Phylum Echinodermata
I.
General Characteristics
A.
Symmetry – Mostly Radial Sometimes Bilateral
B.
Body has more than two cell layers, tissues and organs.
C.
Eucoelomate
D.
Deuterostome
E.
Body shape varies
F.
No head
G.
Endoskeleton
H.
Few Sense Organs
I.
Nervous system - a circum-oesophageal ring.
J.
Open circulatory system.
K.
Has water vascular system, which hydraulically operates the tube feet or feeding tentacles.
L.
Without excretory organs.
M.
Normally possesses a epidermal system of calcareous plates
N.
Reproduction –sexual; separate sexes; external fertilization
O.
Habitat - Marine Environments.
II.
Classes of Echinodermata
A.
Class Asteroidea
1. Have 5 arms usually
2. Mouth located in center of oral surface pointing downward
3. Has a Water Vascular System
a. Opening of the water vascular system the madreporite (=sieve plate)
b. Water enters the Madreporite and goes through the stone canal to the ring canal
c. Water then passes through a radial canal extending into each arm
d. All along the length of these canals are lateral canals that terminate in a bulb-like structures called ampullae equipped with tube feet
e. Tube feet line the grooves on the oral surface- ambulacral grooves
4. Has Mouth and Stomach
5. Has short intestine – extends from stomach to anus.

6. Endoskelton made up of calcareous plates that penetrate the dermis as spines
7. Between the spines and plates are projections called papulae, which function in gas exchange and excretion
8. Other projections on the body wall include tiny jaw-like appendages called pedicellaria
9. Photoreceptors – respond to light
10. Examples: Starfish, Brittle stars
B. Class Ophiuroidea
1. Characteristics similar to class Asteroidea
2. Main difference between starfish and brittle stars is brittle stars have much thinner arms.
3. Examples: Brittle stars
C. Class Echinoidea
1. No arms arms
2. Body is enclosed in a shell or test
3. Body surface is usually covered with moveable spines
4. Spherical body
5. Ambulacral plates bearing tube feet that radiate out toward the aboral surface
6. Use podia and spines during locomotion
7. The spines are moveable and articulate with the with the calcareous ossicles
8. Examples: Sea Urchins, Sand Dollars
9. Feeding – Scrap algae off of rocks then using a chewing apparatus called
Aristotle's Lantern
D. Class Holothuroidea
1. No arms
2. Endoskeleton is reduced to a few Ossicles on the surface
3. Fairly soft-bodied
4. Locomotion – using false feet and by muscular contractions
5. Examples: Sea Cucumber
6. Oral end of the body has a group of tentacles surrounding the mouth; used
in feeding
7. Have a muscular cloaca that is partly used in gas exchange
8. Gas exchange structures are branching structures called respiratory trees
E. Class Crinoidea
1. Most primitive of echinoderms
2. Oral surface is upward
3. Has a stalk
4. Body portion attached to the stalk is the crown;
5. Has branches called pinnules
6. Ciliated around the mouth