1. Echinoderms

2. Diversity Echinodermata means “spiny skin”
Echinoderms usually inhabit shallow coastal waters and ocean trenches
organisms in this class include:
Sea stars
Brittle stars
Sand dollars
Sea cucumbers

3. Characteristics
change from a free-swimming bilaterally symmetrical larva to a bottom-dwelling adult with radial symmetry.
Most have five radial appendages or multiples which is known as pentaradial symmetry
they have an endoskeleton that is made up of calcium plates, may include protruding spines

4. Have small feet called tube feet that aid in movement, feeding, respiration, & excretion.
Do not have circulatory, respiratory or excretory systems.
Have a nervous system but no head or brain.
There are two sexes and they can produce sexually and asexually.

5. Evolution & Classification
Echinoderms are from the Cambrian period & date back to over 500 million years ago
scientist believe that they evolved from bilaterally symmetrical ancestor.
The inferred ancestral larva is very similar to the modern Sea star larva.

6. Structure & Function

7. Body Symmetry evolved from animals with bilateral symmetry
adult echinoderms possess radial symmetry
All echinoderms exhibit fivefold radial symmetry in portions of their body at some stage of life (5 parts around central axis), even if they have secondary bilateral symmetry
LARVAE ~ bilateral
ADULTS ~ radial

8. Body Plan of the Sea Star
oral surface: mouth located on the underside of the body
aboral surface: top of the body
ossicles: sharp protective spines made of calcium plates, covered with thin epidermal layer
pedicellariae: tiny forceps that protect and clean the body surface

9. Water-Vascular System
Used in locomotion, food capture, & respiration
Network of canals – run throughout body ending w/tube feet
Varying internal water pressure can extend or contract tube feet
Tube feet end in small suction cups

10. Water Vascular System
Water enters madreporite on aboral surface into a short, straight stone canal
Stone canal connects to circular canal around the mouth = ring canal.
Enters five radial canals extending down each arm

11. Water Vascular System
Radial canals carry water to hundreds of paired tube feet.
Bulb-like sacs or ampulla on tube feet contract & create suction

12. Other Body Systems No circulatory, excretory, or respiratory systems
No head or brain
Eyespots on the tips of each arm detect light

14. Reproduction Separate sexes External fertilization
Females produce 200,000,000 eggs / season;

16. Surfaces Mouth on oral surface (bottom / ventral)
Anus on aboral surface (top / dorsal)

17. Feeding & Digestion uses feet
eat mollusks, worms, and slow-moving animals
enzymes help digest food

18. Other Body Parts
fluid in coelom surrounds the organs & distributes nutrients & oxygen
skin gills: protect coelom lining; gases are exchanged
nerve ring: surrounds mouth & branches off into nerve cords in each arm.
Eyespots: on each arm that responds to light
tentacles: responds to touch

19. Reproduction each arm produces sperm & egg occurs externally
bipinnaria: free-swimming larva that develops from fertilized eggs
settles in the bottom and develops into an adult through metamorphosis
reproduce asexually by regenerating lost parts

20. Taxonomists have divided 6,000 species of echinoderms into five classes:

21. Classes of echinoderms
Crinoidea
Asteroidea
Ophiuroidea
Echinoidea
Holothuroidea

22. Crinoidea (“lilylike”)
They include:
Sea lilies
Feather stars
Crinoidea are sessile
they have long stalks that attach to rocks or to the ocean floor
feather stars eventually detach themselves
Sticky tube feet that are at the end of each arm catch food and serve as a respiratory surface.

23. Asteroidea (“star-like”)
starfish or sea stars belong in this class
found all over coastal shores around the world
prey on oysters, clams, and other sea food that is used by people

24. Ophiuroidea (“snakelike”)
largest echinoderm class
includes basket stars & brittle stars
primarily reside under stones & in crevices and holes of coral reefs
have thin brittle arms that break off & regenerate themselves quickly
feed by raking food off the ocean floor with their arms and bottom of tube feet
also trap food with mucous strands between their spines.

25. Echinoidea (“hedgehoglike”)
sand dollars & sea urchins
test: rigid endoskeleton that the internal organs are compacted in
Aristotle’s lantern: complex jaw-like mechanism that is used to grind their food
locomotion: tube feet
protection: barbs on their long spines that are sometimes venomous

26. Sand dollars live along seacoasts & sandy areas
flat, round shape bodies; and adaptation for shallow burrowing
locomotion: short spines (also aid in burrowing & cleaning their bodies)
use tubes to filter food out of water

27. Holothuroidea sea cucumbers belong in this class bodies are soft
how they feed: tentacles around the mouth sweep up sediment from the water
protection: eject internal organs through the anus.
Lost parts are later regenerated.
Process called evisceration

28. Other Unique Features Echinoderms can REGENERATE
ex: sea cucumbers can eject a portion of gut in response to predators and regenerate when safe
Water vascular system (described earlier) is unique to echinoderms

29. Other Unique Features
Crinoids and some brittle stars = passive filter-feeders, absorbing suspended particles from passing water
sea urchins = grazers
sea cucumbers = deposit feeders
starfish = active hunters

30. More Unique Features
Autonomy = The spontaneous self amputation of an appendage when the organism is injured or under attack. The autotomized part is usually regenerated.
“arms” → multiples of 5; some have more because of regeneration