Echinoderms
Odyssey Expeditions
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Jason Buchheim
Introduction
• Entirely marine
• Typically bottom
dwellers
• Generally posses
pentamerous radial
symmetry at some point
in life cycle (most can
be divided into five parts
around a central axis)
• Internal skeleton
composed of calcareous
ossicles (small plates)
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Introduction
• Sexes are generally
separate
• External fertilization
• Planktonic development
• Many have water
vascular system
(hydraulic system) for
food collection and
locomotion.
– Motion accomplished by
transmitting water
pressure.
Water vascular system in blue
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Classes
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Class Asteroidea
Class Ophiuroidea
Class Echinoidea
Class Holothuroidea
Class Crinoidea
Class Concentricycloidea
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Class Asteroidea
• Sea stars
• 1,800 species
• Typically have five
arms
• Regeneration
capabilities (in some a
new animal is formed)
• Mouth on bottom
(centrally located)
• Anus on top
NOAA
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Class Asteroidea
• Carnivores, detritivores,
opportunists, mud
swallowers
• Some can invert
stomachs out mouth to
surround prey
Organs in arms
– Bivalve predators slide
stomach between valves
and feed on the organism
while outside the body
• Organs distributed in
arms
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Class Asteroidea
• Two to four rows of podia (tube
feet) extend down each arm from
the mouth
Podia
– Used for prey capture and locomotion
• Podia extended by hydraulic
pressure
– Pressure generated by contraction of
bulblike ampulla
• In many, suckers are found on
podia
• Arms can twist and bend allowing
locomotion over varied terrain
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Class Ophiuroidea
• Brittle and Basket Stars
• Largest class (2,000 species)
• Mouth is centrally located on
the underside of body
• Highly mobile
• Long thin arms
• Organs in central disk not
arms
• Podia typically not
responsible for locomotion
• Use arms to push and pull
themselves along
NOAA
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Class Ophiuroidea
• Two distinct orders
• Order Ophiurae
– Brittle Stars
• Order Euryalae
– Basket Stars
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Order Ophiurae
• Five arms generally heavily
spined
• Calcareous plates (arm
shields) on arm tops allow
only lateral movement
• Arms break off easily
• Generally hide in crevices
and under rocks during the
day
• At night move into open to
feed
• Feed on detritus and small
animals
NOAA
NOAA
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Order Euryalae
• Have five arms that
continually divide into smaller
branches
• Lack arm shields which
enables full movement
• During day can be found
curled into a ball clinging to
gorgonians
• At night they stretch out their
arms to filter out plankton that
drifts over the reef
• Small spines and tube feet
move food to mouth
Jason Buchheim
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Class Echinoidea
• Sea urchins, sand
dollars and heart
urchins
• 1,000 species
• Moveable spins cover
theses animals
• No arms
• Circular or oval
• Globular or flattened
• Some display
secondary bilateral
symmetry
Jason Buchheim
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Class Echinoidea
• Ossicles are fused to create a solid
structure called a test
• Two basic groups:
– Regular Urchins (sea urchins)
– Irregular Urchins (heart urchins, sand dollars,
sea biscuit)
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Regular Urchins
• Sea Urchins
• Generally globular in
shape
• Covered with long
moveable spines
(some long and
pointed some short
and stubby)
• Anus on top
Jason Buchheim
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Regular Urchins
• Mouth centrally located
on underside
• Scrape algae with their
unique five teeth
arrangement call
Aristotle’s Lantern
• Important to the reef
because of the algae
control they provide.
Mouth
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Irregular Urchins
• Heart urchins, sand dollars,
and sea biscuits
• Evolved to specialize in
burrowing
• Small moveable spines
cover the body and are used
for burrowing
• Two orders:
USGS
– Order Spatangoida (heart
urchins)
– Order Clypeasteroida (sand
dollars and sea biscuits)
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Order Spatangoida
• Heart urchins
• Oval dome-like in shape
• Feed on organic
materials in the
substrate
• Mouth (lacks Aristotle’s
Lantern) in front and
anus in back
• Typically found buried in
the substrate
• May be seen at night
NOAA
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Order Clypeasteroida
• Sand dollars and sea
biscuits
• Flattened disk shape
• Mouth centrally
located on the
underside with
Aristotle’s Lantern
• Anus found towards
rear
• Live buried in the sand
USGS
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Class Holothuroidea
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Sea cucumbers
Tubular in shape
1,000 species
Mouth in front and anus in
rear
• Most feed on organics
found in the sand that
they consume
• Some filter feed
Odyssey Expeditions
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Class Holothuroidea
• Tube feet cover the bottom surface
• If threatened can expel most of their guts
• Can regenerate these guts
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Class Crinoidea
• Feather stars (Crinoids)
• Oldest echinoderms (living
fossils)
• 600 species
• Five arms that fork to give
ten or more
• Look like feathers
• Arms are sticky and sweep
water for food particles
• Can regenerate arms
Jason Buchheim
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Class Crinoidea
• Can move short
distances
• Some swim with arms
• Others walk on legs
called cirri
Jason Buchheim
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Resources
•
Barnes, Robert D. and Edward Ruppert. Invertebrate Zoology: Sixth Edition.
Fort Worth: Saunders College Publishing, 1994
•
Humann, Paul and Ned Deloach. Reef Creature Identification: Florida
Caribbean Bahamas. Florida: New World Publications, Inc., 2003
•
Kinsella, John, Drew Richardson and Bob Wohlers. Life on an Ocean
Planet. California: Current Publishing Corp., 2006
•
Taylor, Walter K. and Robert L. Wallace. Invertebrate Zoology: A
Laboratory Manual Sixth Edition. New Jersey: Prentice Hall, 2002
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