Acoela

Acoela is a taxonomic order of very small invertebrate animals which resemble flatworms. This order is treated either as a group within the flatworms or as one of two classes within the phylum Acoelomorpha, in which case Acoela contains the majority of that phylum`s species. Acoela comprises about 20 families. These animals have a simple nervous ....
Found on http://en.wikipedia.org/wiki/Acoela

Acoela

(from the article `flatworm`) ...endocommensal (i.e., living, respectively, outside or inside another organism without harming it), or parasitic; about 3,000 species.Order ...
Found on http://www.britannica.com/eb/a-z/a/12
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