A mushroom-shaped marine animal discovered off the coast of Australia is challenging any classification on the species table.
A team of scientists from the University of Copenhagen say the tiny organism does not fit into any of the known subdivisions of the animal kingdom.
Such a situation has occurred in very few cases in the last 100 years.
The organisms, which were originally collected in 1986, are described in the academic journal Plus one.
The authors of the article note several similarities with the rare and enigmatic life forms that inhabited the planet some 635 million years ago, in the era known as the Ediacaran Period.
Organisms from that evolutionary period have also been difficult to classify, and some researchers suggest that they were unsuccessful experiments on multicellular life forms.
The study authors accept two new mushroom-shaped animal species: Dendrogramma enigmatica Y Discoid dendrogramma.
They are only a few millimeters long and consist of a flattened disk with a stem and a mouth at its end.
During a scientific voyage in 1986, researchers collected organisms in the ocean at depths between 400 meters and 1,000 meters on the southern part of the Australian continental shelf, near Tasmania. However, the two types of mushroom-shaped organisms were only recently recognized after reviewing the samples collected on that expedition.
«Discovering something like this is extremely rare, perhaps only four times in the last 100 years,» says study co-author Jorgen Olesen of the University of Copenhagen.
«We think it fits somewhere in the animal kingdom, the question is where,» he told the BBC.
The system used to group each form of life on Earth encompasses various levels or taxonomic ranks.
A domain is the highest taxonomic rank and below it is a kingdom. Traditionally, biologists have recognized five or six kingdoms, including animals, plants, fungi, and bacteria.
The kingdoms are divided into phyla, which are grouped according to the similarities of the bodies.
«What we can say about these organisms is that they do not belong to the bilaterals (bilateria),» says Olesen.
The bilateria represents one of the most important animal phyla, whose members share a bilateral symmetry (their bodies are divided vertically into left and right halves that mirror each other). Human beings are within this phylum.
The new organisms are multicellular but not symmetrical, with a dense layer of gelatinous material between the outer skin and the inner cell layers of the stomach.
The researchers found some similarities to other groups of animals, such as the Cnidaria phylum, which includes corals and jellyfish, and the Ctenophora, which includes marine organisms known as comb jellies. But the new organisms did not meet all the requirements required for inclusion in any of those categories.
Olesen says the new animals could either be a very early branch on the tree of life, or be intermediate between two different animal phyla.
He recognized that they might eventually find their way into an existing group, because there is still so little information about the biology of the Dendrogram.
One way to resolve the question surrounding the affinities of the dendrogram I’d test his DNA, but he’d need new samples. The original samples were first preserved in formaldehyde and later transferred to 80% alcohol, a mode of treatment that precludes analysis of genetic material.
Consequently, the team’s article in the magazine plus one Ask researchers around the world to be on the lookout for the eventual discovery of similar organisms.
«We published this document in part as a cry for help,» says Dr. Olesen.
«There may be someone out there to help classify them.»