There are four known species of horseshoe crabs still in existence; the one that I’m familiar with is the Limulus Polyphemus. This type is found on the entire east coast of North America and in the golf
of Mexico.

These typically get up to 19″ in size and weigh in at about 3 to 5 pounds, at least the ones that I have found. There really isn’t much to these animals and even their shells do not add much to the
weight.