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Arkarua
''Arkarua adami'' is a small, Precambrian disk-like fossil with a raised center, a number of radial ridges on the rim, and a five-pointed central depression marked with radial lines of 5 small dots from the middle of the disk center. Fossils range from 3 to 10 mm in diameter.
''Arkarua'' is known only from the Ediacaran beds of the Flinders Ranges in South Australia. The generic name refers to Arkaru, a mythical giant snake of the local Aboriginal people.〔Gehling, J.G. 1987. Earliest known echinoderm — a new Ediacaran fossil from the Pound Subgroup of South Australia. Alcheringa 11:337-345.〕
==Classification==
All known specimens of ''Arkarua'' are casts that give no clue to the internal structure, making classification problematic. Because of ''Arkaruas pentamerous symmetry, it is tentatively placed within phylum Echinodermata. Because of its flattened disk- or button-shape, coupled with its pentamerous symmetry, some claim that it can be further classified into the Edrioasteroidea, a class of the echinoderms.
However, it lacked a feature present in later echinoderms: the stereom, a unique crystalline form of calcium carbonate from which their skeletons are built.〔Paul D. Taylor, David N. Lewis ''Fossil Invertebrates'' Harvard University Press, 2007 ISBN 0-674-02574-1 pages 163-164〕
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