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Why do adult sea squirts lose their tails and notochords?

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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.

Adult sea squirts, which are members of the subphylum Tunicata, lose their tails, notochords, and nerve cords during metamorphosis because these structures are specialized for the larval stage.12

The tunicate tadpole larva is free-swimming and non-feeding, relying on its muscular tail, notochord, and nerve cord to navigate and locate a suitable substrate for attachment. Once the larva attaches to a surface, it transitions into a sessile adult form. During this process, the larval features are resorbed, and the tail tissue is broken down to provide essential food reserves for the developing animal. This regression allows the organism to shift its energy toward the growth and structural changes required for its sedentary, filter-feeding adult life.1324