An international team of scientists including Albert Poustka from the Max Planck Institute for Molecular Genetics in Berlin has discovered that Xenoturbellida and the acoelomorph worms, both simple marine worms, are more closely related to complex organisms like humans and sea urchins than was previously assumed. As a result they have made a major revision to the phylogenetic history of animals. Up to now, the acoelomate worms were viewed as the crucial link between simple animals like sponges and jellyfish and more complex organisms. It has now emerged that these animals did not always have as simple a structure as they do today.
With the help of extremely processor-intensive mathematical models, the scientists examined microRNAs) and a large set of several hundred genes from the genomes of Acoelomorpha and Xenoturbellida. The analysis of the Xenoturbella microRNAs and the acoelomate worm Hofstenia miamia showed that the previously analyzed acoelomate worm Symsagittifera roscoffensis had lost many of these microRNAs. The gene repertoire of the analyzed animals points instead to the kinship between these animals and the deuterostomes. For example, they have a microRNA that was previously only known to exist in echinoderms and acorn worms. Moreover, all of the animals analyzed up to now from the new Xenacoelomorpha phylum have the gene RSB66, which could previously only be demonstrated in deuterostomes.
Philippe H, Brinkmann H, Copley RR, Moroz LL, Nakano H, Poustka AJ, Wallberg A, Peterson KJ, Telford MJ. (2011) Acoelomorph flatworms are deuterostomes related to Xenoturbella. Nature 470(7333), 255-58. [abstract]
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