1. Gills: Water snails possess gills, which are specialised respiratory organs that extract oxygen from water. Gills are highly vascularised and create a large surface area for efficient oxygen uptake, allowing snails to breathe underwater.
2. Lung Cavity: Some water snail species, such as the common pond snail (Lymnaea stagnalis), have a modified mantle cavity that functions as a lung. This lung cavity allows them to breathe atmospheric air when they come to the water's surface occasionally.
3. Siphon: Certain water snails have a respiratory siphon, which is a tube-like structure that extends from their body. This siphon allows them to extend their respiratory opening to the water's surface for air exchange, even when the rest of their body is underwater.
4. Anaerobic Metabolism: Some water snails can switch to anaerobic metabolism under low oxygen conditions. This allows them to survive for some time without direct access to oxygen by producing energy through the breakdown of stored glycogen without using oxygen.
5. Air Stores: Some water snails have the ability to store air in their shells or mantle cavity. By trapping air bubbles, they can maintain a small oxygen reservoir, which helps them stay submerged for longer periods.
6. Operculum: Many water snail species have an operculum, a trapdoor-like structure that seals the opening of their shell when they retract inside. This adaptation helps snails conserve water and oxygen, allowing them to remain submerged for extended periods.
7. Aquatic Body Plan: Water snails have streamlined and often rounded body shapes that reduce water resistance and make it easier for them to move efficiently underwater.
These adaptations, combined with their ability to regulate their buoyancy and tolerate varying oxygen levels, allow water snails to thrive in aquatic environments and survive while staying underwater for extended periods.