A mushroom-shaped sea animal discovered off the Australian coast has defied classification in the tree of life.

 

A team of scientists at the University of Copenhagen says the tiny organism does not fit into any of the known subdivisions of the animal kingdom.

 

Such a situation has occurred only a handful of times in the last 100 years.

 

The organisms, which were originally collected in 1986, are described in the academic journal Plos One.

 

The authors of the article note several similarities with the bizarre and enigmatic soft-bodied life forms that lived between 635 and 540 million years ago - the span of Earth history known as the Ediacaran Period.

 

These organisms, too, have proven difficult to categorize and some researchers have even suggested they were failed experiments in multi-cellular life.

 

The authors of the paper recognize two new species of mushroom-shaped animal: Dendrogramma enigmatica and Dendrogramma discoides. Measuring only a few millimeters in size, the animals consist of a flattened disc and a stalk with a mouth on the end.

 

During a scientific cruise in 1986, scientists collected organisms at water depths of 400m and 1,000m on the south-east Australian continental slope, near Tasmania. But the two types of mushroom-shaped organisms were recognized only recently, after sorting of the bulk samples collected during the expedition.

 

The new organisms are multicellular but mostly non-symmetrical, with a dense layer of gelatinous material between the outer skin cell and inner stomach cell layers.

 

The researchers did find some similarities to other animal groupings, such as the Cnidaria - the phylum that comprises corals and jellyfish - and the Ctenophora, which includes the marine organisms known as comb jellies. But the new organisms did not fulfil all the criteria required for inclusion in either of those categories.

 

One way to resolve the question surrounding Dendrogramma's affinities would be to examine its DNA, but new specimens will need to be found. The original samples were first preserved in formaldehyde and later transferred to 80% alcohol, a mode of treatment that prevents analysis of genetic material.