[Taxacom] The importance of Phylum Tardigrada

[Kenneth Kinman]

Dear All,                     Dunn et al. 2009 showed that within Ecdysozoa, Phylum Tardigrada is phylogenetically more closely related to Cycloneuralia than it is to Panarthropoda.  And in particular, tardigrades are very closely related to nematodes (which have simply lost characters such as segmentation and legs).  More importantly, it seems to me that Panarthopoda is probably paraphyletic, giving rise to Cycloneuralia through a tardigrade-type intermediate.             The only question will be whether tardigrades and onychophorans evolved independently from bivalved crustaceans, or if a single group of bivalved crustaceans gave rise to a common ancestor of onychophorans and tardigrades (and through the latter to cycloneuralians).  Either way, the phylogeny of Ecdysozoa could be soon understood if we embrace the probability of de-arthropodization and bivalve-loss as major factors in the evolution of cycloneuraliam animal phyla.   
         And then it should become readily apparently that Lophotrochozoa is not a clade at all, but a relatively useless paraphyletic assemblage in need of phylogenetic splitting.  I've never understood the notion that Lophotrochozoa is a clade.  Once that notion is finally debunked, we can actually begin to understand the phylogeny of Kingdom Metazoa.   Dunn et al., 2009, was just a first step in improving the "resolution of the animal tree of life."
Dunn, CW; Hejnol, A; Matus, DQ; Pang, K; Browne, WE; Smith, SA; Seaver, E; Rouse, GW; et al. (2008). "Broad phylogenomic sampling improves resolution of the animal tree of life". Nature 452 (7188): 745–749.