Genus doesn’t belong in any known phylum.
The discovery of 14 frail, gelatinous animals announced last week may dramatically broaden scientific understanding of animal life. The specimens can’t be placed into any known phylum, the highest division in the Animal Kingdom, but their basic body plan suggests they may belong to animal groups thought to be extinct for hundreds of millions of years.
The discovery of new species is regular in deep-sea science, but it is very rare to discover an animal that doesn’t fit anywhere in the tree of life. The study’s authors cite only three comparable examples in the last twenty years.
The animals were placed in a new genus, named Dendrogramma after the dendrogram trees biologists use to visualize the relationships between groups of life. They lack bilateralism, a body plan symmetrically reflected on two sides, possibly linking them to Cnidarians or Ctenophores – phyla that include jellyfish, corals, anemones, and comb-jellies. Dendrogramma clearly displays some form of symmetry, so they must be placed be above the Porifera phylum, which includes the sponges, commonly considered to be the most basal animal group.
Dendrogramma most closely resemble Cnidarians and Ctenophores among living animal groups, but significant differences in body plan and morphology to these phyla make inclusion unlikely. Dendrogramma may belong to the Medusoids, a primitve fossil group from the Ediacarian biota, an assemblage of primitive fossil specimens that lived from 600- to 541-million years ago. The Medusoids bear a striking resemblance to the disk portion of Dendrogramma’s body. The study’s authors suggest that Dendrogramma may in fact be living Medusoids, and that the group has been alive since the Ediacarian era. As nearly all modern animal phyla are thought to have their origins in the Cambrian Explosion that occurred after the Ediacarian era, this would affect current thinking on evolutionary history.
Scientists from the Natural History Museum of Denmark published Dendrogramma’s discovery in the journal PLOS One. A large-scale deep-sea study originally collected the specimens with a benthic sled that collected animals living in ocean sediments in 1984. The animals came from the floor of the Tasman Sea. According to Jean Just, one of the study’s authors, Dendrogramma’s significance was recognized upon its discovery, but the publication of the discovery was delayed due to its profound implications to animal diversity. The authors unsuccessfully attempted to find more specimens in 1988.
Upon discovery, the Dendrogramma specimens were stored in formaldehyde, which rendered them unsuitable for genetic testing. Every animal’s genes determine which phyla it belongs, which can sometimes be used to classify animals that can’t be visual identification. The priority is now connecting Dendrogramma to the rest of the animal kingdom, requiring live specimens that can be tested genetically.
