Dendrogramma

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Dendrogramma
Dendrogramma enigmatica sp. nov., holotype.png
Dendrogramma enigmatica
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Cnidaria
Class: Hydrozoa
Order: Siphonophorae
Family: Rhodaliidae
Genus: Dendrogramma
Just, Kristensen, & Olesen, 2014 [1]
Type species
Dendrogramma enigmatica
Just, Kristensen, & Olesen, 2014
Species
  • D. enigmaticaJust, Kristensen, & Olesen, 2014 (=D. discoides)

Dendrogramma enigmatica is a species of siphonophore, the only one in its genus. It has been first described in 2014 on the basis of its morphology from a collection of specimens gathered in 1986. Its taxonomic affinity among animals was then unclear, but RNA from new specimens in 2016 allowed it to be identified as a siphonophore by barcoding and phylogenomics. The specimens are presumed to represent parts (bracts) of an entire siphonophore that has not been identified yet.

Contents

Discovery

The first Dendrogramma specimens were collected off the south-east coast of Australia during a scientific expedition in 1986. They were collected at water depths of 400 metres (1,300 ft) and 1,000 metres (3,300 ft) on the continental slope near Tasmania, [2] using a sled that was dragged over the sea floor to collect bottom-dwelling animals. [3] The researchers were immediately struck by the unusual characteristics of the 18 specimens they collected. These were preserved in formaldehyde, and later in ethanol, for further study.

On returning to the sample site in 1988, the researchers were unable to find any further specimens. It was not until 2014 that they published the discovery. [4] 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." [5]

When initially discovered, Dendrogramma's relationships were unclear. [1] The two purported species were assigned their own genus, Dendrogramma, [2] and family, Dendrogrammatidae; [6] 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." [4] The lead scientist of the identification effort, Jørgen Olesen of the University of Copenhagen, suggested that they represent "an early branch on the tree of life, with similarities to the 600 million-year-old extinct Ediacara fauna." [7] At least three genera 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] This possibility generated considerable excitement: Simon Conway Morris of the University of Cambridge stated that the discovery is "a very interesting surprise, and it poses lots and lots of questions." He noted the "most intriguing similarity to certain Ediacaran forms," but cautioned that "the similarities are exactly that. They are intriguing rather than compelling." [5] Genetic identification was not possible with the original specimens as they were preserved with formaldehyde and alcohol, a method that does not preserve nucleic acids suitably for most analyses. [2]

Consequently, in 2015, the International Institute for Species Exploration named it as one of the "Top 10 New Species" for new species discovered in 2014. [8] [9]

In late 2015, an expedition aboard the RV Investigator rediscovered the organism and collected 85 specimens in a manner that allowed genetic analysis, putting an end to the prior speculation. [10]

Naming

The genus name Dendrogramma derives from the two ancient greek words δένδρον (déndron), meaning "tree", and γράμμα (grámma), meaning "drawing, mathematical figure". [11] [12] It alludes to the branching pattern of the digestive canals, [1] which resemble dendrograms, i.e., branching diagrams frequently used by biologists to illustrate the evolutionary relationships among organisms.

The specific name enigmatica of the type species refers to the mysterious nature of the organisms, while discoides — the species epithet of the purported second species — alluded to the disc-like shape of the animals. [3]

Description

Preserved specimens of Dendrogramma. Multiple Dendrogramma.png
Preserved specimens of Dendrogramma.

The specimens first collected were roughly mushroom-shaped, and with a mostly asymmetrical structure. So far, no sex organs or nervous system have been detected. [13] The specimens consist of a flattened, somewhat circular disc and a stalk with what was originally interpreted as mouth on the end, surrounded by lobes. The "mouth" on the end of the stalk leads to what was presumed to be a digestive canal that forks repeatedly when it reaches the disc. The individuals have an outer skin, with what was taken to be a stomach separated from the skin by a layer of dense gelatinous material (mesoglea). The stalks measure up to 8 millimeters in length, while the disc ranges from 11 to 17 mm in diameter, although the original specimens experienced significant shrinkage in full-strength ethanol after measurements were made. [1]

