Appendicularia

Appendicularia, also called Larvacea and known informally as larvaceans or copelates, is a class of solitary, free swimming tunicates found throughout oceans worldwide. Unlike most other tunicates, larvaceans keep their tadpole like shape and notochord as adults rather than losing it after a larval stage. They are transparent planktonic animals typically two to eight millimeters long including the tail, living in the sunlit upper waters of the open ocean, though a few giant larvaceans can reach ten centimeters.