum and P. simalurum in the south, are very slight in the male cercus ( P. igneum ; compare Figs 138c, 140c, 141c), as well as in the colour pattern of the pterothorax and the head (see also table 2). Of these species, P. obscurum and P. simalurum are the most difficult to separate as there are no differences in the male appendages although there seem to be clear differences in the colour markings of the head ( Figs 59, 76, 89a, 90), and especially of the dorsum of the pterothorax ( Figs 59, 76, 106, 107). We cannot judge whether the obscurely blackish pterothorax and head in P. obscurum might be just due to older age of the specimens or represent a specific character. There is however only a limited amount of specimens available for these taxa and further material may reveal that they are conspecific. But currently we propose to consider both as different taxa on species rank.