1. Phylum Echinodermata “spiny” “skin”

2. Sea stars
Sea cucumbers
Feather stars
Sand dollars
Sea urchins
Brittle stars

3. Major Classes of Echinoderms
ECHINOIDEA: Includes the sea urchins and sand dollars
ASTEROIDEA: includes the starfish

4. OPHIUROIDEA: includes the brittle stars
(below: a fossilized brittle star)
HOLOTHUROIDEA: includes the sea cucumbers

5. CRINOIDEA: includes the feather stars

6. Characteristics of Echinoderms
Pentaradial symmetry
Have a calcareous skeleton inside their body (endoskeleton)
Complete digestive system
Open/reduced circulatory system (no heart) with a central ring and vessels

7. Simple radial nervous system (no brain)
Reproductive system consists of gonads which take up a significant amount of space in the body cavity
Sexual reproduction with fertilization outside body (most)
Have ciliated, free-swimming larvae
Possess a water vascular system used for gas exchange, feeding and locomotion

8. Taking a closer look at Sea Stars
Possess 5 or more arms which radiate from a central disk
Mouth is located on oral surface (underneath)
Found all over the world (very diverse!)
Most possess a simple light sensitive eye spot at the end of each arm

9. Sea stars Spiny projections on the arms
Tube feet underneath the arms grip objects, move, and gather food
Water vascular system – moves the tube feet

11. The Water Vascular System
A central ring and a series of canals that eventually end in tube feet.
Tube feet are used for movement, feeding and bringing in water for gas exchange.

12. Water vascular system:
Water enters through the madreporite
Ampulla on the top of the tube foot squeezes water into the tube, making it longer
To pull the foot back, the ampulla refills with water, making the foot shorter

14. Tube feet of a sea urchin!
Using muscles to force water into the tube feet extends and pushes them into the ground.
The muscles are then relaxed in order for the tube feet to retract.

15. Digestion Most are predators How to eat a clam (like a sea star):
Pry apart the two shells using your tube feet
Eject your stomach through your mouth into the clam
Digest it inside the shell
Pull your stomach back inside. Mmmmm!

16. Defenses:
Pedicellaria, tulip-like pincers that can inject a painful venom
Incredible powers of regeneration – can regrow all arms if the central disk remains

17. Reproduction – They are Dioecious Animals!
Asexual - split in half
Sexual - mass spawning events

18. Normal Sea Star

19. Mutant Sea Star?

20. Not all sea stars have 5 arms… Sunflower and sun stars have many more.
Mutant?
Not all sea stars have 5 arms…
Sunflower and sun stars have many more.

21. Crown of Thorns Sea Star
Predator of coral polyps
Explosions in crown of thorns populations have devastated some coral reefs

22. Feather, brittle and basket stars
Suspension feeders
Arms transfer plankton from the water to their mouths

23. Basket stars are nocturnal and curl up their arms during the day

24. Basket Star

27. Brittle Star Will voluntarily break off an arm to escape predation
Move quickly (for a sea star)

28. Feather Stars and Sea Lilies

29. Feeding arms on a feather star

30. There may be 5 to 200 arms on a feather star (no tube feet here!).