Zoology 250 Phylogenetic Trees (2017)


(modified from Tree of Life after
Ruppert et al. 2004 p. 220, 868 and
Brusca & Brusca 2003 p. 875)

(asteroid echinoderm)

(enteropneust hemichordate)

     ============================ Protostomia
<<===|    ?(branch uncertain)=1== Chaetognatha$ (arrow worms)
     |    |
     |    ?(branch uncertain)=2== lophophorates$ (Ph. BRYOZOA, BRACHIOPODA, etc.)
          |          ==5========= XENOTURBELLIDA (Xenoturbella)
          |          |
          |      =4==|    ======= ECHINODERMATA (starfish, urchins, sea cucumbers,etc.)
          |      |   ==6==|
          ===3===|        ==7==== HEMICHORDATA (acorn worms, pterobranchs)
                 ================ CHORDATA

Back to Zool 250 tree for animal phyla.

TRAITS SUPPORTING EACH CLADE (** plesiomorphic- a primitive state, not unique to clade) AND HIGHER TAXA:
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**
a) paired, lateral fins
b) grasping spines around mouth
c) ventral ganglion
d) postanal testes
a) mesocoelic tentacles form a lophophore
b) mesosome secretes covering (tube, shell, cuticle)
c) reduction in prosome
d) U-shaped gut
a) protocoelic nephridium (=axial complex)
b) tri-coelomate organization of larval stage**
c) pharynx with ciliated pores/gill slits
d) post-anal tail
e) stiffened, notochord-like structure
f) gonads with separate gonoducts
a) SALMFamide-2 short neuropeptide *
b) mitochondrial gene order *
a) mid-ventral mouth, no anus *
b) brain, ganglia, nerve cords lacking *
c) diffuse, intraepidermal nervous system *
d) loss of: gill slits, post-anal tail, coelomic cavities, distinct gonad *
a) protocoel has external coelomopore
b) larval similarities (echinoderm auricularia & bipinnaria resemble enteropneust tornaria larvae)
d) michondrial gene order *
e) unique mitochondrial triplet AUA codes for Isoleucine, not Methionine as in other Bilateria *
a) stomochord (homologous with notochord?)
b) muco-ciliary pre-oral locomotory organ
c) paired valved collar ducts
d) ventral post-anal tail
e) dorsal and ventral longitudinal nerve cords
f) multiciliated cells (Enteropneusta only)

* characters from Telford 2008

$ Increasing evidence - both molecular and morphological - suggests the Chaetognatha and the 'lophophorate' phyla belong within the Protostomia rather than the Deuterostomia. Their placement within the Protostomia, however, remains much debated. They are placed in the Deuterostomia here to reflect the traditional view that, although they possess traits of both protostomes and deuterostomes, the morphological and developmental traits shared with deuterostomes outnumber those shared with protostomes.

Return to Zool 250 Home Page or try your skill at the Invertebrate Diversity Quiz.

Copyright (c) 2017 by A. Richard Palmer. All rights reserved.
(revised Dec. 19, 2016)