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Old 10/24/2005, 11:01 AM
rshimek rshimek is offline
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Join Date: Oct 1999
Posts: 24,898
Hi Brian,

Yup, as Mike has pointed out it is a polyclad flatworm.

To clear up some confusion... the old taxonomic grouping called the "Phylum Platyhelminthes" is no longer considered to be a valid group. Examination of the fine structure of the animals in it, coupled with analyses of the genetic material, indicates that it was a "false" grouping, one made on gross structural appearance. Unfortunately, not all things that look alike are related (sorta like sharks, porpoises, and tuna all have the same general shape, but are only very distantly related).

The so-called "red planaria" not only are not planarians, but now are recognized as being members of an entirely separate group, given the name the Acoela or Acoelomorpha. Planarians - and polyclads such as the animal illustrated in the first post of this thread - are in the group that used to be called the "Class Turbellaria" of the Phylum Platyhelminthes. Calling them "Turbellarians" (a group now including actual planarians, polyclads, and several other meaty free-living (mostly) flatworms) is probably the best way to go. I suspect the nomenclature of the group will shake out over the next few years as more work is done on the internal inter-relationships within it.