A boy holding a horseshoe crab.
horseshoe crab definition by Webster's New World
Webster's New World College Dictionary Copyright © 2010 by Wiley Publishing, Inc., Cleveland, Ohio. Used by arrangement with John Wiley & Sons, Inc.
any of an order (Xiphosura, class Merostomata) of sea arthropods shaped like the base of a horse's foot and having a long, spinelike tail
horseshoe crab definition by American Heritage Dictionary
Any of various marine arthropods of the class Merostomata, especially Limulus polyphemus or Xiphosura polyphemus of eastern North America, having a large rounded body and a stiff pointed tail. Also called king crab, limulus.