Palæos:		Invertebrates
METAZOA		Ecdysozoa

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Ecdysozoa

Bugs > Slugs

 

Bilateria |--Deuterostomia `--Protostomia |--Ecdysozoa | |--Bryozoa? | `--+--Tardigrada | `--Arthropoda `--Lophotrochozoa

The Ecdysozoa, for our purposes, are trated as bugs > slugs -- a stem group leading to the Arthropoda.  However, they are better known as the "molting clade" -- the animal phyla with a cuticle which is molted.  There is still considerable suspicion that they might not be a clade.  However, the validity of the Ecdysozoa is coming increasingly to be accepted among workers in this field.  Phyla included are the Arthropoda, Tardigrada, Onychophora (which together make up the "Panarthropoda"), and possibly more primitive worm-like and "pseudocoelomate" groups like the Nematoda,  Nematomorpha, Priapula, Kinorhyncha and Loricifera.  We treat these groups as Bilateria basal to the bug/slug divergence.  However, the variability of definitions and uncertainty of the data in this region of phylospace make almost any assignment possible.  

Phylogeny after Aguinaldo et. al. 1997

<==o ECDYSOZOA
      |?- Chaetognatha
      |--+-- Kinorhyncha [Kinorhynchida]
      |  `-- Priapulida
      `--+-- Nematomorpha
         |-- Lobopoda [Onychophora sensu lato] (lobopods, velvet worms)
         |-- Nemata [Nematoda] 
         |-- Tardigrada (water bears)
         |-- Crustaceomorpha
         |-- Insecta [Hexapoda] (insects)
         `--+-- Myriapoda
            `-- Chelicerata (= Arachnomorpha)

Arthropodomorpha after Conway Morris, 1993

<==o ARTHROPODOMORPHA
       |-- Cephalorhyncha
       |--+--+-- †Protoconodonta
       |  |  `-- Chaetognatha
       |  `--+-- Nematomorpha
       |     `-- Nemata [Nematoda] 
       `--+--o †Sprigginida
          |  |?- †Bomakellia
          |  `-- †Spriggina floundersi
          |?- Tardigrada (water bears)
          `-- Arthropoda (arthropods) [polyphyletic???]

Ecdysozoa After Peterson & Eernisse (2001)

Parsimony analysis of 18s rDNA

Combined parsimony analysis of morphology and 18s rDNA

cladograms by Peterson and Eernisee, showing the relationship of the various Ecdysozoa subclades.

Links

Links

Introduction to the Ecdysozoa

The Ecdysozoa: true taxon or molecular mirage? Brian K. Penney - raises some important points

The phylogenetic position of the Arthropoda Schmidt-Rhaesa, A., Ehlers, U. Bartolomaeus, T, Lemburg, C. and Garey, J.R. (1998)

Ecdysozoa photos