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)

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**, not used for locomotion
2: a) oral surface becomes ventral, b) anus becomes dorsal, c) podia possess suckers, d) use podia (tube feet) for locomotion
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) arms absent, b) ambulacral grooves extend from oral to aboral pole, c) aboral surface restricted to small region around anus, d) 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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