Phylum Echinodermata
(Means spiny skin)
Echinodermata
Classes
Asteriodea(Stelleroids)
Sea stars
Aka starfish
Echinodermata
Classes
Crinoidea/Crinoids
Feather stars
Sea lilies
Echinodermata
Classes
Echinoidea/Echinoids
Sea urchins, sand dollars
Compact body within a
shell
No arms, often spiny
Echinodermata
Classes
Holothuroidea
(Holothuriods)
Sea cucumbers
Elongated body
Leathery body wall with
embedded ossicles
(bony plates)
Ophiunoidea (Add this to your hand out!)
Brittle stars, Basket stars
Echinodermata
Common Characteristics
Radial Symmetry
as opposed to bilateral
Like spokes on a wheel
Echinodermata
Common Characteristics
Body may be round
Or Cylindrical
Or star shaped
With 5 or more
ambulacra (radiating
areas)
Echinodermata
Common Characteristics
Endoskeleton
with spines or spicules
Can regenerate lost
parts
Echinodermata
Common Characteristics
No head or brain
Few specialized sensory
organs
Simple Nervous system
Nerve ring / radial
nerves
No excretory organs
Echinodermata
Common Characteristics
Water Vascular System
Water is taken in at the
madreporite
Helps with respiration,
Circulation and movement
Specialized structures…
•Mouth and anus – ingestion and excretion of digestive
wastes
•Madreporite – sieve like structure through which water is
taken in.
• Some species - gills
• Tube feet for movement
•Gonads - make gametes (sperm and eggs)
Echinodermata
Anatomy
Echinodermata
Reproduction
May be hermaphrodites
Or gonochoric
(two distinct sexes)
Usually release sperm /
egg into the water column
External fertilization
Many species synchronize
this, along the lunar
cycle
Echinodermata
Nutrition
Most sea urchins scrape
algae off surfaces
They have specialized
mouthparts for this
Called Aristotle’s lantern
A few are scavengers or
predators
Echinodermata
Nutrition
Brittle stars are mostly
scavengers
They crawl about on the
bottom looking for dead
stuff
Some are active filter
feeders
Or just lay about waiting
for food to float by and
stick to them
Echinodermata
Nutrition
Sea stars are carnivores
They tear open mollusks
with their arms
Then extrude their own
stomach out of their
mouths to release
digestive juices into the
clam’s body.
Answer to #6 on the hand out
They eat mollusks like clams and
mussels, some eat coral (‘Crown of
thorns’)