A New Species of the Tiny Tree Snail Genus Sitala H. Adams, 1865 (Gastropoda, Eupulmonata, Helicarionidae) from Northeastern Thailand

A new species of the tiny tree stylommatophoran snails in the genus Sitala H. Adams, 1865, is described based on specimens recently discovered in dry evergreen and dry dipterocarp forests on limestone hills and in agricultural plantations near limestone hills in Loei Province, northeastern Thailand. The new species is characterized by a high, pyramid-shaped, thin, and translucent yellowish-brown shell with a sharp peripheral keel. Although its external shell morphology resembles that of Sitala liricincta (Stoliczka, 1871), the new species can be distinguished by its greater number of whorls (9¼). Comparative anatomical analysis further revealed significant interspecific differences in genital organs, particularly in the length and shape of the vagina, and in the proportions of the penis, epiphallus, and penial caecum. This discovery is the first verified record of the genus Sitala in Thailand.