PHYLUM ECHINODERMATAmeans spiny skin

1
PHYLUM ECHINODERMATA (means spiny skin)
ex seastars, sea urchins, sand dollars
Why are they considered advanced?
1. endoskeleton of calcium carbonate plates
2. bilaterally symmetrical larvae
3. water vascular system instead of muscles is a
big advantage in predatory situations
4. highly regenerative - can eviscerate
5. separate sexes external fertilization
2
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. Adults have pentamerous (5) radial symmetry
.
4. Respiration is by diffusion through the skin.
3
Seastars are scavengers and eat a variety of
organisms.
The seastar can open a clam shell a few
centimeters wide.
Then by inverting its stomach into the shell,
the clam is digested and absorbed.
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!