Dried Molted Atlantic Horseshoe Crab for Sale, measuring between 7 and 8-7/8 inches long from the edge of the head to the tip of the tail.  They may have some sand inside them. You will receive horseshoe crabs that look similar to those pictured. 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.