File:Comparison of Three Invertebrate Chordates.svg

English: A. Lancelet, B. Larval tunicate, C. Adult tunicate. 1. Notochord, 2. Nerve chord, 3. Buccal cirri, 4. Pharynx, 5. Gill slit, 6. Gonad, 7. Gut, 8. V-shaped muscles, 9. Anus, 10. Inhalant syphon, 11. Oral/Inhalant siphon, 12. Exhalant siphon, 13. Heart, 14. Stomach, 15. Esophagus, 16. Intestines, 17. Atrium, 21. Tunic.

English: A. The lancelet is a small worm-like animal with a head end, complete with a mouth and simple feeding structures; a tail end with an anus and post-anal tail fin; a simple digestive tract; a pharynx with gill slits; a dorsal stiffened rod (notochord); V-shaped muscles; and a dorsal nerve chord—all of which are synapomorphies with chordates. B. & C. Tunicates normally live in shallow seas partially buried in the sand. Tunicates have jelly sacks with two siphons, which are tubular openings, located on the top of the organism. Water is sucked in through the inhalant siphon and enters the pharynx. It passes through the gill slits in the wall of the pharynx the food particles are separated and are passed into the gut. The water is excreted from the exhalant siphon. Sea squirts are most commonly found clinging to the side of rock pools on the beach. Tunicates have free swimming larvae which are similar to the lancelet.