Aliens in the shape of unclassifiable mushroom-shaped creatures have been discovered in the ocean depths off Australia.

Two species of the strange organisms were found that could not be placed in any existing phyla, the large families of living things that include vertebrates and flowering plants.

The animals, known as Dendrogramma, consist mainly of an outer skin and inner stomach separated by a dense layer of jelly-like material.

Scientists suspect they are related to ancient extinct life forms that lived 600 million years ago and may have represented a failed early attempt at multicellular life.

They were discovered in a collection of organisms dredged up in 1986 from depths of 400 and 1,000 metres on the south-east Australian continental slope.

Researchers have only now isolated the two species of Dendrogramma described in the latest edition of the online journal Public Library of Science ONE.

The species have been named Dendrogramma enigmatica and Dendrogramma discoides.

Danish lead scientist Dr Jorgen Oleson, from the University of Copenhagen, said: "New mushroom-shaped animals from the deep sea have been discovered which could not be placed in any recognised group of animals.

"Two species are recognised and current evidence suggest that they represent an early branch on the tree of life, with similarities to the 600 million-year-old extinct Ediacara fauna."

A new attempt may now be made to find other specimens of the mushroom animals.