Zoology 250 Phylogenetic Trees (2017)

(feather star)


(traits and tree after Brusca et al. 2016 1002;
additional traits from Ruppert et al. 2004 p. 926)

(sea urchin)

(brittle star)

(sea cucumber)

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

     $ some consider the Ophiuroidea to be the sister group of the Echinozoa based on the ambulacra

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:

E= ECHINODERMATA (living classes):
a) pentaradial symmetry
b) endoskeleton of calcareous ossicles with unique perforated structure (stereom)
c) unique water vascular system with suckerless podia
d) open ambulacral grooves
e) mouth & anus on oral surface**
f) sessile; attached to substratum with aboral surface (primitively)
g) multiple gonads** #
h) spherical sperm** #
i) gill pores/slits absent in adults
j) mutable collagen tissue
k) monociliated cells**
l) dipleurula larvae**
m) tri-partite coelom in late larval stage**
1= Crinoidea:
a) sessile; attached to substratum with stalk (primitively)**
b) multiple arms bearing open ciliated grooves for suspension feeding
c) podia lack suckers**, not used for locomotion
d) ring canal has many stone canals
e) use articulated cirri for locomotion (derived forms)
f) vitellaria larvae
a) free living (not sessile) #
b) oral surface becomes ventral
c) anus becomes dorsal
d) use podia (tube feet) for locomotion
e) stone canal becomes ossified #
f) polian vesicles (or similar) on ring canal
a) body plan of five arms connected to an oral disc
4= Asteroidea:
a) thick arms, broadly connected to oral disc
b) eyespot at each arm tip
c) podia possess suckers
d) pedicellaria (2 orders)
e) paired pyloric cecae in each arm
f) gonads in arms
g) bipinnaria & brachilaria larvae
5= Ophiuroidea:
a) snake-like arms narrowly connected to oral disc
b) arm ossicles like miniature 'vertebrae'
c) oral madreporite
d) anus absent in adult
e) ophiopleuteus larvae
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
e) podia possess calcified disc #
f) podia possess secretory goblet & tuft cells #
g) esophagous has internal skeleton #
h) well developed hemal system
7= Echinoidea:
a) fusion of skeletal ossicles to form globular or discoidal test
b) test covered with articulated, moveable spines; spines quite large in some taxa
c) pedicellaria (all orders)
d) Aristotle's lantern
e) secondary bilateral symmetry (some groups)
f) Polian vesicles lost (replaced by Tideman's bodies)
g) elongate sperm 
h) echinopleuteus larvae
8= Holothuroidea:
a) ossicles greatly reduced & isolated in thick dermis
b) fleshy body
c) elongation of body along oral-aboral axis
d) oral podia modified as particle feeding tentacles
e) secondary bilateral symmetry (some groups)
f) paired, internal respiratory trees
g) single gonad #
h) auricularia larvae

# traits from Janies 2001

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)