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Echinoderms
Name
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Echino = spiny
Dermis = skin
Animals with bumpy and irregular
texture
General Characteristics
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Echinoderms have spiny skins.
Internal skeleton
They have radial symmetry (usually 5 parts)
They lack body segmentation.
Water vascular system
Tube feet = Suction cup like structures
There are more than 7000 species of
Echinoderms.
If they are radially symmetric, why are they
considered a “higher” evolutionary phyla?
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Echinoderms are the “highest”
invertebrates  the most closely
related to humans!
The larvae is bilaterally symmetric
They are deuterostomes
Nervous System
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Decentralized nervous system
 Radial nerves run under the ambulacra (legs)
 Central nerve ring surrounds the gut
 Eyespots that can detect light
 No specialized sensory organs
 and no definitive brain
Circulatory Structures
-A Echinoderm has water pumped through its body as part of
its very simple circulation system
-no specific structures for the circulatory system
Digestive/Excretory System
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Tubes grab onto food -> invert their stomach -> secrete/squirt juices (enzymes) that
digest -> reabsorb digested food through mouth under the center -> wastes out the aboral
anus
Locomotion
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Vascular system consist of a network of hydraulic canals
branching into extensions called papullae (tube feet), which
provides:
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slow movement
feeding
and gas exchange
Tube feet uses hydraulics to create negative pressure which acts as a
suction force.
SENSORY STRUCTURES
-rudimentary senses including:
-light sensitive eyespots
-sensory tentacles (modified tube feet) at the tips of the arms
-small patches of cells sensitive to chemicals or touch.
Reproductive System
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Most are dioecious, with separate male and female individuals, but
some are hermaphrodites.
Each arm contains two gonads, which release gametes through
openings called gonoducts, located on the central body between the
arms.
Types of Echinoderms
Echinoderm Classes
 Class:
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Crinoidea
Holothuroidea
Echinoidea
Ophiuroidea
Asteroidea
Class Crinoidea
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Sea lilies and feather stars
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Arms branched attached by a stalk or free-moving. The
mouth and anus on oral surface. No spines. Filter feeders.
Most primitive. Sedentary life, attached to substrate.
fossils
Class Holothuroidea
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Sea cucumbers
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Elongated body with no arms or spines. Skeleton only of
microscopic plates mouth ringed by retractile tentacles(modified
tube feet). Detritus feeders. Move in herds.
Class Echinoidea
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Sea urchins and sand dollars
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Skeleton rigid (plates fused), mouth parts present, mouth with 3jaws. Spines movable. Detritivores and grazers.
Sand dollar
Sea urchin
Mouth parts
Sea biscuit
aboral surface oral surface
aboral
oral
endoskeleton
Aristotle’s lantern
Class Ophiuroidea
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Brittle stars and basket stars
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Arms distinct from central disc. Tube fee without suckers
(not used in locomotion). Can move very fast to escape
predators and can leave an arm if caught (detached arm
keeps moving to distract predators)
Basket star
Aboral surface
Oral surface
Class Asteroidea
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Sea stars and starfish
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Arms are not sharply distinct from central disc. Tube feet
with suckers (used for locomotion). Carnivores (extreme
predators). Can regenerate from parts.
Aboral surface
Aboral surface Oral surface
Oral surface
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Life Series Time Lapse Echinoderms