1. Phylum Echinodermata
The Echinoderms: Sea Stars, Brittle Stars, Sand Dollars, Sea Urchins, Sea Cucumbers, Feather Stars, & Sea Daisies

2. Echinodermata = Spiny Skin
Characteristics of Echinoderms
ALL forms are marine.
Endoskeleton in the form of calcium carbonate plates called ossicles.
Adults have radial symmetry (body parts are in multiples of 5); Larval forms have bilateral symmetry.
Radial symmetry allows the organism to have 360° of sensory, feeding, and locomotion.
Have water-filled canals (water-vascular system) that end in tube-feet, used for locomotion, feeding, excretion, & respiration (the last two are accomplished by diffusion.)
Complete digestive system, meaning that they have an anus.
Nervous system consisting of a nerve net, nerve ring, and radial nerves.
Echinodermata = Spiny Skin

3. Water-vascular System of a Starfish
Includes a ring canal that surrounds the mouth; ring canal usually opens to the outside or to the body cavity through the madreporite and stone canal.
5 (or a multiple of 5) radial canals branch from the ring canal to allow for the flow of water through the animal.
Many lateral canals branch from the radial canals and end at the tube-feet.
Water-vascular System of a Starfish

4. Aboral Surface
Madreporite

5. Water-vascular System video
External Ventral View
Internal View
Water-vascular System video

6. Water-vascular System

7. Tube-feet are topped by a bulblike, muscular ampulla and end in a suction cup-like podia.
When the ampulla contracts, it forces water into the tube-foot, which then extends; when the podia attach to a substrate (either food or the bottom of the ocean) it forms a vacuum, just like the suction cups you’re familiar with, but way more intense!!
Some tube-feet at the ends of the arms have even become modified to detect light and serve as eyespots!
Tube-feet

8. Tube feet

9. Fig. 22.3a

10. Some species feed on animal remains on the ocean floor.
Some filter plankton through their mouth pore.
Some scrape food off rocks.
Others are predacious, seeking other invertebrates (molluscs, arthropods, etc.) for food.
What Do They Eat? video

11. Class Asteroidea: The Sea Stars video
Well known for their powers of regeneration. They can regenerate any part of a broken arm! If the broken arm contains a portion of the central disk, an entire starfish can be regenerated! However, this is a slow process that usually takes about a year.
Sea Stars are dioecious, and reproduce sexually through external fertilization.
Class Asteroidea: The Sea Stars video

12. Class Ophiuroidea: The Brittle Stars
Often small in size, (1 to 3 cm) they tend to occupy crevices in rocks and coral.
Brittle star tube-feet lack ampullae and suction-cupped podia.
Brittle stars can regenerate and have even developed a defense mechanism called autotomy where they can voluntarily drop an arm as an escape reaction and then grow it back later.
These guys are dioecious and reproduce sexually.
Class Ophiuroidea: The Brittle Stars

13. Class Echinoidea: The Sea Urchins & Sand Dollars
These guys have a chewing mouthpart, similar to a mollusc’s radula, called Aristotle’s lantern. It consists of about 35 ossicles and attached muscles used to cut and shear food.
Dioecious, sexual reproduction.
Class Echinoidea: The Sea Urchins & Sand Dollars

14. Class Holothuroidea: The Sea Cucumbers
Sea cukes have a cool defense mechanism called evisceration. They can excrete not only a sticky mucus, but also their entire digestive tract and respiratory organs through their anus when threatened.
Can regenerate lost parts.
Dioecious, with external sexual fertilization
Class Holothuroidea: The Sea Cucumbers

15. Class Crinoidea: The Feather Stars
These are swimming and crawling animals.
Can regenerate.
Dioecious with external sexual reproduction.
Class Crinoidea: The Feather Stars

16. Class Concentricycloidea: The Sea Daisies
Usually less than 1cm. in diameter.
Have no digestive system.
No larval stage.
Class Concentricycloidea: The Sea Daisies