Vietnamellidae (Insecta, Ephemeroptera) of Thailand.

The genus Vietnamella Tshernova, 1972 is investigated in detail for the first time in Thailand. As a consequence, four species are recognized, namely Vietnamella maculosa sp. nov., Vietnamella thani Tshernova, 1972, Vietnamella sp. B and Vietnamella sp. C. Herein, larvae and eggs of V. maculosa sp. nov. are described and reported from Chiang Rai Province. The larva of Vietnamella sp. B from Tak Province is also described, but not named due to insufficient material, and the imaginal stages and eggs of V. thani Tshernova, 1972 are described and presented for the first time. Our morphological evidence is supported with COI data. The phylogeny showed that four different lineages of the genus Vietnamella occur in Thailand, one of them, viz., Vietnamella sp. C, only known from a couple of COI sequences retrieved from the Barcode of Life Data System (BOLD). Diagnoses for all known Oriental species are also presented.