The Echinoderm
Echinoderms have an external skeleton
with spines. Usually they have five arms.
Spaces between the arms may be filled in.
Body
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.
Arms
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
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.
Pinegreenwoods Montessori
Montessori Zoology
