Some unusual marine organisms don’t seem to fit anywhere in the animal classification scheme. Are they remnants of the Ediacaran fauna that preceded the Cambrian explosion?

They were found in 1986 in deep waters off the coast of Australia: bizarre, striped, mushroom-shaped creatures. Pickled away in jars at the time, they escaped further study — till now. Scientists want to know what on earth they are. The hunt is on for more living specimens! The paper in PLOS ONE sets the stage:

A new genus, Dendrogramma, with two new species of multicellular, non-bilaterian, mesogleal animals with some bilateral aspects, D. enigmatica and D. discoides, are described from the south-east Australian bathyal (400 and 1000 metres depth). A new family, Dendrogrammatidae, is established for Dendrogramma. These mushroom-shaped organisms cannot be referred to either of the two phyla Ctenophora or Cnidaria at present, because they lack any specialised characters of these taxa. Resolving the phylogenetic position of Dendrogramma depends much on how the basal metazoan lineages (Ctenophora, Porifera, Placozoa, Cnidaria, and Bilateria) are related to each other, a question still under debate. At least Dendrogramma must have branched off before Bilateria and is possibly related to Ctenophora and/or Cnidaria. Dendrogramma, therefore, is referred to Metazoa incertae sedis. The specimens were fixed in neutral formaldehyde and stored in 80% ethanol and are not suitable for molecular analysis. We recommend, therefore, that attempts be made to secure new material for further study. Finally similarities between Dendrogramma and a group of Ediacaran (Vendian) medusoids are discussed.

The paper does little more than document the creatures, show pictures and diagrams, and then encourage explorers to go find more living specimens, so that their genomes can be studied. Nature News calls this "extremely exciting" and "like the discovery of a treasure":

New species are discovered all the time — the 1984 Australian expedition alone yielded somewhere between 200 and 300. But finding one that does not fit within the known tree of life has happened only two or three times in the past 15-20 years, says Andreas Hejnol, a developmental biologist at the Sars International Centre for Marine Molecular Biology in Bergen, Norway.

If these turn out to be remnants of Ediacaran colonies, they will set records as some of the oldest "living fossils" on earth! What were these creatures doing not evolving for over 500 million years?

Caution should be exercised before making claims about these organisms till more specimens can be gathered and their genomes sequenced. It will be very interesting to see what relationships, if any, these creatures have with the body plans that appeared suddenly in the Cambrian explosion.

We shouldn’t be all that surprised if they turn out to be "living fossils" from Ediacaran times, though: several of the original Cambrian animals, like comb jellies, appear virtually identical to living forms today.

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