Dickinsonia
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Dickinsonia is an ancient ovoid fossil with somewhat radial tubes from a (sometimes missing) central ridge. The ends are different, with close spaced tubes on one end and larger, more widely spaced tubes on the other. However, it is unclear whether there is an actual head and tail.
Dickinsonia somewhat resembles the Polychaete worm Spinther. It is thought by some possibly to be an annelid worm. It has also been described as a jellyfish, coral, sea anemone, an arthropod, a bacterium, a new phylum, a new kingdom, and as an alien animal. Four species are known; Dikinsonia costata, Dikinsonia lissa, Dikinsonia tenuis, and Dikinsonia rex, the last of which can be as large as 43 cm.
Dickinsonia is known from neoproterozoic beds in both the Alice Springs and Ediacara regions of Australia, as well as Rajastan, Podolia, and the White Sea region of Russia. Dickinsonia is generally regarded as a member of the Vendazoa -- a group of somewhat obscure animals that thrived just before most of the modern multicellular animal phyla appeared. It is unclear if the Vendazoa are plants, animals, or something else entirely. Another vendazoan known as Marywadea somewhat resembles Dickinsonia and may be related.
A picture of Dickinsonia can be found at http://www.yale.edu/ypmip/taxon/vendo/35467.html