“Spiny Skin”
~7,000 species
Sea stars, sand dollars, and sea urchins
A thin skin covers a hard calcareous platelike exoskeleton.
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• They are divided into six classes:
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Asteroidea (sea stars)
Ophiuroidea (brittle stars)
Echinoidea (sea urchins and sand dollars)
Crinoidea (sea lilies and feather stars)
Holothuroidea (sea cucumbers)
Concentricycloidea (sea daisies)
Major Characteristics
All are aquaticmarine
Tube feet:“suction cup”
locomotion,
feeding, and gas
exchange. Sand
dollars and sea
urchins have
moveable spines.
Animation
The bulb at the top of the tube
foot is called the ampulla.
•Have water vascular
system
•A network of
hydraulic canals which
branch into extensions
(tube feet)
•Open to the outside
through the
madreporite plate.
Usually body in
multiples of five
All have an endoskeleton consisting of calcareous plates
bearing spines
• Bilaterally symmetrical
larvae metamorphose into
radial adults.
-larva of the starfish
Feeding:
•Various methods
Sea Star:
Pushes stomach out through its mouth (which is on
the underside) into a clam and then digests.
Waste excreted
through the anuswhich is on top.
Obtain oxygen
through diffusion
• Sea urchins and sand dollars have no arms, but they
do have five rows of tube feet that are used for
locomotion.
– Sea urchins can also move by pivoting their long spines.
– The mouth of an urchin is ringed by complex jawlike
structures adapted for eating seaweed and other foods.
– Sea urchins are roughly
spherical, while sand
dollars are flattened
and disk-shaped.
• Sea stars and some other echinoderms can
regenerate lost arms and, in a few cases,
even regrow an entire body from a single
arm.
• Sea lilies -attached to the substratum by stalks and
• Feather stars -crawl using their long, flexible arms.
• Both use their arms for suspension-feeding.
• Sea cucumbers
• They lack spines, the hard endoskeleton is much
reduced in most.
• Some tube feet around
the mouth function as
feeding tentacles for
suspension-feeding
or deposit feeding
•Ecology:
•Major food source for other marine animals
•Carnivorous echinoderms help control
populations of clams
•“Crown of Thorns” sea star destroys coral
reef systems.
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Echinoderms
A. Echinoderms Have a Spiny Skin
1. About 6,000 species of echinoderms are in phylum Echinodermata.
2. Modern echinoderms are all marine.
3. All have an endoskeleton consisting of calcareous plates bearing spines.
4. Class Crinoidea includes 600 species of crinoids; includes stalked sea lilies and motile
feather stars.
5. Class Holothuroidea has 1,500 species of sea cucumbers; they have a long leathery body
and feed
by tentacles about the mouth.
6. About 950 species of sea urchins and sand dollars are in class Echinoidea; they possess
spines for
locomotion, defense, and burrowing.
7. About 2,000 species of brittle stars are in class Ophiuroidea; they have a central disk
from which
long, flexible arms radiate.
8. Class Asteroidea contains 1,500 species of sea stars (starfishes).
B. Sea Stars
1. Sea Stars are common along rocky coasts; they feed on clams, oysters, and other
bivalves.
2. Five-rayed body has an oral (mouth) and aboral (upper) side.
3. Various structures project through the body wall.
a. Spines project from the endoskeletal plate through the thin dermis.
b. Pincer-like pedicellarie keep the surface free from particles.
c. Gas exchange is conducted by skin gills.
d. On the oral surface, each arm has a groove lined with tube feet.
4. Sea stars feed by everting the stomach.
a. A sea star positions itself over a bivalve and attaches tube feet to each side of the
shell.
b. Working tube feet alternatively, it pulls a shell open; a small crack allows it to insert a
cardiac stomach.
c. Stomach enzymes begin digestion of a bivalve while it is trying to close its shell.
d. Partially digested food is taken into a pyloric stomach for full digestion.
e. A short intestine opens at the anus on aboral side.
5. In each arm is a developed coelom containing paired digestive glands and
male or female gonads.
6. Nervous system is a central ring with radial nerves in each arm.
7. A light-sensitive eyespot is at the end of each arm.
8. Locomotion depends upon a water vascular system.
a. Water enters on aboral side through a sieve plate (madreporite).
b. Water passes through a stone canal to a ring canal and into radial
canals in each arm.
c. Radial canals feed into lateral canals extending into tube feet;
each has an ampulla.
d. Contraction of an ampulla forces water into the tube foot,
expanding it; when the foot touches a
surface, the center withdraws forming a suction and adhering to
surfaces.
9. Echinoderms lack a complex respiratory, excretory, or circulatory
system.
a. Fluids within a coelomic cavity diffuse substances and gases.
b. Gas exchange occurs across skin gills and tube feet.
c. Nitrogenous wastes diffuse through coelomic fluid and across a
body wall.
d. Cilia on a peritoneum lining the coelom keep coelomic fluid moving.
10. Sea stars reproduce both sexually and asexually.
a. If body is fragmented, each fragment can regenerate a whole
animal.
b. Sea stars spawn and release either eggs or sperm at the same
time.
c. The bilateral larvae undergoes metamorphosis to become a
radially symmetrical adult.
System Type
Echinoderm System
MuscularSkeletal
A Echinoderm has an inner skeleton. It travels by means of many tube
feet.
Digestion
A Echinoderm has a mouth and stomach area. Some have a mouth on the
bottom and an anus on the top.Starfish can actually turn their stomachs
outside of their body and insert it into its prey's such as a clam.
Echinoderms have a relatively big gut area.
Nervous
A Echinoderm has eyespots which can detect light. Their eyespots are
not as sharp as human eyes. It generally has a poorly developed nervous
system.
Circulation
A Echinoderm has water pumped through its body as part of its very
simple circulation system.
Respiration
A Echinoderm uses some of the bumps or spines on its surface to take in
oxygen. It has a gill structure to take in the oxygen. It has a poorly
developed respiratory system.
A Echinoderm is a male or female. The males and females discharge their
eggs and sperm into the water where they are fertilized. A female can
Reproduction release one hundred million eggs at once. If a piece of certain
echinoderms is chopped off, a new piece or even a new echinoderm can
regrow.
Excretion
A Echinoderm has a simple excretory system.
Symmetry
A Echinoderm has radial symmetry.