Neither jellyfish nor comb jelly.
Scientists have identified two mushroom-shaped marine animals that do not fit in any of the known categories of the tree of life and could be related to groups thought to be extinct for 500 million years.
Jean Just, a zoologist at the Natural History Museum of Denmark in Copenhagen, discovered 18 odd-looking invertebrate specimens while sorting through materials he had collected in the Tasman Sea in 1986. On that expedition, he was exploring the continental slope off the southeastern coast of Australia using a sled that drags over the bottom of the ocean floor and collects animals that live there.
In the study, which appears in PLOS ONE1, the researchers report 14 specimens, collected at depths of 400 and 1,000 metres, that could not be classified into any major groups, or phyla. These “little, funny, mushroom-shaped animals,” as Just calls them, are multicellular, mostly asymmetrical — a crucial characteristic for classifying organisms — and have a gelatinous layer between the inner and the outer body. More.
Here’s the abstract:
A new genus, Dendrogramma, with two new species of multicellular, non-bilaterian, mesogleal animals with some bilateral aspects, D. enigmatica and D. discoides, are described from the south-east Australian bathyal (400 and 1000 metres depth). A new family, Dendrogrammatidae, is established for Dendrogramma. These mushroom-shaped organisms cannot be referred to either of the two phyla Ctenophora or Cnidaria at present, because they lack any specialised characters of these taxa. Resolving the phylogenetic position of Dendrogramma depends much on how the basal metazoan lineages (Ctenophora, Porifera, Placozoa, Cnidaria, and Bilateria) are related to each other, a question still under debate. At least Dendrogramma must have branched off before Bilateria and is possibly related to Ctenophora and/or Cnidaria. Dendrogramma, therefore, is referred to Metazoa incertae sedis. The specimens were fixed in neutral formaldehyde and stored in 80% ethanol and are not suitable for molecular analysis. We recommend, therefore, that attempts be made to secure new material for further study. Finally similarities between Dendrogramma and a group of Ediacaran (Vendian) medusoids are discussed.
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