Arkarua adami is a small disc shaped fossil, which has been identified as the earliest echinoderm. The classification was made because the fossil has a five-lobed central region, which can be interpreted as the five ambulacral grooves characteristic of echinoderms (Gehling 1987). Arkarua lacks a stereom or water vascular system, which makes their distinction as an echinoderm uncertain. It was first discovered in the Flinders Ranges in southern Australia, along with Dickinsonia, Tribrachidium, Cyclomedusa, and other Ediacaran animals (Taylor 2005). There is some difficulty in assessing the development of the first echinoderms, seeing as other stem groups, such as Hemalazoans and Helicoplacoidea, are not pentaradial but have a stereom.

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Gehling, JG. 1987. Earliest known echinoderm — a new Ediacaran fossil from the Pound Subgroup of South Australia. Alcheringa 11:337-345.

Taylor, C. 2005. Arkarua: All that is pentaradial is not Echinoderm. www.paleos.com. Accessed January 24, 2010.

The Virtual Fossil Museum. Phylum Echinodermata. Accessed January 24, 2010.