Green algae
These animals live on stones, and often also under stones, in up to 5–6 m depth or deeper, feeding on algal covers. "Theodoxus " needs rough surfaces in order to be able to digest its food, so a stony substrate is necessary. Green algae are not consumed; "Theodoxus " has no cellulases. These snails lay egg capsules containing 30-70 eggs each, usually on the shells of other "Theodoxus " animals; only one juvenile grows, the other eggs serve as food.