チュニック

A sac-like animal with complex organs. May pump seawater for food, or use its interior space to carry out chemical reactions. Can be found in both rooted and free-swimming forms. Free-swimming forms often form tubelike chains, which can reach significant length.

Nerve cord — on this world, the tunicate nerve cord appears to be the ancestor of fish nervous system. Fish may have evolved from free-swimming tunics.

Heterotrophs — they get their food from other organisms, especially plankton and debris suspended in the water.

Tunic — the tunic is a tough, flexible bioplastic which protects the organism while still allowing it to pump water.

Earth analog: tunicates, pyrosomes, sea squirts.