BILATERIAN ANIMALS (modified from WWW Tree of Life, after Ruppert & Barnes 1994 p. 1053)

                ==C========= coelomate protostomes (arthropods, annelids, molluscs, etc.)
          ======|
     ==P==|     ================= Platyhelminthes (flatworms, tapeworms, etc.)
     |    |
     |    =(placement uncertain)= pseudocoelomates (nematodes, rotifers, etc.)
<<===|
     |    =1===================== Chaetognatha (arrow worms)
     |    |
     ==D==|   =3================= LOPHOPHORATES (Ph. Bryozoa, Brachiopoda, etc.)
          |   |
          =2==|   =5============= Echinodermata (starfish, urchins, sea cucumbers,etc.)
              |   |
              =4==|   ==7======== HEMICHORDATA (acorn worms, pterobranchs)
                  =6==|
                      =========================================== TO CHORDATA ===>

P= PROTOSTOMIA: a) spiral, determinate cleavage, b) mesoderm from mesenchyme cells, c) mouth (and sometimes anus) from blastopore, d) multiciliated cells, e) trochophore-like larva
C= COELOMATE PROTOSTOMES: a) coelom via schizocoely
D= DEUTEROSTOMIA: a) radial, indeterminate cleavage**, b) coelom via enterocoely, c) blastopore yields anus, d) tripartite coelom (protocoel=axocoel, mesocoel=hydrocoel, metacoel=somatocoel) associated with tripartite body plan (protosome, mesosome, metasome), e) monociliated cells**
1: a) paired, lateral fins, b) grasping spines around mouth, c) ventral ganglion
2: a) mesocoelic tentacles
3: a) mesocoelic tentacles form a lophophore**, b) reduction in prosome, c) U-shaped gut
4: a) protocoelic nephridium (=axial complex), b) coelomopore connecting protocoel to outside of body
5: a) pentaradial symmetry, b) endoskeleton of calcareous ossicles with unique perforated structure, c) unique water vascular system with suckerless podia, d) open ambulacral grooves, e) mouth & anus on oral surface, f) attached to substratum with aboral surface, g) tripartite coelom in larva (axocoel, hydrocoel, somatocoel)**, h) mesocoelic tentacles lost
6: a) ciliated (U-shaped?) gill slits
7: a) stomochord (homologous with notochord?), b) ciliated (U-shaped?) gill slits (Cl. Enteropneusta), c) mesocoelic tentacles form a lophophore (Cl. Pterobranchia)**

Phylum CHORDATA (tree from WWW Tree of Life; traits from Brusca & Brusca 1990 p.873)

      =1================== Urochordata (tunicates: sea squirts, larvaceans, salps, etc)
<<=C==|
      |   =3============== Cephalochordata (lancelets)
      =2==|
          |            === Myxini (hagfish)
          =4==Craniata=|
                       === Vertebrata (fish, amphibians, reptiles, birds, mammals)

C= CHORDATA : (living classes): a) segmentation, b) cephalization, c) notochord, d) somatic post-anal tail, e) dorsal hollow nerve chord, f) ciliated, U-shaped gill slits**, g) endostyle, h) protocoelic nephridium (=axial complex) lost, i) mesocoel & mesocoelic tentacles lost, j) metacoel lost
1: a) outer acellular tunic, b) inhalent & exhalent siphons
2: a) segmentally arranged muscles, b) differentiation of neural tube, c) ciliated, U-shaped gill slits**
3: a) buccal complex (wheel organ, vestibule, oral hood, buccal cirri), b) protonephridia
4: a) thyroid gland (derived from endostyle), b) full endoskeleton with cranium, c) anterior end of neural tube enlarged as brain

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