Deep Sea "Mushroom" Shaped Life Form

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.

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We think it belongs in the animal kingdom somewhere, the question is where”

Jorgen Olesen
University of Copenhagen
These organisms, too, have proven difficult to categorise and some researchers have even suggested they were failed experiments in multi-cellular life.

The authors of the paper recognise two new species of mushroom-shaped animal: Dendrogramma enigmatica and Dendrogramma discoides. Measuring only a few millimetres 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 recognised only recently, after sorting of the bulk samples collected during the expedition.

"Finding something like this is extremely rare, it's maybe only happened about four times in the last 100 years," said co-author Jorgen Olesen from the University of Copenhagen.

He told BBC News: "We think it belongs in the animal kingdom somewhere; the question is where."

The system used to group every life form on Earth encompasses several levels, or taxonomic ranks.

A domain is the highest taxonomic rank and below that is a kingdom. Traditionally, biologists have recognised five or six kingdoms, including animals, plants, fungi and bacteria.

Kingdoms are divided into phyla, which are grouped according to similarities in general body plan.