The anus empties into the excurrent siphon. When disturbed, tunicates eject a jet of water through the excurrent siphon, so they are commonly called sea squirts. Adult tunicates bear little resemblance to other chordates. They lack a notochord, a nerve cord and tail. They possess only pharyngeal slits.
Larval tunicates are free swimmers and possess all four chordate characteristics.
Larva attach by the head on a surface and undergo metamorphosis to adult form. Subphylum Cephalochordata Animals in the subphylum Cephalochordata are known as lancelets due to their bladelike shape. Chordate characteristics are prominent and persist in the adult. Postanal tail Cephalochordates are marine filter feeders. They burrow tail first into the sand with only the anterior exposed.