Echinoderms
Phylum Echindermata
•Share common features with chordates
•Radial Cleavage
•Deuterostomes (Blastopore becomes anus)
•Development of true coeloem
•Usually slow moving or sessile
•Usually are radially symmetrical
•Body parts usually radiate from center (frequently as 5
spokes)
•Possess a thick calcium plate endoskeleton surrounded by a
thin skin layer
•Possess a unique Water Vascular System, which continues
throughout animal and extends into extensions called Tube
Feet.
•Functions for locomotion, feeding, & gas exchange.
•Reproduce sexually or through regeneration.
Class Asteroidea
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Include sea stars
Usually have 5 (or
multiple of 5) arms
radiating from central
disk
Tube feet located
underneath each arm
used for locomotion &
grasping prey. Operate
by hydraulic
principles.
Anatomy of a Sea Star
Feeding

Feed on mollusks
by pulling shells
apart and extending
stomach outside the
mouth into the
bivalve. The bivalve
is digested within
it's shell. The sea
star than re-ingests
its stomach
Reproduction
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Can reproduce
sexually by releasing
sperm and egg.
Can reproduce by
regeneration
Sea Stars
Class Ophiuroidea
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Include Brittle
Stars
Distinct central
disks with long
tube-like arms
Lack suckers
Move by serpentine
motion of their
arms
Brittle Star
Class Echinoidea
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Include Sea urchins & sand dollars
Lack arms, but possess tube feet
Many species of urchins possess poisonous
spines used for defense
Echinoideans
Sand Dollar
Sea Urchin
Class Holothuroidea
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Include Sea
cucumbers
Are elongated
along oralanal axis
Lack spines
and have
reduced
endoskeleton.
Do possess
tube feet and
water vascular
system
Sea Cucumber
Class Crinoidia
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Ancient class of
animals
Include sea
lilies
Filter feeders
with arms
radiating from
mouth
Most are sessile,
but some can
move
Crinoids