New earthworm species of the genus Amynthas Kinberg, 1867 from Thailand (Clitellata, Oligochaeta, Megascolecidae)

Four new species of terrestrial earthworms from the zebrus-group in the genus Amynthas Kinberg, 1867, are described from Nan province, north Thailand: A. phatubensis sp. n., from Tham Pha Tub Arboretum, A. tontong sp. n., from Tontong Waterfall, A. borealis sp. n., from Chaloemprakiat district, and A. srinan sp. n., from Srinan National Park. After comparing with the two closely related Laos species A. chandyi Hong, 2008 and A. namphouinensis Hong, 2008, the four new species show clear morphological differences, and also it is confirmed that there are no previous records of the species described here. Amynthas phatubensis sp. n. is the largest (longest) sized of these earthworms and is the only species that lives in limestone habitats. The genital characters are different among them and also from the two Laotian species. Molecular systematics would be a good method for further analysis of the diversity and species boundaries in SE Asian Amynthas.