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Edrioasteroidea (Edrioasteroids)

      The Edrioasteroids are an extinct class of echinoderm that lived from the Ediacaran (if Arkarua was indeed an edrioaster) to the Permian periods of geologic time, about 300 million years ago. The animals usually consisted of a disk-like upper body made of many plates. The body plan for this class was simple: a main body (theca), composed of many small plates, a peripheral rim for attachment, and (in some species) a pedunculate zone for extension and retraction. Circling and sometimes attached to the body was a peripheral rim of plates. The main feature was the presence of five arms, or ambulacra, contained in the body wall radiating from the central mouth outwards. The ambulacra grew either curved or straight. When curved, they may all turn in the same direction or else one or two on the right side will curve opposite the others. The ambulacra are built of underlying floor plates that form the food groove and protective cover plates the roof the food groove. The anus was situated under the mouth region and was made of small triangular plates to form a cone-shaped area. The bottom surface of the theca is unplated. Edrioasteroid species are distinguished by differences in the ambulacral curvature, the relationships of the cover plates, and ornamentation. The mode of life was sessile; they were often attached via a stalk made of small plates to a hard object such as a carbonate hardground or shell. Several examples of epibiotic attachment have also been noted. In the discocystinids, the area between the body and peripheral rim could be extended and retracted; in so doing the two were separated. The peripheral rim became the base of the stalk which was attached to a surface. Underneath the body was a recumbent zone about 12 millimetres wide in the genus Giganticlavus, followed by the pedunculate zone attached to the peripheral rim of 12 millimetres.

Source:
http://en.wikipedia.org/wiki/Edrioasteroidea
Edrioasteroidea Billings, 1858 VK150
Edrioasteroidea Billings, 1858 MN52
Edrioasteroidea Billings, 1858 VK149
Edrioasteroidea Billings, 1858 BL114
Edrioasteroidea Billings, 1858 OZ255
Edrioasteroidea Billings, 1858 OZ266
Edrioasteroidea Billings, 1858 OZ267
Edrioasteroidea Billings, 1858 MN53
Edrioasteroidea Billings, 1858 MN54
Edrioasteroidea Billings, 1858 BL195
Edrioasteroidea Billings, 1858 MN58
Edrioasteroidea Billings, 1858Fatka et al., Fig. 8A BL203
Edrioasteroidea Billings, 1858 OZ253
Edrioasteroidea Billings, 1858 OZ260
Edrioasteroidea Billings, 1858 OZ299
Edrioasteroidea Billings, 1858 MN51
Edrioasteroidea Billings, 1858 OZ224
Edrioasteroidea Billings, 1858 OZ235
Edrioasteroidea Billings, 1858 OZ236
Edrioasteroidea Billings, 1858 OZ244
stromatocys
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Img. 86:

Virtual museum of the Czech Geological Survey, www.geology.cz, (C) Czech Geological Survey, 2011, v.0.99 [13.12.2011]