Sources:

-Encyclopedia of Life - http://eol.org
-Palaeos- http://www.palaeos.org/
-Smithsonian National Museum of Natural History - http://paleobiology.si.edu
-Penn College of Arts & Sciences - http://www.sas.upenn.edu/~rlenet/Earthworms.html
-Wikipedia - http://en.wikipedia.org

Citation: García, A.I. 2015. The Tree Of Nature (Online) at http://thetreeofnature.com

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