How does gas exchange occur in the lancelet?

Gas exchange in lancelets occurs primarily through their skin and gills. As water flows over the gill slits, oxygen diffuses from the water into the lancelet's blood, while carbon dioxide diffuses from the blood into the water. This process is facilitated by the lancelet's position in the water and its constant movement, which helps maintain a flow of water over the respiratory surfaces. Overall, the thin-walled gills and skin provide a large surface area for efficient gas exchange.