How many times have you walked the beaches of Hilton Head Island and seen a horseshoe crab on the sand? Large and dark, with long pointed tails, multiple legs and flat “book” gills on their underside, they are commonly seen on our beaches, both alive and as skeletons. They are from a very ancient time, and look more like a Frankenstein experiment gone wrong than a modern-day crab; but then, they are not really crabs.
Horseshoe crabs actually are most closely related to spiders, scorpions, ticks and mites, and their ancestors have existed on earth from a time before the dinosaurs, a time when the first fish with jaws appeared in the oceans and glacial melting brought about a significant rise in sea level.