Reference

Reference 

Understanding Evolution. (N.D). The Arthropods Story, 2014. Retrieved on 14th August 2014                                 from: http://evolution.berkeley.edu/evolibrary/article/arthropodstory

UCMP. (N.D). Eurypterida , 2014. Retrieved on 14th August 2014                                                                         from: http://www.ucmp.berkeley.edu/arthropoda/chelicerata/eurypterida.html