Cast from a real horseshoe crab molt, this foam replica can be cast up in a variety of colors, just like my other costume pieces. I'm only going to list the colors of thick foam (like the white foam pictured above), but if you want a wilder color (like the brown pictured above, or neon pink or something) I can also use the thinner foams; the result just won't be as sturdy. I made this because someone requested a Cthulhu themed mask that could be used to outfit a whole cult, and this horseshoe crab is wide enough (8" across on the flat) to fit around a face. It also makes pretty cool shoulder armor when done up in black. I am even told that one of them has been used to make a sea-themed fascinator. Maybe you'll come up with a use I haven't thought of yet? And this way you get to have a horseshoe crab that isn't brittle, or sea-smelling.
Bonus, I just added some pictures of a radio controlled horseshoe crab I threw together for Halloween. I'll make sure to take it with me next time I go to the beach.

To save on shipping, it will come shipped to you in three pieces, but they glue together nicely with a spot of hot glue. Also, let me know how much you want the side spines cut out. You can see them cut out individually in the white example, or just cut around in the brown. Whatever works for you, just let me know.