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Members of this group are sea stars,
sea urchins, sea cucumbers and sand
Echinoderms have an internal skeleton
called a endoskeleton – made of
harden plates that makes the animal
bumpy and irregular texture.
Echinoderms only live in the sea.
What is an Echinoderm?
Adult echinoderms have no anterior or
posterior end and no head. They do
usually have 2 sides – the side with a
mouth (called the oral surface) and
the opposite side (the aboral surface).
Echinoderms have spiny skin, an
internal skeleton, a water vascular
system, and tube feet.
Most adult echinoderms have a 5 part
radial symmetry.
The larvae will usually have bilateral
Form and Function in Echinoderms
The water vascular system is filled with fluid
and carries out many body functions like
respiration, circulation, and movement.
It opens to the outside using the madreporite.
This is a sievelike structure. This will connect to
a ring canal that forms a circle around the
animals mouth. From the ring canal there are
radial canals that extend along the arms.
Attached to each radial canal is a tube foot.
This is like a suction cup. This allows the animal
to attach onto a surface. They have hundreds
of tube feet that allow them to walk and to
open prey like clams.
Sea urchins use jawlike structures to
scrape algae from rocks.
Sea lilies use tube feet to capture
floating plankton.
Sea cucumbers move across the ocean
floor taking in sand and detritus.
Sea stars eat mollusk like clams or
mussels. They will pry the shell open and
push their stomach out through their
mouth, digest the mollusk in its shell and
then pull its stomach and partially
digested prey into its mouth.
Respiration and Circulation
The tube feet provide the main
surface for respiration. Some species
have special gills also.
They use the water vascular system for
Most echinoderms do have an anus that gets rid of digestive waste.
They release cellular waste through their tube feet.
They do not have a well developed nervous system. They have a nerve
ring around the mouth and radial nerves down each body section.
Most echinoderms use tube feet to
move. Sand dollars and sea urchins
have moveable spines that attach to
the endoskeleton.
Sea stars and brittle stars use their arms
to move.
Sea cucumbers can crawl along the
ocean floor by tube feet and muscles
in the body wall.
Echinoderms reproduce by external fertilization. Both eggs and sperm and
shed into the water where fertilization will take place.
Sea Urchins and Sand Dollars
These animals have large, solid plates
that form a box around internal
Sand dollars will burrow under sand or
Sea urchins wedge themselves in rock
crevices and defend themselves with
long, sharp spines.
Brittle Stars
They have slender, flexible arms. They
can move quickly. They can also lose
one or more arms when attacked to
get away from a predator.
They are filter feeders and detritivores.
Sea Cucumbers
Are detritus feeders that suck up
organic matter.
When threatened they will spew their
guts to get away and then regrow
Sea Stars
The move by slowly creeping along
the ocean floor.
They are mostly carnivorous. They eat
When damaged they can grow new
Sea Lilies and Feather Stars
These are filter feeders that have long
feathery arms. They are mostly found
in tropical oceans on the ocean
Ecology of Echinoderms
Sea urchins help keep the amount of
algae in check.
Sea stars are important predators that
control clam and coral populations.
A crown of thorns sea star feeds on
coral on the Great Barrier Reef of
Australia. It has destroyed large areas
of coral.