Zoology 250

Clade for ECHINODERMATA


BILATERIAN ANIMALS (modified from WWW Tree of Life, after Ruppert & Barnes 1994 p. 1053)

                ==C========= coelomate protostomes (arthropods, annelids, molluscs, etc.)
          ======|
    ==P===|     ================= Platyhelminthes (flatworms, tapeworms, etc.)
    |     |
    |     =(placement uncertain)= pseudocoelomates (nematodes, rotifers, etc.)
<<==|
    |    ======================== Chaetognatha (arrow worms)
    |    |
    ==D==|  ===================== lophophorates(bryozoans, brachiopods, etc.)
         |  |
         ===|  ============================================ ECHINODERMATA ====>
            |  |
            ===|  =============== Hemichordata (acorn worms, pterobranchs)
               ===|
                  =============== Chordata (sea squirts, vertebrates, etc.)

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
D= DEUTEROSTOMIA: a) radial, indeterminate cleavage**, b) mesoderm from epithelial cells, c) coelom via enterocoely, d) blastopore yields anus, e) tripartite coelom & body plan, f) monociliated cells**
C= COELOMATE PROTOSTOMES: a) coelom via schizocoely



Phylum ECHINODERMATA (tree/traits from Brusca & Brusca'90 p. 834, Ruppert & Barnes 1994)

        ==1================================= Crinoidea (sea lilies, feather stars)
<<=E====|
        |     ==3=========================== Asteroidea ('true' starfish)
        ==2===|
              |     ==5===================== Ophiuroidea (brittle stars)
              ==4===|
                    |     ==7=============== Echinoidea (sea urchins)
                    ==6===|
                          ==8=============== Holothuroidea (sea cucumbers)

Traits supporting each clade (** plesiomorphic- a primitive state, not unique to clade):

E= ECHINODERMATA: (living classes): a) pentaradial symmetry, b) endoskeleton of calcareous ossicles with unique perforated structure, c) unique water vascular system with suckerless podia, d) open ambulacral grooves, e) mouth & anus on oral surface**, f) attached to substratum with aboral surface (primitively)
1: a) multiple arms bearing open ciliated grooves for suspension feeding, b) podia lack suckers**
2: a) oral surface becomes ventral, b) anus becomes dorsal, c) podia possess suckers
3: a) five generally thick arms broadly connected to oral disc, b) open ambulacral grooves**, c) pedicellaria** (2 orders)
4: a) closed ambulacral grooves
5: a) five snake-like arms narrowly connected to oral disc, b) podia lose suckers, c) arm ossicles like miniature 'vertebrae', d) anus lost
6: a) ambulacral grooves extend from oral to aboral pole, b) aboral surface restricted to small region around anus, c) podia possess suckers**
7: a) fusion of skeletal ossicles to form globular or discoidal test, b) pedicellaria** (all orders)
8: a) ossicles reduced & isolated, b) elongation of fleshy body along oral-aboral axis, c) oral podia modified as tentacles

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Copyright © 1998 by A. Richard Palmer. All rights reserved. (revised April 4, 1998)