Shapes and spines
Letís 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 Subclass
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 Subclass Ophiuroidea.
A feather star is like a brittle star with many more arms. Instead
of lying flat against the surface, these arms are held up like branches
of a bush to gather food from the water. Feathers
stars belong to the Class Crinoidea.
All these creatures are echinoderms and belong to the Phylum Echinodermata.