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What role do gill slits play in tunicate feeding?

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Bright blue sea squirt Rhopalaea crassa with yellow-edged openings grows on a coral reef among various corals in the Philippines. — tunicate Blue spot sea squirt (*Clavelina moluccensis*), a colonial tunicate.

In tunicates, the gill slits are essential components of their filter feeding mechanism. Beating cilia located on these slits draw a continuous current of water into the mouth and through the pharynx.1

As water passes through, a sheet of mucus—secreted by the endostyle—filters out suspended food particles. The cilia lining the pharynx then move this food-rich mucus sheet upward over the gill slits. Once collected, the mucus is rolled up and transported to the gut for digestion, while the filtered water exits the body through the atrial opening.1