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What is the tough outer tunic of a tunicate made of?

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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.

The tough outer tunic of a tunicate is primarily composed of cellulose, a glucose polysaccharide that is typically found in plants rather than animals. This unique substance, sometimes referred to as tunicin or animal cellulose, serves as an external skeleton that protects and supports the animal's body.123