1. Echinoderms

2. Phylum Echinodermata Echinodermata means “spiny skin”
Echinoderms range in habitat from shallow coastal waters to deep ocean trenches
Vary in size from 1 cm to 1 meter
Organisms in this class include:
Sea stars
Sea Urchins
Sand dollars
Sea cucumbers

3. Characteristics Fossil record dates back 500 million years
Ancestors were sessile, most species later evolved ability to move
Deuterostomes
blastopore develops into anus, mouth is secondary
Makes them more closely related to Chordates

4. Characteristics Radial Symmetry
Similar to cnidarians, have no sign of cephalization
However, they develop from bilaterally symmetrical free swimming larvae (probably a sign of ancestry)
Most have pentaradial symmetry
Body parts extend from center along five spokes
Three other major unique characteristics
Endoskeleton made up of calcium carbonate plates called ossicles
Water-vascular system
Tube feet

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Taxonomists have divided 7,000 species of echinoderms into five classes:
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Crinoidea
Asteroidea
Ophiuroidea
Echinoidea
Holothuroidea
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7. Crinoidea (“lily-like”)
Include:
Sea Lilies: Most closely resemble fossils
sessile as adults
Have long stalks that attach to rocks or the ocean floor
Feather stars: can swim or crawl, but may stay in place for long periods
Five arms extend from body and then branch
Sticky tube feet that are at the end of each arm filter food and serve as a respiratory surface
Mouth faces up

8. Crinoidea

9. Ophiuroidea (“snake-tail”)
Largest echinoderm class (2,000 species)
Basket stars: thin, flexible arms. Branch to form coils that look like tentacles
Brittle stars: thin arms that break of easily and regenerate
Primarily reside under stones & in crevices and holes of coral reefs
Some feed by raking food off the ocean floor with their arms and tube feet
Others trap suspended food with mucous strands between their spines.

10. Ophiuroidea

11. Echinoidea (“spine-like”)
Test: rigid endoskeleton that the internal organs are compacted in
Sea Urchins:
Aristotle’s lantern: complex jaw-like mechanism that are used to grind their food
Include teeth that surround the mouth
protection: barbs on their long spines that are sometimes venomous
Sand Dollars
Found in sandy areas along sea coast
Covered in short spines used for burrowing and locomotion

12. Echinoidea

13. Holothuroidea “water-polyp”
Sea cucumbers
Bodies are soft, armless
Modified tube feet form fringe around mouth
Feeding: tentacles around the mouth sweep up sediment from the water
Protection: some can eject internal organs
Lost parts are later regenerated
Process called evisceration

14. Holothuroidea

15. Asteroidea (“star-like”)
Starfish
found all over coastal shores around the world
prey on oysters, clams, and other sea food that is used by people

16. Structure & Function (Using the Starfish)

17. External Structure
Typically have five arms, but some species have as many as 24
Oral surface: the underside of the body where the mouth is located
Aboral surface: top of the body (opposite the mouth)
Body is covered in short spines that give it rough texture
Pedicellariae: tiny pinchers that surround each spine
Protect and clean the body surface

18. Water-Vascular System
Network of water filled canals connected to tube feet
The path (figure 40-7)
Water enters through madreporite (sieve-like plate on aboral surface
Stone canal (tube pathway)
Ring canal (tube that encircles mouth)
Radial canal (tube that extends down each arm)
Carry water to hundreds of hollow tube feet
Valves prevent water from flowing backwards

20. Water-Vascular System
Upper end of each tube foot expands to form a sac called the ampulla
Muscles contract around the ampulla forcing water into tube feet and back out again
This is how the starfish can extend or shorten the tube feet
Enable locomotion

21. Feeding & Digestion Mouth – esophagus – cardiac stomach
Cardiac stomach can be turned inside out through the mouth
Transfers food to pyloric stomach
Connects to a pair of digestive glands in each arm
Most Sea Stars are carnivorous
Mollusks, worms, slow moving animals

22. Other Body Systems
No circulatory, excretory, or respiratory organ systems
fluid in coelom bathes organs & distributes nutrients & oxygen
skin gills: project through coelom lining; allow gas exchange and waste excretion
nerve ring: surrounds mouth & branches off into nerve cords in each arm
Radial nerve runs from ring down each arm
If nerve is cut, tube feet lose coordination
Eyespots: on end of each arm that responds to light
Tentacles: responds to touch

23. Reproduction Most species have separate sexes
each arm contains a pair of ovaries or testes
Fertilization occurs externally
Bipinnaria: free-swimming larva that a fertilized egg develops into
After ~2 months settles in the bottom and develops into an adult through metamorphosis
Regeneration:
Process is very slow
Use as a defense mechanism
Can be used to reproduce asexually