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Subclasses in subphylum Asterozoa


Asterozoans (Class Stelleroidea) are grouped into three subclasses;

Class Stelleroidea

Subclass Asteroidea

Subclass Ophiuroidea

Order Euryalae

Order Ophiurida

Subclass Somasteroidea


Subclass Asteroidea

The first true asteroids are of early Arenig age.
This subclass contains the asteroids commonly known as star fish. However due to the fact they are not fish, most biologists encourage the use of the term sea stars.


Subclass Ophiuroidea

There are two orders;
Ophiurida (Ordovician - Recent) - the arms only bend in the horizontal plane
Euryalae (Carboniferous to Recent) - the arms can move in all directions, and are often climbers.

Also known as brittle stars these asterozoans are instantly identifiable by their thin snake-like arms, shown in the above picture. These have contributed to their great success, as they use sinuous movements of their arms to move.


Subclass Somasteroids

Tremadocian - Middle Ordovician
The earliest known sea stars belong to this subclass, which was a short-lived group that was probably the common ancestor to both Asteroidea and Ophiuroidea.

continue to learn more about the anatomy of sea stars, or

return to the major subclasses.

Author: Elizabeth Sweet
Last updated: 22nd November 2005
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