Edrioasteroidea

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Edrioasteroids

An unidentified Edrioasteroid

Scientific classification

Kingdom:	Animalia
Phylum:	Echinodermata
Subphylum:	Pelmatozoa
Class:	Edrioasteroidea

The Edrioasteroids are an extinct class of echinoderm that lived from the Cambrian to the Carboniferous periods of geologic time. The animals usually consisted of a disk like upper body segment made of many plates. The body plan for this class was simple in that it is composed of a main body (theca), composed of many small plates. Circling and sometimes attached to the body was a peripheral rim, although this is also the base of attachment. The main feature is the five arms called ambulacra that are contained in the body area radiating from the mouth in the centre of the body outwards. The arms grow in a spiral pattern sometimes face the same direction. The anus situated under the mouth region and is made of small triangular plates to form a large cone shaped area. Differences in the ambulacral curvature and the plating covering the ambulacra and the mouth form the basis for telling apart different species of edrioasteroids. The mode of life was sessile, and to be attached via a stalk made of small plates to a hard object like a nautilus's shell or rocky or hardened sea floor

In the Discocystinid, the animals in life can be extended and retract, in so doing it separates the peripheral rim from the body. The peripheral rim becomes the base of the stork where the attachment to a surface happens. Underneath the body is the recumbent zone of about 12 mm wide in the genus Giganticlavus, followed by the pedunculate zone attached to the peripheral rim of 12 mm. The pedunculate roughly contains 28-35 column with 75 highly imbricate plates and is the largest section of some species bodies (Sumrall 1996).