How do mollusks get oxygen from water?

Most mollusks breathe by drawing oxygen-rich water into their mantle cavity through an incurrent siphon. The water then passes over the gills through a series of ciliary currents, and oxygen from the water is absorbed by the gill filaments. The deoxygenated water is then expelled through an excurrent siphon.

Some mollusks, such as octopuses and squid, have a more complex respiratory system that involves pumping water over the gills through muscular contractions. These animals also have a closed circulatory system, which means that the blood is contained within vessels rather than flowing freely throughout the body cavity. This allows for more efficient oxygen transport and helps to maintain a high metabolic rate.

A few mollusks, such as the shipworm, have no gills and instead absorb oxygen directly from the water through their skin. These animals typically live in burrows or other sheltered environments where the water is relatively still.