(larvacean)

(solitary sea squirts)

Phylum CHORDATA (tree from Tree of Life; traits from Delsuc et al. 2006 Brusca et al. 2016 p. 1041, Nielson 2012 p. 349, and Ruppert et al. 2004 p. 957; taxa in FULL UPPER CASE indicate the three chordate subphyla)

(lancelet)

      ===========1======================= CEPHALOCHORDATA (lancelets)
      |
      |                            ====== Cl. Larvacea (appendicularians)
      |   ===3= UROCHORDATA =======|
      |   |       (=Tunicata)      |  === Cl. Thaliacea (salps, doliolids, pyrosomes)
<<=C==|   |                        =4=|
      |   |                           === Cl. Ascidiacea (sea squirts)
      =2==|
          |                        ====== Cyclostomata (jawless hagfish & lampreys)
          ======5= VERTEBRATA =====|
                    (=Craniata)    ====== Gnathostomata (jawed vertebrates)

Back to Zool 250 tree for animal phyla or Deuterostomia.

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

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= CEPHALOCHORDATA: a) buccal complex (wheel organ, vestibule, oral hood, buccal cirri) b) unusual protonephridia-like nephridia c) muscular notochord extends into rostrum 2: a) multiciliate epithelia b) loss of 6 HOX genes

3= UROCHORDATA: (= TUNICATA) a) tadpole shaped body as adult (Larvacea) or larva (Ascidiacea) b) outer acellular (cellulose) cuticle 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) strict cell fate determination k) destruction of HOX gene cluster & loss of Hox7 & Hox8 (David & Mooi Evo Devo 2014 5:22) 4: a) derived sperm morphology 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