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Echinoderms
Phylum Echinodermata
The body of an echinoderm can be divided radially into five equal
parts, somewhat like cutting a round cake into slices (also described
as being symmetical along five axes). Other unique echinoderm features
are their spiny skin, tube feet and their use of seawater to pump
up their bodies and move. All echinoderms have these basic features,
although at first glance they appear very different.
Shapes and spines
Let’s see how the various types of echinoderms shape up!
Sea stars usually have five arms. They have short or tiny spines.
Sea stars belong to Class Asteroidea.
 A
cushion star is a roundish sea star with very short arms.
 
Imagine a round cushion star with spines which may be long or thick.
This is what a sea urchin looks like! The round body of a sea urchin
can also be divided into five parts.
 A
flattened sea urchin with short spines is a sand dollar! It can still
be divided into five parts. A relative of the sea urchin called a
heart urchin is more egg-shaped with longer spines. It usually burrows
in the sand and is rarely seen above ground. Sea urchins, sand dollars
and heart urchins belong to Class Echinoidea.
 Imagine
a sea urchin that is long like a sausage without any obvious spines
and you have a sea cucumber! It too can be divided into five parts.
Sea cucumbers belong to Class Holothuroidea.
 A
brittle star is like a sea star with long and skinny arms. Brittle
stars belong to Class Ophiuroidea.
All these creatures are echinoderms and belong to the Phylum Echinodermata.
For more details on the Phylum Echinodermata
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