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MONTESSORI ZOOLOGY : External Parts of Echinodermata

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The Echinoderm

Echinoderms have an external skeleton
with spines. Usually they have five arms.
Spaces between the arms may be filled in.


 The body of the echinoderm has a central 
cavity. Other body parts are arranged around 
the body like the spokes of a wheel.
This star-like arrangement of the body
is called radial symmetry.

Aboral Surface

The top side of the echinoderm
is called the aboral surface.

Oral Surface

The mouth is in the center of
the oral surface of the echinoderm.

Central Disk

The central disk is the center
portion of many echinoderms.

Tube Feet

 Tube feet are tiny, tube-like structures.
Tube feet project from the body on
the oral surface of many echinoderms.


The arms of some echinoderms are long 
extended parts of the body. Arms are used to 
move and catch prey. Some echinoderms have 
five arms (starfish, brittle stars); some have
many more arms (basket stars, sea lilies); 
and some have arms inside their bodies
( sea urchins, sand dollars).


Spines project from the skeleton of the
echinoderm. These spines protect the animal
from its enemies. Some echinoderms have
sharp spines (sea urchins) and some have
blunt spines (starfish, sea cucumbers).

Ambulacral Grooves

Ambulacral grooves are prominent furrows 
in each arm, extending from the central 
cavity to the tip. Tube feet protrude from the
 ambulacral grooves of the echinoderm.


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Montessori Zoology