Friday, 5 September 2014

Strange Deep Sea Mushroom-Shaped Animals Discovered

Several views of Dendrogramma enigmatica
Photos of the newly discovered, mushroom-shaped
Dendrogramma enigmatica
In a paper that appeared this week on PlosOne, researchers from the University of Copenhagen announced the discovery of two new strange, deep sea and mushroom-shaped animals. The two species were identified from a collection of specimens that were collected back in 1986.

The authors assigned the newly described Dendrogramma enigmatica and Dendrogramma discoides under the animal kingdom, however they couldn't classify them into an existing phylum. A new family, Dendrogrammatidae, was established for the species.

Discovery, History & Naming
In a 1986 scientific expedition, the authors collected numerous specimens of several organisms at 400 and 1000 m (~1,300 ft - 3,300 ft) deep, off the south-east coast of Australia, on the continental slope near Tasmania.

The scientists were immediately shocked by the unusual Dendrogramma specimens (18 in total) they had collected and preserved them in formaldehyde and later ethanol for further examination. They returned to the same site two years later, but failed to recover further specimens.

But why did it take them almost thirty years to publish the discovery? Jean Just, from the University of Copenhagen, who carried out the trawling in 1986 explains:

"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 have really stumbled across something special." [2]

Dendrogramma is a reference to dendrograms, a type of tree diagram used in biology to illustrate evolutionary relationships between organisms. As for the species specific names, they are a reference to their mysterious character (enigmatica) and disc shape (Greek: disco+ides), respectively.

Dendrogramma discoides from several angles
Dendrogramma discoides
A. adoral view B. enlarged part of disc
C. aboral view D.oblique adoral view.
(click image to enlarge)

Both species are multicellular and mostly non-symmetrical, with a dense layer of gelatinous material between the outer skin cell and inner stomach cell layers. They are relatively small, less than an inch long (2.5 cm) when alive and roughly mushroom-shaped.

The body consists of a flattened disc and a stalk with a mouth on the end, surrounded by lobes. The mouth leads to a digestive canal that forks repeatedly when it reaches the disc. The mouth is small and simple and how they feed is unclear. However, it has been suggested that the mucus secreted by the lobes around the mouth may be used for capturing microorganisms in the water.

"With their small, simple mouth opening it would seem likely that they feed on micro-organisms, perhaps trapped by mucus from the specialized lobes surrounding the mouth opening.", extract from the study.

These strange animals appear to be free-floating as they appear to lack a means of propulsion and are probably incapable of swimming. Furthermore, they do not show evidence of having been attached to something else, whether a surface or each other.

Dendrogramma enigmatica body anatomy
Dendrogramma enigmatica
A. holotype, ‘lateral’ view  B. same, aboral view.
C. cross-section through approx. half of stalk
(click image to enlarge)

Biological classification
The two animals have a body that bears certain similarities with species from the phyla Cnidaria and Ctenophora, however the authors say that they lack key anatomical features that are unique to either of these groups. Some of these features include cnidocytes, tentacles, marginal pore openings for the radiating canals, ring canal, sense organs and other structures mentioned in the paper.

"Dendrogramma shares a number of similarities in general body organisation with the two phyla, Ctenophora and Cnidaria, but cannot be placed inside any of these as they are rrecognizedcurrently.", extract from the study.

The researchers assigned the two species in their own genus, but refrained from erecting a new phylum, as new material is needed to resolve many pertinent outstanding questions. For now, Dendrogramma is referred to incertae sedis [something like unknown phylum]. For this reason, the authors recommend "that attempts be made to secure new material for further study".

"We published this paper in part as a cry for help. There might be somebody out there who can help place it." said co-author Jorgen Olesen, from the University of Copenhagen. [4]

Unfortunately, genetic identification which could help in the classification is impossible, as all specimens were preserved with formaldehyde and alcohol, a method that destroys genetic material.

Scientific Importance
The discovery of a new species is always welcome, but not always of great scientific importance. However, this isn't probably the case with the Dendrogramma species, especially if they lead to the establishment of a new phylum. Some have even said that textbooks in zoology may need to be rewritten!

Leonid Moroz, a neurobiologist at the University of Florida's Whitney Laboratory for Marine Bioscience in St. Augustine, said that if the new species proves to be descendants of early animals [scroll down for more info], 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." [3]

Let's see what some other experts had to say:
"It would be incredibly exciting if the authors have found a previously unknown group of animals that diverged from other animals so early." said Casey Dunn, an evolutionary biologist at Brown University in Providence, Rhode Island. [2]
"This discovery implies an exciting possibility that the deep-sea of Australia has preserved living descendants of the Ediacara organisms, which were thought to be extinct over 500 million years ago." said Tetyana Nosenko, an evolutionary biologist at Ludwig Maximilian University in Munich, Germany. [2]

Ediacaran Descendants
The two Dendrogramma species bear a striking resemblance to certain Ediacaran forms, like Albumares, Anfesta, and Rugoconites. These life-forms have long gone extinct, more than 500 million years ago at the end of the Ediacaran period and are only known from the fossil record.

Although unlikely, there is a chance that Dendrogramma are Ediacaran descendants, making them the first animals to survive to modern times in their original form.

"If this is true, then we have discovered animals which we'd expect to be extinct around 500 million years ago.", said study co-author Reinhardt Kristensen, an invertebrate zoologist at the University of Copenhagen, 

- The research was supported by an Australian Marine Science and Technology/Australian Research Council grant. The funder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
- All photos in this article are licensed under the Creative Commons Attribution (CC BY) license. Please include the first reference to Plos One if you wish to redistribute, remix etc. Click here for more info.

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) PMID: 25184248
- Rincon, Paul. "Deep sea 'mushroom' may be new branch of life"
- Skinner, Nicole. "Sea creatures add branch to tree of life"
- Rincon, Paul. "Deep sea 'mushroom' may be new branch of life"

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