Weird deep-sea animals discovered off the coast of Australia in the 1980s have finally been classified, and they’re like no animal alive today.
The newly described species, discovered between 400 and 1,000 metres below the ocean off the coast of Tasmania back in 1986, have been named Dendrogramma enigmatica andDendrogramma discoides. And they’re so unique that they don’t fit into any existing animal groupings - in fact, they appear to most closely resemble long-extinct organisms that lived in the Ediacaran period, between 635 and 540 million years ago.
The species have been described by scientists from the University of Copenhagan in PLOS ONE this week, and their discovery could completely rewrite the bottom branches of the animal family tree.
The multicellular organisms are just a couple of millimetres long and look like mushrooms, with a mouth at the end of their “stalk”. This is their only digestive opening, and it leads to a digestive canal that then branches out once it reaches the mushroom’s “cap”. They also have a dense layer of gelatinous material between their skin and inner stomach cell layers, the journal article explains.
The animals' mostly non-symmetrical body plan is unique, which means they’re not part of the Bilateria group, one of the main animal groupings that includes humans.
"Finding something like this is extremely rare, it's maybe only happened about four times in the last 100 years," co-author Jorgen Olesen told the BBC. "We think it belongs in the animal kingdom somewhere; the question is where."
The newly classified species do show some similarities to comb jellies, part of the Ctenophora phylum, as well as to Cnidaria, the phylum that includes jellyfish, corals and sea anemones. But they don’t fill all of the criteria to be included into either of these categories.
It’s possible that they may represent larval forms of existing species - or, interestingly, they may be surviving relative of ancient, long-extinct phyla.
Leonid Moroz, a neurobiologist at the University of Florida in St. Augustine, US, who wasn’t involved in the research, told Jennifer Frazer at National Geographic that if the new species is a descendent of early animals, the discovery could "completely reshape the tree of life, and even our understanding of how animals evolved, how neurosystems evolved, how different tissues evolved … It can rewrite whole textbooks in zoology."
Frazer explains for National Geographic:
“If the new animals are directly related to the ancient organisms, the find would be reminiscent of the discovery of the coelacanth fish, which had long been thought extinct, off the coast of South Africa in 1938. The new discovery also highlights how much of Earth's submarine realm remains unexplored, scientists say.”
Despite studying their anatomy, scientists still know very little about the species. After the animals were brought up, they were preserved in formalin and then ethanol, which makes genetic analysis almost impossible. They were then forgotten about until scientists started sorting the samples recently. Without any DNA analysis, scientists have little to classify the organisms from other than their appearance, and this means it’s extremely difficult to work out how the animals are related to other forms of life.
The researchers do believe, however, that the animals are free-living, as there were no signs they had been torn off something else. But they don’t seem to be able to swim and lack any obvious methods of propulsion. As Frazer explains, scientists believe the organisms feed by “ensnaring microbes in mucus secreted by the lobes surrounding their mouths”.
In the 28 years since these creatures were discovered off the coast of Tasmania, nothing remotely similar has ever been found. The researchers told BBC that they hoped people might become interesting in helping them after reading the paper.
"We published this paper in part as a cry for help," Oelson told BBC. "There might be somebody out there who can help place it.”
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