Invertebrate Department

The tree below shows the suggested relationship between the gnathiferan groups. Gnathifera are supported by the presence of jaws composed of densely packed rod-like structures. Furthermore, the jaw element that corresponds to the main jaw in L. maerski also appear to present in Gnathostomulida and Rotifera. Hence this feature is also a synapomorphy for Gnathifera. If we move one step up, the gnathostomulids branch of as the first group. Therefore we say that Gnathostomulida is the sister group to the rest of the gnathiferans. The sister group to Gnathostomulida, containing Micrognathozoa, Acanthocephala and Rotifera is supported by the presence of some other jaw elements that not are present in Gnathostomulida. Furthermore, they have a very specialized integument. Most other animals have an outer protective layer, a cuticle, that is secreted by the integumental cells. Such a cuticle is lacking in Micrognathozoa, Acanthocephala and Rotifera. Instead they have a web of protein fibers located inside their integumental cells. If we move up one step further we have the group containing Acanthocephala and Rotifera. Towards this group the integument has been more specialized. It still contains the above mentioned protein web, but the cell walls have been reduced so that they no longer are separated. Furthermore, the body ciliation is lost so only the head region is ciliated. As mentioned acanthocephalans are highly specialized parasites without mouth, pharynx and gut, and also their outer ciliation has been totally reduced. However, the organization of their integument is very similar to what we find in the rotifers.



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Micrognathozoa main page Reinhardt M. Kristensen Martin V. Sørensen

Last update: 04 september 2002


Responsible editor for this page: Martin V. Sørensen