Chordate
Classification
All chordates are deuterostomes. This means that, during the embryo development stage, the anus forms before the mouth. All chordates are based on a bilateral body plan. All chordates are coelomates, and have a fluid-filled body cavity called a coelom with a complete lining called peritoneum derived from mesoderm (see Brusca and Brusca). 1 = bulge in spinal cord ("brain") 2 = notochord 3 = dorsal nerve cord 4 = post-anal tail 5 = anus 6 = digestive canal 7 = circulatory system 8 = atriopore 9 = space above pharynx 10 = pharyngeal slit (gill) 11 = pharynx 12 = vestibule 13 = oral cirri 14 = mouth opening 15 = gonads (ovary / testicle) 16 = light sensor 17 = nerves 18 = metapleural fold 19 = hepatic caecum (liver-like sack) The following schema is from the fourth edition of Vertebrate Palaeontology. The invertebrate chordate classes are from Fishes of the World. While it is structured so as to reflect evolutionary relationships (similar to a cladogram), it also retains the traditional ranks used in Linnaean taxonomy.
Chordate-6