A new, widespread genus of Baetidae from South Asia (Insecta, Ephemeroptera).

Material collected on different islands across South Asia revealed a new genus of Baetidae with a widespread distribution, Arcobaetis gen. nov. The larvae present important similarities with Nigrobaetis , but have paraglossae dorsally with an arc of long, spine-like setae in distal area; long, slightly feathered setae between prostheca and mola of both mandibles; and very slender legs with row of short setae at dorsal margin of femur. The male imago has an extraordinarily small 3 rd (apical) segment of gonostylus, which is much narrower than the apex of the 2 nd segment. The new genus includes five species: A.sumbawensis sp. nov. is described from Sumbawa (Indonesia) based on larvae, A.sumatrensis sp. nov. from Sumatra (Indonesia) based on larvae, A.bornensis sp. nov. from Borneo (Brunei) based on larvae, and A.sripadai sp. nov. (type species) is described from Sri Lanka based on a reared male imago with its larval and subimaginal exuviae; A.gracilentus (Chang & Yang, 1994), comb. nov. from Taiwan, formerly described in Margobaetis Kang & Yang, 1994, a subgenus of Baetis Leach, 1815, and subsequently transferred to the genus Nigrobaetis Kazlauskas (in Novikova & Kluge), 1987, is transferred to the new genus. A key to the larvae of all species is provided. Morphological similarities and the relationship of the new genus to other genera of Baetidae are discussed.