Biology
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28–4 Echinoderms
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28–4 Echinoderms
What Is an Echinoderm?
What are the distinguishing features of
echinoderms?
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28–4 Echinoderms
What Is an Echinoderm?
Echinoderms are characterized by spiny
skin, an internal skeleton, a water vascular
system, and suction-cuplike structures
called tube feet. Most adult echinoderms
exhibit five-part radial symmetry.
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28–4 Echinoderms
What Is an Echinoderm?
What Is an Echinoderm?
The skin of echinoderms is stretched over an
endoskeleton that is formed of hardened plates of
calcium carbonate.
Adult echinoderms typically have no anterior or
posterior end and lack cephalization.
The side in which the mouth is located is called the
oral surface, and the opposite side is called the
aboral surface.
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28–4 Echinoderms
What Is an Echinoderm?
Echinoderms are deuterostomes, animals in which
the blastopore develops into an anus.
Sea stars, sea urchins, and sand dollars are all
echinoderms.
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28–4 Echinoderms
Form and Function in Echinoderms
What functions are carried out by the
water vascular system of echinoderms?
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28–4 Echinoderms
Form and Function in Echinoderms
Form and Function in Echinoderms
Echinoderms have a system of internal
tubes called a water vascular system.
The water vascular system carries out
many essential body functions, including
respiration, circulation, and movement.
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28–4 Echinoderms
Form and Function in Echinoderms
Echinoderm Anatomy
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28–4 Echinoderms
Form and Function in Echinoderms
The water vascular system opens to the outside
through a sievelike structure called a madreporite.
madreporite
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28–4 Echinoderms
Form and Function in Echinoderms
A tube foot is attached to each radial canal.
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28–4 Echinoderms
Form and Function in Echinoderms
Tube feet act together to create enormous force
allowing echinoderms to “walk,” and pull open shelled
prey.
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28–4 Echinoderms
Form and Function in Echinoderms
Feeding
Echinoderms have several methods of feeding.
• Sea urchins use five-part jawlike structures to
scrape algae from rocks.
• Sea lilies use tube feet along their arms to
capture floating plankton.
• Sea cucumbers move across the ocean floor,
taking in sand and detritus.
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28–4 Echinoderms
Form and Function in Echinoderms
Sea stars usually feed on mollusks such as clams
and mussels.
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28–4 Echinoderms
Form and Function in Echinoderms
The sea star starts digesting the mollusk in its own
shell.
The sea star pulls its stomach and the partially
digested prey into its mouth.
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28–4 Echinoderms
Form and Function in Echinoderms
Respiration and Circulation
In most echinoderms, the thin-walled tissue of the
tube feet provides the main surface for respiration.
In some species, small outgrowths called skin gills
also function in gas exchange.
Circulation of needed materials and wastes takes
place throughout the water vascular system.
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28–4 Echinoderms
Form and Function in Echinoderms
Excretion
In most echinoderms, digestive wastes are released as
feces through the anus.
Nitrogen-containing cellular wastes are excreted primarily
in the form of ammonia.
This waste is passed into surrounding water through the
thin walled tissues of tube feet and skin gills.
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28–4 Echinoderms
Form and Function in Echinoderms
Response
Most echinoderms have a nerve ring that
surrounds the mouth, and radial nerves that
connect the ring with the body sections.
Most echinoderms have scattered sensory cells
that detect light, gravity, and chemicals released by
potential prey.
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28–4 Echinoderms
Form and Function in Echinoderms
Movement
Most echinoderms move using tube feet.
Sand dollars and sea urchins have movable spines
attached to the endoskeleton.
Sea stars and brittle stars use their arms for
locomotion.
Sea cucumbers crawl by using both tube feet and
the muscles of their body wall.
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28–4 Echinoderms
Form and Function in Echinoderms
Reproduction
Echinoderms reproduce by external fertilization.
Both sperm and eggs are shed into open water,
where fertilization takes place.
The larvae swim around for some time.
Larvae then swim to the ocean bottom and
develop into adults.
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28–4 Echinoderms
Groups of Echinoderms
What are the different classes of
echinoderms?
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28–4 Echinoderms
Groups of Echinoderms
Groups of Echinoderms
Classes of echinoderms include sea
urchins and sand dollars; brittle stars;
sea cucumbers; sea stars; sea lilies
and feather stars.
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28–4 Echinoderms
Groups of Echinoderms
Sea Urchins and Sand Dollars
Sea urchins and sand dollars have large, solid
plates that form a box around their internal organs.
Many are detritivores or grazers that eat large
quantities of algae.
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28–4 Echinoderms
Groups of Echinoderms
Sand dollars often burrow under layers of sand or
mud to protect themselves.
Some sea urchins wedge themselves in rock crevices
during the day.
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28–4 Echinoderms
Groups of Echinoderms
Brittle Stars
Brittle stars are common in many parts of the sea,
especially on coral reefs.
They are filter feeders and detritivores.
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28–4 Echinoderms
Groups of Echinoderms
Brittle stars have slender, flexible arms.
They shed one or more arms when attacked.
The detached arm keeps moving, distracting the
predator while the brittle star escapes.
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28–4 Echinoderms
Groups of Echinoderms
Sea Cucumbers
Most sea cucumbers are detritus feeders.
Herds roam across the deep-sea floor sucking up
organic matter and the remains of other animals
and plants.
Sea cucumbers look like warty, moving pickles.
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28–4 Echinoderms
Groups of Echinoderms
Sea Stars
Most sea stars are carnivorous, preying on
bivalves.
If a sea star is pulled into pieces, each piece will
grow into a new animal, as long as it contains a
portion of the central part of the body.
Sea stars move by creeping slowly along the
ocean floor.
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28–4 Echinoderms
Groups of Echinoderms
Sea Lilies and Feather Stars
Sea lilies and feather stars are common in tropical
oceans.
Many modern feather stars live on coral reefs,
where they perch on top of rocks and use their
tube feet to catch floating plankton.
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28–4 Echinoderms
Ecology of Echinoderms
Ecology of Echinoderms
A sudden rise or fall in the number of echinoderms
can cause major changes to populations of other
marine organisms.
Sea urchins help control the distribution of algae and
other forms of marine life.
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28–4 Echinoderms
Ecology of Echinoderms
Sea stars are important predators that help control
the numbers of other organisms.
The crown-of-thorns sea star has destroyed
extensive areas of coral in the Great Barrier Reef of
Australia.
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28–4
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28–4
The body plan of echinoderms is unusual in that
adult echinoderms
a. lack cephalization.
b. lack a nervous system.
c. lack cephalization and cannot move.
d. lack radial symmetry.
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28–4
The larvae of echinoderms are
a. not symmetrical.
b. radially symmetrical.
c. bilaterally symmetrical.
d. spherically symmetrical.
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28–4
The water vascular system of echinoderms
opens to the environment through the
a. tube feet.
b. siphon.
c. madreporite.
d. mouth.
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28–4
The crown-of-thorns sea star is a major threat to
a. marine algae.
b. coral reefs.
c. sea cucumbers.
d. bottom-dwelling fish.
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28–4
All of the following are echnioderms EXCEPT
a. sea stars.
b. horseshoe crabs.
c. sea cucumbers.
d. sand dollars and sea urchins.
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