The current view is that Cycloneuralia together with the Arthropoda form the Ecdysozoa. Cycloneuralia comprises the sister taxa Nematoida (Nematomorpha + Nematoda; development of the latter is treated separately in Chap. XX) and Scalidophora (Priapulida, Kinorhyncha, Loricifera) (Fig. 1.1). The taxon Cycloneuralia has been erected based on morphological data by Ahlrichs (1995), and the main defining character is a circumpharyngeal brain that forms an equally thick ring around the foregut. The taxon Scalidophora is characterized by scalids on its introvert. The Cycloneuralia were proposed before the results of the seminal work of Aguinaldo et al. (1997) who found the first molecular evidence for the Ecdysozoa. Since then, molecular phylogenies have consistently supported the Ecdysozoa but largely fail to provide a solid support for the Cycloneuralia. One problem is that most studies do not include the Loricifera in their analyses – and those who do only receive low support for their placement at any branch within Ecdysozoa. Another issue is that in most phylogenomic studies, tardigrades group together with nematodes, which is likely an artifact that could only be eliminated in some approaches. However, studies with increased taxon sampling should help to resolve the ambiguous results in the molecular phylogenies in the near future.


Larval Stage Cleavage Pattern Postembryonic Development Median Ring Phylogenomic Study 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


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© Springer-Verlag Wien 2015

Authors and Affiliations

  1. 1.Sars International Centre for Marine Molecular BiologyUniversity of BergenBergenNorway

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