Echinoderms are marine invertebrates with spiny skin and five-part radial symmetry. They include sea stars, brittle stars, sea urchins, sea cucumbers, and sea lilies. Sea stars have arms that are attached to each other and are active predators that eat mollusks and crustaceans. Sea urchins are herbivores that scrape algae and plants using their Aristotle's lantern. Sea cucumbers defend themselves by ejecting toxic internal organs when threatened.

1. Echinoderms
“spiny skin”

2. Echinoderms: Main Characteristics
• Spiny Skin
– Exoskeleton
– Musculoskeletal
• 5 part radial symmetry
– Penta-radial
• Tube feet: Movement
– Water-vascular system
• Benthic organisms

4. Classes
• Asteroidea: Sea Stars
• Ophiuroidea: brittle
stars
• Echinoidea: sea urchins
and sand dollars
• Holothuroidea: Sea
cucumbers
• Crinoidea: Sea Lilies and
feather stars

5. Class Asteroidea: Sea Stars
• Aster = star, oides = in
the form of
• Large Coelome
• Circulatory system:
– use diffusion & cilia to
move gas, nutrients and
waste
• Respiratory system:
– Dermal branchi on skin

6. Diagram the arm of the starfish

7. Asteroidea
• Digestive System:
– Mouth on underside
– Opens into cardiac
stomach
• Folds out of body into prey
to secrete enzymes
– Opens into the pyloric
system
• Nutrients diffuse out of the
pyloric stomach
• Eat:
– mollusks, crustacheans,
polychaetes, coral, detritus

9. The Water Vascular System
• Who can explain how hydraulics work?
• Water Vascular System:
– Made up of a series of water-filled canals that run
down the arms from a canal ring in the center
• Radial canal – ampullae – tubed feet

10. Water Vascular System

11. Asteroidea vs. Ophiuroidea
• Sea Star vs. Brittle Star
• Sea Stars:
– Arms attached to arms
– Carnivores: Active
Predators
• Brittle Star
– Arms NOT attached to
arms
– Not active predators: eat
plankton

12. Echinoidea: Sea Urchins
• Same structure, longer
spines than starfish
– Move by means of tube
feet
• Feeding
– Herbivores, feed on algae
and marine plants
– Grazers
– Scrape food using
ARISTOTLES LANTERN!
• Roles:
– Control algae

13. Sea Cucumbers
• Elongated Body Plan
– Long sea urchin
• Tube feet to move
• Separate sexes
• Take organic nutrients out
of sand
– Use oral tentacles
• Defense:
– release internal organs
– Tubules called cuvierian
tubules: sticky and
poisonous

14. CFU
• What is the etymology of Echinoderm
• What is the organ called that extends and
contracts echinoderm’s tube feet?
• What kind of symmetry are Echinoderms?
• What is a major difference between the feeding
habits of starfish and sea urchins?
• What is the major difference between sea stars
and brittle stars
• Explain how sea cucumbers defend themselves.
Why are they able to do this?