Phylum Echinodermata
“Spiny skin”
Echinoderms are a
“noble group especially
designed to puzzle the
Zoologist.”
Libbie Hyman,
American Zoologist
“Tis strange – but true:
For truth is always strange;
Stranger than fiction.”
- Lord Byron (Poet)
A. Phylum Characteristics
A. Body –Not metameric, adult with pentamerous
radial symmetry
B. Head – No head or brain with few sensory organs
C. Nervous System – Circumoral ring with radial nerves
D. Endoskeleton – Calcium based spines covered by
ciliated epithelium (in most), and pedicellariae
(in some).
- Regenerative abilities.
A. Phylum Characteristics cont.
E. Water-vascular system – Extends from the body surface
with tactical like projections
F. Locomotion – Tube feet, movement of spines, or by
movement of the arms
G. Digestive system – Usually complete
-Sea cucumbers & sea-urchins- consume food with mouth
- Sea stars- Most efficient!!!!
H. Respiration – Papulae or tube feet
A. Phylum Characteristics cont.
I. Excretory – Most have complete digestive systems, some
do have incomplete.
- Lack specialized excretory organs
J. Sex – Separate with fertilization usually external
K. Embryology – Development through free-living bilateral
larval stages with a metamorphosis to a radial
adult form.
B. Ecological relationships
a. Habitats
i. Without the ability to osmoregulate they are not
found in brackish or fresh water
ii. They inhabit all oceans at all depths
iii. Mostly benthic
B. Ecological relationships cont.
-Feeding
i. Some are particle feeders (mostly Sea lilies and
Sea feathers)
ii. Some are predatory (mostly Sea stars)
iii. Some are scavengers (mostly brittle stars)
iv. Some are browsers (Sea Urchins)
C. Economic Relationship
a) Some species are commercially harvested and eaten
b) May have detrimental affects on commercial clam and
oyster beds
Phylum Echinodermata Class Comparisons
Phylum Echinodermata Class Comparisons
A.Class Asteroidiea: Sea Stars
1.
2.
3.
4.
Typically 5 arms
Tube feet important in feeding & gas exchange
Simple reproductive system
Life Cycle Free swimming larva → to Attached, sessile
Juveniles → to Free moving adults.
B. Class Ophiuroidea: Brittle Stars
1.
2.
3.
4.
5.
Bursae- used for gas exchange & reproduction
No pedicellariae or ampullae
Ambulacral grooves are closed
Madreporite is on ventral surface
Move by using their arms & are the most rapid of the
echinoderms
C.Class Enchinoidea: Sea Urchins, Sand dollars, &
Heart Urchins
1. Dermal ossicles are closely fitting plates
2. No Arms
3. Sand dollars & Heart urchins have evolved back to
bilateral symmetry
Callum Hall
D. Class Holothuroidea: Sea Cucumbers
1. Greatly elongated through the ventral-dorsal surface
(lay on their side)
2. Some return to bilateral symmetry
3. Small dermal ossicles and a soft body
E. Class Crinoidea:
Sea Lilies & Feather Stars
1. Lie with oral side up
2. Attached to substratum by a stem