There were originally thought to be two species, primarily differing in shape of the disc and proportional length of the stalk: D. discoides has a complete disc and proportionally shorter stalk (length about 10% of the disc diameter) while D. enigmatica has a notched disc and proportionally longer stalk (up to 70% of disc diameter). [1] The species were later shown to represent varieties of a single species. [14]

Although they are now interpreted as detached bracts (parts) of the entire siphonophore (which remains unidentified), [14] the specimens were first interpreted as free-living organisms, as they did not appear to show evidence of having been attached to something else, whether a surface or each other. [5]

Relationships

Dendrogramma has a body plan similar to animals in the phyla Cnidaria and Ctenophora, but the observed specimens lack the stinging cells that define cnidarians and the tentacles that define ctenophorans. DNA barcoding based on mitochondrial (COXI and 16S rRNA) and nuclear ribosomal (18S rRNA and 28S rRNA) markers, combined to molecular phylogenetics based on sequences from 155 nuclear genes extracted from the transcriptome, indicate a relationship with the Rhodaliidae siphonophores. [14] More specifically, Dendrogramma appears closely related to members of the families Agalmatidae ( Agalma ), Abylidae ( Abylopsis ), and Prayidae ( Craseoa ).

Related Research Articles

<i>Pteridinium</i> Ediacaran fossil

Pteridinium is an erniettomorph found in a number of Precambrian deposits worldwide. It is a member of the Ediacaran biota.

<i>Dickinsonia</i> Extinct genus of early animals

Dickinsonia is a genus of extinct organism, most likely an animal, that lived during the late Ediacaran period in what is now Australia, China, Russia, and Ukraine. It is one of the best known members of the Ediacaran biota. The individual Dickinsonia typically resembles a bilaterally symmetrical ribbed oval. Its affinities are presently unknown; its mode of growth has been considered consistent with a stem-group bilaterian affinity, though various other affinities have been proposed. It lived during the late Ediacaran. The discovery of cholesterol molecules in fossils of Dickinsonia lends support to the idea that Dickinsonia was an animal, though these results have been questioned.

<i>Cyclomedusa</i> Extinct genus of aquatic animals

Cyclomedusa is a circular fossil of the Ediacaran biota; it has a circular bump in the middle and as many as five circular growth ridges around it. Many specimens are small, but specimens in excess of 20 cm are known. The concentric disks are not necessarily circular, especially when adjacent individuals interfere with each other's growth. Many radial segment lines — somewhat pineapple-like — extend across the outer disks. A few specimens show what might be a stem extending from the center in some direction or other.

<i>Ausia fenestrata</i> Genus of marine filter feeders

Ausia fenestrata is a curious Ediacaran period fossil represented by only one specimen 5 cm long from the Nama Group, a Vendian to Cambrian group of stratigraphic sequences deposited in the Nama foreland basin in central and southern Namibia. It has similarity to Burykhia from Ediacaran (Vendian) siliciclastic sediments exposed on the Syuzma River of Arkhangelsk Oblast, northwest Russia. This fossil is of the form of an elongate bag-like sandstone cast tapering to a cone on one end. The surface of the fossil is covered with oval depressions ("windows") regularly spaced over the surface in the manner of concentric/parallel rows. The taxonomic identity of Ausia is unresolved.

<i>Kimberella</i> Primitive Mollusc-like organism

Kimberella is an extinct genus of bilaterian known only from rocks of the Ediacaran period. The slug-like organism fed by scratching the microbial surface on which it dwelt in a manner similar to the gastropods, although its affinity with this group is contentious.

<span class="mw-page-title-main">Siphonophorae</span> Order of colonial hydrozoans with differentiated zooids

Siphonophorae is an order within Hydrozoa, which is a class of marine organisms within the phylum Cnidaria. According to the World Register of Marine Species, the order contains 175 species described thus far.

