(larvacean)

(solitary sea squirts)

Phylum CHORDATA (tree from Tree of Life; traits from Brusca & Brusca 1990 p.873. Nielson 1995 and Ruppert et al. 2004 p. 957; 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)

Back to Zool 250 tree for animal phyla or Deuterostomia.

TRAITS SUPPORTING EACH CLADE (** plesiomorphic- a primitive state, not unique to clade):

C= CHORDATA (living classes): a) pharynx with ciliated U-shaped gill slits** b) endostyle (thyroid gland in vertebrates) c) notochord d) dorsal hollow nerve cord e) dorsal, somatic post-anal tail** f) segmented myomeres g) protocoelic nephridium (=axial complex) lost h) 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) reversible direction to heart beat g) nephridia & coelom absent h) hermaphroditic i) primitive sperm morphology j) dstrict cell fate determination k) multiciliated cells

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 c) muscular notochord extends into rostrum 5= VERTEBRATA= Craniata: a) thyroid gland (derived from endostyle) b) full endoskeleton with cranium c) anterior end of neural tube enlarged as brain d) multilayered (stratified) epithelium e) blood vessels lined with endothelium f) glomerular kidney g) polar bodies from oral pole h) multiciliated cells