Zospeum tholussum is a cave-dwelling species of air-breathing land snails in the family Ellobiidae. It is a very small species with a shell height of less than 2 mm (0.08 in) and a shell width of around 1 mm (0.04 in). Z. tholussum individuals are completely blind and possess translucent shells with five to six whorls. The second whorl of their shells has a characteristic dome-like shape. They are also extremely slow-moving and may depend on passive transportation through running water or larger animals for dispersal.