Dickinsonia is the name given to range of extinct organisms which have left distinct fossil records. Since 1947, a total of nine species have been described. To date, the highly unusual nature of the organisms has left paleobiologists unable to properly classify them - to the extent that it's not even yet certain if they were an animal or a plant. They were apparently in some ways mobile, however, they lack any convincing evidence for a mouth, anus or gut, and appear to have fed by absorption via their bottom surface.
Also unknown is whether they were an ancestor of some currently living creatures, or whether they were a distinct, and now lost, biological kingdom.
“The affinities of Dickinsonia are uncertain. It has been variously interpreted as a jellyfish, coral, polychaete worm, turbellarian, mushroom, xenophyophoran protist, sea anemone, lichen, and even a close ancestor of the chordates.” Source: Wikipedia