[Taxacom] another putative arthropod outgroup

Ken Kinman kinman at hotmail.com
Fri Sep 28 20:47:53 CDT 2012

Dear All,      Beside tardigrades and onychophorans, another taxon (Pentastomida) has also long been put forward as an outgroup to euarthropods (or arthropods in general, including fossil taxa).  However, molecular data (18S rRNA and mitochondrial data), along with very limited morphological data, indicates that pentastomids are actually highly modified (morphologically "simplified") maxillopodan crustaceans.         
      Anyone want to weigh in on whether morphologists (especially paleontologists) or molecularists are right on this one?  The paleontological morphologists insist that it is unparsimonous to assume that pentastomids have secondarily lost so many crustacean morphologies, even though they are highly derived due to their parasitic life styles (see weblink below).  The question is whether they are right, or whether the molecularists are just sorely in need of far more molecular data on the pentastomids.  Anyway, if pentastomids are secondarily simplified crustaceans, will tardigrades turn out to also be secondarily simplified arthropods (although perhaps from another branch of arthropods such as chelicerates)?  The debate continues.                      
              ---------------------Ken Kinman                        

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