<span class="mw-page-title-main">Rangeomorph</span> Form taxon of frondose Ediacaran fossils

The rangeomorphs are a form taxon of frondose Ediacaran fossils that are united by a similarity to Rangea. Some researchers, such as Pflug and Narbonne, suggest that a natural taxon Rangeomorpha may include all similar-looking fossils. Rangeomorphs appear to have had an effective reproductive strategy, based on analysis of the distribution pattern of Fractofusus misrai, which consisted of sending out a waterborne asexual propagule to a distant area, and then spreading rapidly from there, just as plants today spread by stolons or runners.

<i>Tribrachidium</i> Extinct genus of invertebrates

Tribrachidium heraldicum is a tri-radially symmetric fossil animal that lived in the late Ediacaran (Vendian) seas. In life, it was hemispherical in form. T. heraldicum is the best known member of the extinct group Trilobozoa.

<span class="mw-page-title-main">Vendobionta</span> Group of extinct creatures that were part of the Ediacaran biota

Vendobionts or Vendozoans (Vendobionta) are a proposed very high-level, extinct clade of benthic organisms that made up of the majority of the organisms that were part of the Ediacaran biota. It is a hypothetical group and at the same time, it would be the oldest of the animals that populated the Earth about 580 million years ago, in the Ediacaran period. They became extinct shortly after the so-called Cambrian explosion, with the introduction of fauna formed by more recognizable groups and more related to modern animals. It is very likely that the whole Ediacaran biota is not a monophyletic clade and not every genus placed in its subtaxa is an animal.

<i>Charniodiscus</i> Genus of extinct Ediacaran lifeform

Charniodiscus is an Ediacaran fossil that in life was probably a stationary filter feeder that lived anchored to a sandy sea bed. The organism had a holdfast, stalk and frond. The holdfast was bulbous shaped, and the stalk was flexible. The frond was segmented and had a pointed tip. There were two growth forms: one with a short stem and a wide frond, and another with a long stalk, elevating a smaller frond about 50 centimetres (20 in) above the holdfast. While the organism superficially resembles the sea pens (cnidaria), it is probably not a crown-group animal.

<i>Rangea</i> Fossil taxon

Rangea is a frond-like Ediacaran fossil with six-fold radial symmetry. It is the type genus of the rangeomorphs.

<i>Aspidella</i> Genus of Ediacaran animals

Aspidella is an Ediacaran disk-shaped fossil of uncertain affinity. It is known from the single species A. terranovica.

<i>Parvancorina</i> Genus of fossil arnimal

Parvancorina is a genus of shield-shaped bilaterally symmetrical fossil animal that lived in the late Ediacaran seafloor. It has some superficial similarities with the Cambrian trilobite-like arthropods.

<span class="mw-page-title-main">Ediacaran biota</span> Life of the Ediacaran period

The Ediacaranbiota is a taxonomic period classification that consists of all life forms that were present on Earth during the Ediacaran Period. These were enigmatic tubular and frond-shaped, mostly sessile, organisms. Trace fossils of these organisms have been found worldwide, and represent the earliest known complex multicellular organisms. The term "Ediacara biota" has received criticism from some scientists due to its alleged inconsistency, arbitrary exclusion of certain fossils, and inability to be precisely defined.

<i>Pambikalbae hasenohrae</i> Extinct genus of hydrozoans

Pambikalbae is a monospecific genus known from the Ediacaran Period of South Australia. Its morphology resembles the morphology of colonial cnidarians, such as sea pens or siphonophores.

<i>Ventogyrus</i> Extinct genus of invertebrates

Ventogyrus is an Ediacaran fossil found in the White Sea-Arkhangelsk region of Russia. It was first discovered in the Teska member of the Ust'-Pinega formation, in a thick lens of sandstone, originally sand dumped by storm waves that cut a deep channel through the shallow sea bottom where the organisms lived. Many individuals were preserved on top of each other, often torn or in distorted positions. As a result, it was originally thought to have had a "boat shaped" form and to have lived anchored in the sea floor. However, a nearby site discovered later by Mikhail Fedonkin yielded separate specimens which were beautifully preserved in an upright position and showed the internal anatomy.

