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C H I N O D E R M S |
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Echinoderms
as larvae are bilaterally symmetrical. As
they mature, they develop a pentagonal
symmetry. They are only found in the sea
(there are none on land or in fresh water).
Echinoderms mean "spiny skin" in Greek, but
not all, echinoderms have spiny skin. There
are over 6,000 species that can be organized
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Sea Stars: (group
name Stelleroidea) or Starfish, divided in
two sub-types:
The differences between the two sub-types
lies in how the arms connect to the central
disk. Ophiuroideas (like OPHIODERMA
LONGICAUDUM) have arms that do not connect
with each other. There is a distinct
boundary between arm and central disk.
Asteroideas have arms that are connected to
each other. Also, it is harder to tell with
asteroids where the central disk ends and
the arms begin.
The Sea Star have dermal branchiae on their
skin used to absorb oxygen as well as
Pedicellaria pincher-like organs used to
clean the surface of the skin. Barnacle
larvae could land on a sea star and start
growing if it were not for these organs.
Each ray of a sea star has a light sensitive
organ called an eyespot. Though it can not
see nearly as well as we do, sea stars can
detect light and its general direction.
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Given enough time, sea stars can grow back
arms that have been damaged or removed. For
a few species, the severed arm can grow back
into a complete sea star! For most sea
stars, however, a severed limb dies. Sea
stars eat many things.
A sea star's diet can include: barnacles,
snails, sea urchins, clams, and mussels. A
few species, such as the spiny star of the
North Atlantic, eat other sea stars! They
surround the shell and use the suckers on
their feet to pull the two shells (or
valves) apart. This creates an opening
between the two shells that is only .01
inches wide. Using this tiny gap, the sea
star puts its stomach into the clam's shell
and eats its insides. When it is done,
nothing is left but an empty shell. |
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Sea Urchins |
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Sea urchins, heart urchins, cake urchins,
and sand dollars belong to a sub-group of
echinoderms called enchinoidea.
These creatures have many sharp spines
pointing out in all directions that offer
protection from predators.
The spines are able to swivel towards a
predator because they are connected to
muscles. These animals have five paired rows
of tube feet with suckers. The mouth is on
the bottom, and the anus on top. The mouth
contains five teeth that point towards the
center. The tubed feet are used to move
along the bottom of the sea, where these
organisms use their teeth to eat algae. |
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Sea Cucumbers |
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Sea Cucumbers belong to a sub-category of
echinoderms called Holothuroidea.
Some members of the group look like
cucumbers you find in the supermarket. The
similarity ends there. Sea cucumbers lay on
their side at the bottom of the ocean. They
have five rows of tube feet running
lengthwise. Its mouth is surrounded by
tentacles. Unlike sea stars, the vascular
system is not filled with sea water.
Instead, sea cucumbers use a special body
fluid. |
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Sea cucumbers eat plankton and other organic
matter. Some position themselves in a
current that brings a steady supply of food,
and spend hours there. The tentacles open up
and collect food in the current. The sea
cucumber brings each tentacle to its mouth
to eat. Other sea cucumbers feed by sifting
through sand. Many sea cucumbers are
poisonous (though not for humans). If
injured, sea cucumbers can kill the fish in
the same aquarium as them. The sea cucumber
has can expel all of its internal organs!
This either scares off or satisfies
predators. The sea cucumber can then grow
another set of internal organs. Some other
sea cucumbers secrete a verysticky
substance as a defense mechanism. If you get
this glue on your body, you will not be able
to remove it without shaving your skin! |
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