(larvacean)

(solitary sea squirts)

Phylum CHORDATA (tree from WWW Tree of Life; traits from Brusca & Brusca 1990 p.873; taxa in FULL UPPER CASE indicate the three chordate subphyla)

(lancelet)

                             ======= 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 (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 (Cephalochordata): a) buccal complex (wheel organ, vestibule, oral hood, buccal cirri) b) unusual protonephridia-like nephridia 5 (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