<span class="mw-page-title-main">Rhodaliidae</span> Family of hydrozoans

Rhodaliidae is a family of siphonophores. In Japanese they are called ヒノマルクラゲ.

Eoporpita is a disc or ellipse-shaped Ediacaran fossil with unsure taxonomy/classification. It is known from its type species, Eoporpitamedusa, the only species within the genus Eoporpita.

Hadrynichorde is a frondose organism from the Ediacaran period discovered in Newfoundland, Canada. It is a sessile, benthic marine organism. resembling modern sea whips.

<i>Hapsidophyllas</i> Ediacaran rangeomorph fossil Hapsidophyllas flexibilis

Hapsidophyllas is a rare Ediacaran rangeomorph fossil found at Mistaken Point, Newfoundland, Canada. It was first identified by Emily Bamforth and Guy Narbonne in 2009. Its name comes from the Greek words for “a network of leaves.” Because its characteristic flexible leaflet structure is dissimilar to other known rangeomorphs, Bamforth and Narbonne describe it as a new rangeomorph form, called hapsidophyllid. The only other known hapsidophyllid is the Ediacaran frond Frondophyllas grandis, which shares the network-like configuration of leaflets seen in Hapsidophyllas. Currently, the Hapsidophyllas flexibilis holotype resides in its type locality in the Mistaken Point Ecological Reserve, and a cast of the specimen is on display at the Royal Ontario Museum in Toronto, Canada.

References

  1. 1 2 3 4 5 Just, J.; Kristensen, R.M.; 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. Bibcode:2014PLoSO...9j2976J. doi: 10.1371/journal.pone.0102976 . PMC   4153628 . PMID   25184248.
  2. 1 2 3 Rincon, Paul (3 September 2014). "Deep sea 'mushroom' may be new branch of life". BBC News. Retrieved 4 September 2014.
  3. 1 2 Skinner, Nicole (3 September 2014). "Sea creatures add branch to tree of life". Nature. doi: 10.1038/nature.2014.15833 . S2CID   87680682.
  4. 1 2 Nuwer, Rachel (3 September 2014). "Deep-Sea Mushroom Creatures Found Off Australia". Smithsonian.com. Retrieved 4 September 2014.
  5. 1 2 3 4 Frazer, Jennifer (3 September 2014). "New Deep-Sea Animal Species Look Like Mushrooms but Defy Classification". National Geographic. Archived from the original on September 4, 2014. Retrieved 4 September 2014.
  6. ↑ John Timmer (9 September 2014). "Tasmanian depths may have been hiding unknown animal phylum". Ars Technica.
  7. ↑ "Two unclassifiable species found off Australian coast". Press Association. 4 September 2014. Retrieved 4 September 2014.
  8. ↑ "The ESF Top 10 New Species for 2015". State University of New York College of Environmental Science and Forestry. Archived from the original on 18 August 2021. Retrieved 13 November 2015.
  9. ↑ Berenson, Tessa (21 May 2015). "These Are the Top 10 New Species Discovered Last Year". Time. Retrieved 13 November 2015.
  10. ↑ Gough, Myles (7 June 2016). "Origin of mystery deep-sea mushroom revealed". BBC News. Retrieved 7 June 2016.
  11. ↑ Bailly, Anatole (1981-01-01). Abrégé du dictionnaire grec français. Paris: Hachette. ISBN   978-2010035289. OCLC   461974285.
  12. ↑ Bailly, Anatole. "Greek-french dictionary online". www.tabularium.be. Retrieved October 21, 2018.
  13. ↑ Coghlan, Andy (5 September 2014). "Weird creatures may be relics from dawn of animal life". New Scientist. Retrieved 2018-10-21.
  14. 1 2 3 O’Hara, Timothy D.; Hugall, Andrew F.; MacIntosh, Hugh; Naughton, Kate M.; Williams, Alan; Moussalli, Adnan (June 2016). "Dendrogramma is a siphonophore". Current Biology. 26 (11): R457–R458. doi: 10.1016/j.cub.2016.04.051 . PMID   27269719.
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