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EvolutionEvolution

Curious Sea Creatures May Add Entirely New Branch to the Tree of Life

ByTim De ChantNOVA NextNOVA Next

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Finding a new species is usually enough to merit a mention in the news. But uncovering an entirely new phylum—the taxonomic level just below kingdom—well, that’s another thing entirely.

Three Danish scientists may have discovered just that when they were examining old specimens collected during a 1986 expedition off the coast of Tasmania. One group stood out in particular, a group that had been overlooked back when the samples were originally pulled from the deep. The critters look like somewhat like a jellyfish and somewhat like a tiny mushroom (they are only about a half inch across). Back when the specimens were collected, they had been fixed in formaldehyde and then stored in alcohol, which destroyed most of the DNA. So the team worked to classify the mysterious organisms the old fashioned way, by studying their features.

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Like jellyfish, the critters, which the team call Dendrogramma , have a common opening through which they eat food and expel waste. Nutrients get to where they’re needed through a branching “gastrovascular” system, a sort of hybrid stomach and circulatory system. The animals are circular, like jellyfish, but have a notch on one side, suggesting that Dendrogramma may not be radially symmetric. Radial symmetry is a hallmark of the cnidarians, or jellyfish, which told the researchers these probably didn’t belong in that phylum. The scientists also considered grouping the puzzling animals with comb jellies, but the specimens lacked features that would have tied them to that phylum, too.

John Timmer, writing for Ars Technica:

As a result, the authors assign the two species their own family, Dendrogrammatidae [sic], after the branching patter of the gastrovascular system. But this was a case where the peer reviewers (who often ask authors to tone down dramatic claims) thought they were being too cautious: “It has been suggested during review that Dendrogramma could represent a new non-bilaterian phylum. While we may agree, we refrain from erecting such a high-level taxon for the time being.” (A phylum is the second highest level grouping of species, just below kingdom.)

Without genetic evidence to fill out the picture, I can see how the authors were hesitant to pump up their claims from finding a new family to discovering an entirely new phylum. Settling the matter will undoubtedly require new samples, ideally with their DNA in tact. Other scientists have resampled the seas off Tasmania looking for more Dendrogramma , but the mushroom-shaped creatures have remained elusive for the last 30 years.

While not as significant a discovery as an entirely new kingdom, new phyla are rare. If these organisms constitute a new phylum rather than just a family, then that suggests new branches on the evolutionary family tree. And given the similarities the Dendrogramma specimens appear to have to some truly ancient fossils, then this new limbs may have split off very early on.