1. PHYLUM ECHINODERMATA (means spiny skinned)
ex: seastars, sea urchins, sand dollars, sea cucumbers, sea lilies
Seastars
Characteristics:
1. Radial (pentamerous) symmetry
2. Internal skeleton (endoskeleton)
3. Complete digestive system
4. Water vascular system with tube feet (hold or sense)
5. Highly regenerative - can eviscerate
6. Separate sexes; external fertilization

2. PHYLUM ECHINODERMATA (means spiny skin)
ex: seastars, sea urchins, sand dollars, sea cucumbers, sea lilies
Why are they considered advanced?
1. endoskeleton of calcium carbonate plates
2. bilaterally symmetric larvae
3. water vascular system instead of muscles is a big advantage in predatory situations
4. highly regenerative - can regrow lost or damaged body parts
5. separate sexes; external fertilization

3. Why are they considered simple?
1. Light-sensitive eyes located at the end of each ray do not provide vision because there is no brain nor head.
2. They have reduced internal organs - no respiratory, circulatory, excretory. No nervous system.
3. Nerve net (no nervous system) – exhibit complex behavior
4. Adults have pentamerous (5-fold) radial symmetry (associated with sedentary lifestyle)
5. Respiration is by diffusion through the skin.

4. Seastars are predators and eat a variety of organisms.
SEA STARS – ASTEROIDEA
Seastars are predators and eat a variety of organisms.
The seastar can open a clam shell a few millimeters wide.
Then by everting its stomach into the shell, the clam is digested and absorbed.
Seastar Eating a Clam
Missing parts from injuries or evisceration are quickly replaced. Any portion of the central disk will regenerate a new seastar - a fact that oyster fishermen learned too late!

5. BRITTLESTARS - OPHIUROIDEA
Brittle stars have long flexible arms extending from a central disk
Brittle stars eat particulate organic matter
Gray Brittle Stars (Ophiura luetkenii) on the move

6. SEA URCHINS- ECHINOIDEA
Sea urchins use tube feet and spines to move
Sea urchins graze on seaweeds, seagrasses and algae
Mouth has complex system of jaws & muscles – Aristotle’s Lantern

7. SEA CUCUMBERS - HOLOTHUROIDEA Sea cucumbers are deposit feeders
Some secrete toxic substances
Some expel their gut and other internal organs - evisceration
Missing parts from evisceration are quickly replaced

8. FEATHER STARS OR SEA LILIES- CRINOIDEA
Crinoids are suspension feeders
Sea lilies are deep water
Feather stars perch and crawl on hard bottom shallow to deep water
Upside down brittle star

9. SEASTAR DISSECTION
Seastar Dissection Seastar External Anatomy Seastar Anatomy Internal