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Horseshoe Crab: History and Biology
Resource is filled with lots of information presented in an easy to follow format. Illustrations are excellent.
Regents of the University of Michigan
Animal Diversity Web: Class Merostomata (Horseshoe Crab)
Find general information about the Merostomata class, which includes horseshoe crabs and the extinct eurypterids. Topics include diet, body charactersitics, and respiratory system.