Xenacoelomorpha – a new phylum in the animal kingdom

Max-Planck-Gesellschaft ^ | February 15, 2011 | Unknown

[decimon]

Scientists reorganise the animal phylogenetic tree

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.

The genus Xenoturbella lives off the coast of Scandinavia, Scotland and Iceland. It shares a simple body structure with the acoelomorph worms: these organisms, which reach a maximum size of just a few millimetres, have no through gut, no gill slits and no body cavity (Greek: coelom = cavity). Many members of both groups live on the ocean floor and feed on organic particles in the sediment. Some species live parasitic, e.g. in the intestines of sea cucumbers.

The animal kingdom is divided into different evolutionary lines. These include, among others, the protostomes (“mouth first”) and deuterostomes (“second mouth”). In the protostomes, the mouth that develops at the beginning of embryonic development becomes the organism’s actual mouth, whereas, in the deuterostomes, it becomes the anus and the mouth develops at a later stage. Three deuterostome phyla were known up to now: the Chordates (e.g. vertebrates), the Echinoderms (sea urchins, starfish, sea cucumbers) and the Hemichordates (e.g. acorn worm). “Our research shows that Xenoturbellida and Acoelomorpha together form the fourth phylum which we have called ‘Xenacoelomorpha’,” explains Albert Poustka from the Planck Institute for Molecular Genetics in Berlin.

[pabianice]

What about the other new phyllum? Humans without a backbone (also called Rinos rectumus majoriatea.

[SunkenCiv]

Thanks AdmSmith.