Theodoxus danubialis is a species of small freshwater snail with an operculum, an aquatic gastropod mollusk in the family Neritidae, the nerites.

The species is considered as endangered in Germany, Austria and in the Czech Republic.

The surface has a characteristic dark brown zigzag drawing on a light background.

[4] It occurs in Austria, Bosnia and Herzegovina, Bulgaria, Croatia, Czech Republic (in Moravia it is critically endangered),[5][6] Germany (in Bavaria only and it is critically endangered),[7] Hungary, Italy, Romania, Slovakia,[6] Slovenia, Ukraine, Serbia and Montenegro.

These snails live on hard benthic substrates,[3] typically rocks or stony ground and feed mainly on diatoms.