Taxonomic insights into the diversity of Cloeon Leach, 1815 (Ephemeroptera, Baetidae) in Thailand

Four species of the genus Cloeon have previously been reported in Thailand: C. bicolor Kimmins, 1947, C. bimaculatum Eaton, 1885, C. harveyi (Kimmins, 1947) and C. marginale Hagen, 1858. However, since 1961, no systematic studies or investigations of this genus have been conducted in that country. This study reviews Cloeon Leach, 1815 in Thailand and investigates five species— C. bengalense , C. bicolor , C. harveyi , C. rubellum , and C. viridulum —based on morphological, molecular, and taxonomic analyses. Three species ( C. bengalense , C. rubellum , and C. viridulum ) are recorded for the first time in Thailand, and C. rubellum is described for the first time as a mature nymph and adult female. Additionally, the egg chorionic surface of all five species is described for the first time, and its use is demonstrated for species identification in Thailand. A key to the species of Cloeon in Thailand is provided based on the egg structure, mature nymph, and adult female and male.