BILATERIAN ANIMALS (modified from WWW Tree of Life; traits & tree after Ruppert & Barnes 1994 p. 1052 and Brusca & Brusca 1990 p.873).

                ==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==|       =========== Echinodermata (starfish, urchins, sea cucumbers,etc.)
              |   =5==|
              =4==|   ===6======= Hemichordata (acorn worms, pterobranchs))
                  |
                  ============================================== TO CHORDATA ===>

TRAITS SUPPORTING EACH CLADE (** plesiomorphic- a primitive state, not unique to clade): 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 ----> tripartite body plan protocoel=axocoel ----> protosome mesocoel=hydrocoel ----> mesosome metacoel=somatocoel ----> metasome e) monociliated cells** 1: a) paired, lateral fins b) grasping spines around mouth c) ventral ganglion 2: a) no compelling synapomorphies 3 (Lophophorates): a) mesocoelic tentacles form a lophophore b) reduction in prosome c) U-shaped gut

4: a) protocoelic nephridium (=axial complex) b) protocoel has external coelomopore c) tri-coelomate organization of larval stage** d) ciliated pharyngeal pores/gill slits e) post-anal tail f) stiffened, notochord-like structure g) gonads with separate gonoducts 5: a) protocoelic nephridium/axial complex b) protocoel has external coelomopore c) arval similarities (echinoderm auricularia & bipinnaria resemble enteropneust tornaria larvae) 6 (Hemichordata): a) stomochord (homologous with notochord?) b) mucocciliary pre-oral locomotory organ c) paired valved collar ducts d) ventral post-anal tail

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

                             ======= Cl. Larvacea (the appendicularians)
      ==1== UROCHORDATA =====|
      |                      |   === Cl. Thaliacea (salps, doliolids, pyrosomes)
      |                      ==2=|
      |                          === Cl. Ascidiacea (sea squirts)
<<=C==|
      |   ==4======================= CEPHALOCHORDATA (lancelets)
      =3==|
          |                   ====== Myxini (hagfish)
          ==5== VERTEBRATA ===|
                              ====== other vertebrates (fish, amphibians, reptiles, birds, mammals)

TRAITS SUPPORTING EACH CLADE (** plesiomorphic- a primitive state, not unique to clade): C= CHORDATA (living classes): a) segmented myomeres b) cephalization c) notochord d) dorsal, somatic post-anal tail** e) dorsal hollow nerve cord f) pharynx with ciliated U-shaped gill slits** g) endostyle (thyroid gland in vertebrates) h) protocoelic nephridium (=axial complex) lost i) metacoel lost (i.e., coelom not tripartite) 1 (SubPh. Urochordata): a) tadpole shaped body as adult (Larvacea) or larva (Ascidiacea) b) outer acellular tunic or temporary house c) 2 (Larvacea) or 1 (Ascidiacea) exhalent siphons or spiracles from pharynx d) U-shaped gut e) gill-slits no longer U-shaped f) primitive sperm morphology g) dstrict cell fate determination

2: a) derived sperm morphology 3: a) segmentally arranged muscles b) differentiation of neural tube c) ciliated, U-shaped gill slits** 4 (SubPh. Cephalochordata): a) buccal complex (wheel organ, vestibule, oral hood, buccal cirri) b) unusual protonephridia-like nephridia 5 (SubPh. Vertebrata= Craniata): a) thyroid gland (derived from endostyle) b) full endoskeleton with cranium c) anterior end of neural tube enlarged as brain d) polar bodies from oral pole

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