When we minimize LBA we find consistent support for a position of both acoelomorphs and Xenoturbella within the deuterostomes. The most likely phylogeny. Xenoturbellida and Acoelomorpha are marine worms with contentious ancestry. Both were originally associated with the flatworms. 筑波大学の研究情報ポータル、COmmunity of Tsukuba Researchers、略して COTREにようこそ!このサイトでは、筑波大学に所属する研究者の情報、筑波大学が 誇る高.

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Green worms Symsagittifera roscoffensis Graff, Photograph by Vincent Maran.

Those little guys are small worms, usually measuring less than 1 mm in length and living in marine or brackish waters or as symbionts. There are two groups of acoelomorphs: Acoels are the simplest ones; they have a mouth, but lack a gut, so that the deuterostomees ingested goes directly to the internal tissues.

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In Nemertodermatida, there is a blind gut, i. In fact, they were initially classified as flatworms, flatqorms several features later challenged their position inside this phylum. The main differences are:. Distribution of nerve chords in Acoelomorpha, Protostomia and Deuterostomia. Picture by myself, Piter K. Analyzing such features, it seems obvious that Acoelomorpha is a basal group of bilateral animals and may be the reminiscent of a primitive group of animals later almost completely extinct by their most complex descendants, the true protostomes and deuterostomes.

The original radially-distributed nerve cords were simplified in dorsal or ventral ones in higher groups, deuteerostomes remained radial in Acoelomorpha.

Several phylogenetic studies indicate that Acoelomorpha is indeed a basal group of bilateral animals. Another group of simple animals, the Xenoturubellida, was sometimes proposed as a sister group for Acoelomorpha.


Their proximity would be explained by several shared features, mainly the simple nervous system, the lack of a stomatogastric mouth-gut deutfrostomes, the structure of the epidermal cilia and the unusual fact that, in both groups, epidermal degenerated cells as resorbed in the gastrodermis. Photograph extracted from bioenv. The group Xenoturbellida, however, has been placed in Deuterostomia in some molecular studies and recently Philippe et al.

But how ate such a thing be possible when they obviously have primitive and unique features, like the radially placed nerve cords? But wait a minute! It means that that microRNA sequence is found in deuterostomes, but not in protostomes.

Now think with me. We have 4 bilateral groups here: Acoelomorpha, Xenoturbellida, Deuterostomiaa and Protostomia. The truth is that this sequence is absent in Protostomia, but present in all other groups. If you consider Xenoturbellida and Acoelomorpha inside Deuterostomia, you have to assume that they passed through a huge simplification, and you maintain the radial nerve cords unexplained.

Now if you think of them as primitive groups, the only thing necessary is to analyze protostomes as having lost a microRNA sequence. Phylogenetic position of Acoelomorpha and Xenoturbellida according to Philippe et al.

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Phylogenetic position of Acoelomorpha and Xenoturbellida according to Boll et al. Platyhelminthes ou apenas semelhantes a Platyhelminthes?

To Be or Not to Be a Flatworm: Assessing the root of bilaterian animals with scalable phylogenomic methods. Proceedings of the Royal Society B: Biological Sciences,DOI: Tracking the origins of the bilaterian patterning system: The phylogenetic position of Acoela as revealed by the complete mitochondrial genome of Symsagittifera roscoffensis.

Acoelomorph flatworms are deuterostomes related to Xenoturbella. Nature, exnoturbella, DOI: Filed under EvolutionMolecular BiologyZoology. Really interesting post; flatworms are really remarkable.


I do research on planarians from the perspective of Pharmacology and neurobiology. I am following your blog. Keep up the food work! I wanted to share with you that several colleagues and I are thinking about organizing a meeting relatd planarians, mainly from the perspective of their use in pharmacology and toxicology.

I am putting together a mailing list of interested people and I was wondering if you or any of your colleagues would be interested. Most of us work on aquatic planarians, but I think that the terrestrial ones are equally fascinating.

Xenoturbella, a growing group of weirdoes Earthling Nature. You are commenting using your WordPress. You are commenting using your Twitter account.

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Acoelomorph flatworms are deuterostomes related to Xenoturbella – UCL Discovery

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