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Dendrogramma ist eine taxonomische Gattung, bestehend aus den zwei Arten Dendrogramma enigmatica und Dendrogramma discoides, welche im Jahr 2014 aus einer Sammlung von Proben im Jahr 1986 entdeckt wurden. Die beiden Arten werden im Tierreich verortet, aber noch nicht endgültig zu einem bestehenden Stamm zugeordnet.
Discovery
The Dendrogramma specimens were discovered off the south-east coast of Australia during a scientific expedition in 1986. They were collected at water depths of Vorlage:Convert and Vorlage:Convert on the continental slope near Tasmania,[1] using a sled that was dragged over the sea floor to collect bottom-dwelling animals.[2] The researchers were immediately struck by the unusual characteristics of the 18 specimens they collected and preserved them in formaldehyde and later ethanol for further study. On returning to the sample site in 1988, they were unable to find any further specimens. It was not until 2014 that they were able to write up and publish the discovery in an article published in the journal PLOS One.[3] Jean Just of the University of Copenhagen, who carried out the trawling in 1986, has explained the long delay before publication in terms of the extraordinary nature of the discovery: "Once you think you have something really extraordinary, it takes a long time to study, read, consult left, right and centre, and convince yourself that you’ve really stumbled across something special."[3]
Naming
The genus name of Dendrogramma alludes to the dendrogram, a type of tree diagram frequently used by biologists to illustrate the evolutionary relationships between organisms. One species name, enigmatica, refers to the mysterious nature of the organisms, while the other, discoides, alludes to the disc-like shape of the animal.[2]
Description
The marine organisms are a few millimeters in length, roughly mushroom-shaped, and, with a mostly non-symmetrical structure, do not belong to the bilateria. They consist of a flattened disc, and a stalk with a mouth on the end, surrounded by lobes. The mouth on the end of the stalk leads to a digestive canal that forks repeatedly when it reaches the disc. They have an outer skin, with a stomach separated from the skin by a layer of dense gelatinous material.[4]
The animals appear to be free-living, as they do not show evidence of having been attached to something else, whether a surface or each other. There is no obvious sign that they have a means of propulsion and they do not appear to be capable of swimming. Their mouths are small and simple and their manner of feeding is unclear; however, it has been suggested that the lobes around the creatures' mouths secrete a mucus which is used to capture microbes in the water.[5]
Relationships
Species of Dendrogramma have a similar body plan to animals in the phyla Cnidaria and Ctenophora, but lack certain anatomical features unique to either of these groups. The relationship between Cnidaria, Ctenophora, and other basal metazoa is not firmly resolved. Dendrogramma is a basal metazoan, but the sister group to these organisms is unclear.[4] They have been assigned their own genus[1] and the researchers even considered putting them in their own phylum. As they put it, however, "we refrain from erecting such a high-level taxon for the time being, because new material is needed to resolve many pertinent outstanding questions."[3]
The University of Copenhagen's Jørgen Oleson, the lead scientist of the identification effort, suggests that they represent "an early branch on the tree of life, with similarities to the 600 million-year-old extinct Ediacara fauna."[6] At least three species of Ediacarans, Albumares, Anfesta, and Rugoconites share similarities with Dendrogramma; all three appear to have possessed a disc with an internal network of forking channels.[5]
Genetic identification, which could help place the organisms on the tree of life, cannot yet be done, as the organisms were preserved with formaldehyde and alcohol, a method which does not preserve genetic material. Further genetic research may have to wait until fresh specimens of the organisms can be obtained.[1]
Reactions
Neurobiologist Leonid Moroz, of the Whitney Laboratory for Marine Bioscience at the University of Florida, said that if the new genus turns out to be directly descended from early animals, it could "completely reshape the tree of life, and even our understanding of how animals evolved, how neurosystems evolved, how different tissues evolved."[5] Simon Conway Morris of the University of Cambridge calls the discovery "a very interesting surprise, and it poses lots and lots of questions." He notes the "most intriguing similarity to certain Ediacaran forms," but cautions that "the similarities are exactly that. They are intriguing rather than compelling."[5] Nonetheless, if it is confirmed that Dendrogramma is a descendant of the Ediacarans, Reinhardt Kristensen of University of Copenhagen comments that then "we have discovered animals which we'd expect to be extinct around 500 million years ago."[5]
The discovery of potentially an entirely new phylum is an extremely rare event; as Jørgen Olesen notes, "it's maybe only happened about four times in the last 100 years."[1] Andreas Hejnol of the Sars International Centre for Marine Molecular Biology in Bergen, Norway describes tracking down a new lineage as being "like the discovery of a treasure," as survivors of lineages thought long extinct can help researchers to reconstruct evolutionary history.[2]
==References==
{{reflist}}
[[Category:Marine animals]]
[[Category:Animal genera]]
[[Category:Animals described in 2014]]
- ↑ a b c d Paul Rincon: Deep sea 'mushroom' may be new branch of life. 3. September 2014. Abgerufen am 4. September 2014.
- ↑ a b c Nicole Skinner: Sea creatures add branch to tree of life. 3. September 2014. Abgerufen am 4. September 2014.
- ↑ a b c Rachel Nuwer: Deep-Sea Mushroom Creatures Found Off Australia, Smithsonian.com. 3. September 2014. Abgerufen am 4. September 2014.
- ↑ a b J. Just, R.M. Kristensen, J. Olesen: 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.. In: PLoS ONE. 9, Nr. 9, 2014. doi:10.1371/journal.pone.0102976. Abgerufen am 3. September 2014.
- ↑ a b c d e Jennifer Frazer: New Deep-Sea Animal Species Look Like Mushrooms but Defy Classification, National Geographic. 3. September 2014. Abgerufen am 4. September 2014.
- ↑ Two unclassifiable species found off Australian coast, Press Association. 4. September 2014.
