Download Echinoderms

Echinoderms
“Life with Spiny Skin”
A Radical Radial Change
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Worms, mollusks, and
arthropods all have
bilateral symmetry.
So do echinoderm larvae.
What kind of symmetry
do adult echinoderms
have?
Radial symmetry
What other animal phyla
display radial symmetry?
Bipinnaria larvae (sea star)
Five Alive
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2
1
3
5
4
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Most echinoderms
show pentamerous
radial symmetry.
This means there are
usually five arms (or
legs) or they are
found in multiples of
five.
Spiny Skin – but only the skin!
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Echinoderm means “spiny skin.”
Echinoderms typically have:
well developed digestive tracts
 well-developed coelom
 Internal skeleton called an endoskeleton
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Spines or bumps are anchored in the
endoskeleton but may protrude through the
skin.
What No Top and Bottom?
Echinoderms have no head; therefore, there is
no anterior or posterior.
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Rather than use
the term dorsal,
the side of the
echinoderm
without a
mouth is called
the aboral side.
aboral
oral
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The
echinoderm
mouth is
usually on the
bottom. This
is termed the
oral side.
Water vascular system
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A network of water-filled canals that function in
movement, feeding, and excretion.
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Water enters the
echinoderm through the
madreporite (mother pore)
or sieve plate.
Water is then forced
through individual tube
feet allowing them to
move.
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Water Vascular System
Water Vascular System
Types of Echinoderms
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Approximately 7,000 species – all marine
Located from the poles to the tropics
Five major classes
Asteroidea (sea stars) – not starfish –they are
definitely not “fish”
 Ophiuroidea (brittle stars)
 Echinoidea (sea urchins and sand dollars)
 Holothuroidea (sea cucumbers) – not a vegetable!
 Crinoidea (feather stars and sea lilies)
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Asteroidea
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Endoskeleton rather flexible to allow for movement.
Most have five arms radiating from a central disk.
Asteroidea
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Hundreds of
tube feet are
found in
channels called
ambulacral
grooves
radiating from
the central disk.
Asteroidea
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Naturally the anus is on
the aboral (top) side.
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Aboral surface covered
with pedicellariae – tiny
pincer like organs that
keep the sea star clean.
Asteroidea
Ophiuroidea
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Ophiothrix spiculata
Brittle stars
Most numerous class of
echinoderms.
Characterized by thin,
very flexible arms.
Eat particulate matter on
the ocean floor.
No anus.
Often hidden.
Ophiuroidea
Echinoidea
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Sea urchins & sand
dollars
Endoskeleton is a rigid,
shell-like “test.”
Covered with movable
spines – used in
locomotion and defense.
Grazers – feed on algae
and dead organic matter.
aboral
oral
Echinoidea
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An intricate mouth and jaw system called
the Aristotle’s lantern consists of 50 bones
and is controlled by over 60 muscles.
Echinoidea
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Not all “urchins” have prominent spines.
Sand dollars have flattened bodies and tiny spines.
They use a mixture of mucus and physics
(Bernoulli’s principle) to capture food.
Holothuroidea
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Sea cucumbers
Elongated version of
the pentamerous body
plan.
Lie on side with five
rows of tube feet on
bottom.
Tough skin supported
by calcareous spicules.
Holothuroidea
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Tube feet near the
mouth are modified into
tentacles for feeding.
Some burrow and
capture food while
others ingest sand and
filter out detritus and
small organisms.
Holothuroidea
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Defense
 Secrete
toxins
 Discharge sticky
toxic filaments
 Eviscerate – eject a
portion of the
internal organs to
confuse an attacker.
Sea cucumber evisceration
Crinoidea
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Feather stars, basket stars, sea
lilies
Suspension feeders
Oral surface on top
Can have from 5 to 200 arms!
Have claw like appendages that
hold the aboral surface to the
substrate.
Crinoidea