Two Dried Real Molted Atlantic Horseshoe Crabs for Sale (Review Photos).  One  measures approximately 9-7/8 inches long and 5-3/8 inches wide. The other molted Atlantic Horseshoe Crab measures 10-3/4 inches to the tip of its tail and 4-7/8 inches wide.  (There will be some sand inside the crabs)  They are also known as the American horseshoe crab. Scientific name: Limulus polyphemus and can be found on the American Atlantic coast and in the Gulf of Mexico.  A horseshoe crab is built like a tank! Its heavily-armored exterior protects the vulnerable parts inside. Despite their name, horseshoe crabs, are not crabs but are members of the order Xiphosura and are more closely related to  scorpions, spiders and ticks, than they are to true crabs. For the horseshoe to grow larger, it must molt and shed its shell. These "molts" can sometimes be found near tidal flats. After its third or fourth year it sheds its skin annually, sometime during July or August.