Tunicates (Sea Squirts and Pyrosomes)

Tunicates, also called Urochordata and commonly known as sea squirts, are chordates whose adult body is essentially a sack with two siphons through which water enters and exits, filtering food inside. Many have a free-swimming tadpole larva that shows every chordate trait, a notochord, dorsal nerve cord, pharyngeal slits and a post-anal tail, before it attaches to a hard surface, loses its tail and mostly dissolves its nervous system. The salps are entirely pelagic tunicates, typically barrel-shaped and sometimes extremely abundant in the open ocean. Tunicates have a sparse fossil record, though some families make microscopic spicules that can be preserved.