Xenacoelomorpha

Neochildia fusca, a representative of the Acoelomorpha

The Xenacoelomorpha are one only in 2011 described strain worm -like animals from the group of new mouths ( deuterostomes ). It consists of two strains, the Acoelomorpha about 370 species and consisting only of two types Xenoturbellida. Both sub- tribes had originally himself the rank of strains.

Features

The types of Xenacoelomorpha be a maximum of a few millimeters in size, have no consistent bowel, no anus ( the mouth also serves as an excretory organ ), no gill arches and no coelom ( body cavity ). They live in the sea, between the particles of sediment, plankton, on the surface of algae or coral or in the gut of sea cucumbers, where they feed mostly of organic particles and develop directly without a larval stage.

System

The Acoelomorpha were counted initially to the class of flatworms ( Turbellaria ) and thus belong to the phylum flatworms ( Platyhelminthes ), placed at the base of the Bilateria later. The Xenoturbellida were assigned to the Turbellaria after their discovery and first description. Later it was recognized similarities with the molluscs ( Mollusca ), and since 2003 they are placed in the new mouths.

Studies of microRNA amino acids of the fully sequenced mitochondrial DNA of some species, as well as of several hundred genes showed a relationship between these animals with each other and with the deuterostomes. Thus, the gene RSB66 was detected, which previously could only be found in deuterostomes. The microRNA of Xenacoelomorpha is so far known only from echinoderms and acorn worms, two taxa of the deuterostomes. The Xenacoelomorpha have in the course of evolution simplifies their plan and lost many of the characteristic features of deuterostomes.

The systematic position of the Xenacoelomorpha shows the following cladogram:

Xenacoelomorpha

Gill hole Animals ( Hemichrodata )

Echinoderms ( Echinodermata )

Chordates ( Chordata )