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Biology
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28–4 Echinoderms
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What Is an Echinoderm?
What are the distinguishing features of echinoderms?
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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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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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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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7. Form and Function in Echinoderms
What functions are carried out by the water vascular system of echinoderms?
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8. 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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9. Form and Function in Echinoderms
Echinoderm Anatomy
The most distinctive system of echinoderms is the water vascular system, shown here in a sea star. The water vascular system, which extends throughout the body, functions in respiration, circulation, and movement.
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10. 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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11. Form and Function in Echinoderms
A tube foot is attached to each radial canal.
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12. 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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13. 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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14. Form and Function in Echinoderms
Sea stars usually feed on mollusks such as clams and mussels.
Photo Credit: ©Dorling Kindersley
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15. 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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16. 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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17. 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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18. 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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19. 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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20. 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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Groups of Echinoderms
What are the different classes of echinoderms?
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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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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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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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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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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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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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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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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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30. 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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31. 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
lack cephalization.
lack a nervous system.
lack cephalization and cannot move.
lack radial symmetry.
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28–4
The larvae of echinoderms are
not symmetrical.
radially symmetrical.
bilaterally symmetrical.
spherically symmetrical.
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28–4
The water vascular system of echinoderms opens to the environment through the
tube feet.
siphon.
madreporite.
mouth.
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28–4
The crown-of-thorns sea star is a major threat to
marine algae.
coral reefs.
sea cucumbers.
bottom-dwelling fish.
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28–4
All of the following are echnioderms EXCEPT
sea stars.
horseshoe crabs.
sea cucumbers.
sand dollars and sea urchins.
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38. END OF SECTION