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Strange deep-sea life form discovered

By: Lisa Robinson, Category: Science, Date: 04 Sep 2014

A new type of marine animal resembling mushroom-shaped jellyfish has scientists stumped.

Dendrogramma enigmatica

Jørgen Olesen © Jørgen Olesen

Scientists have discovered two new species of strange mushroom-shaped marine animals off the coast of Australia.

Although collected in 1986 by Danish zoologist Jean Just during a deep sea sampling expedition off Tasmania, the specimens sat in storage for decades until they could be examined properly.

Bizarre

The multicellular animals have a stalk and a broad, flat disc up to 17 mm in diameter. The mouth is located in the base of the stalk, with a simple gastrovascular system running centrally up through the stalk (pharynx) and branching out through the disc.

The research, published in the online journal PLOS ONE on 3 September, was led by Dr Just who has worked as a visiting curator at the Australian Museum and continues to maintain a strong interest in its collections.

Dr Just and his team have classified the mushroom-shaped organisms in a new genus, Dendrogramma, named after the branching of the gastrovascular system in the disc. Within this genus are two species – D. enigmatica, aptly named since little is known about this bizarre organism, and D. discoides, which alludes to the shape of the disc.

Determining where these organisms belong in the tree of life has been made more difficult by the way they were preserved when collected. Using general fixing and preserving fluids has unfortunately made the specimens brittle and unsuitable for genetic analysis.

The researchers think that Dendrogramma is similar to comb-jellies (Ctenophora), corals and jellyfish (Cnidaria), yet there is no unique characteristic to classify them in either of these. Dendrogramma is also similar to certain fossils from the Precambrian Ediacara fauna 600 million years ago.

Cryptic

Researchers found no additional specimens in a follow-up expedition in 1988, which is not hard to believe, according to Dr Stephen Keable, Collection Manager for Marine Invertebrates at the Museum.

‘Sampling the bottom of the ocean using coarse nets drags up all kinds of things which have to be processed. It’s easy for tiny samples like these to be missed because it’s unclear what the animals are, so they can easily be overlooked and discarded’, he said.

Dr Keable says this latest finding highlights that very little is known about the deep sea environment. ‘It’s a difficult environment to sample, and marine invertebrates are such small and cryptic animals that processing them is challenging and takes a long time’, he said.

Lisa Robinson, Communications Intern

Further reading

Just J, Kristensen RM, Olesen J (2014) Dendrogramma, New Genus, with Two New Non-Bilaterian Species from the Marine Bathyal of Southeastern Australia (Animalia, Metazoa incertae sedis) – with Similarities to Some Medusoids from the Precambrian Ediacara. PLoS ONE 9(9): e102976.