Horseshoe Crabs - they're kind of cute, aren't they?  It's best to find them dead on the beach or in an artificial form - especially because their blood contains amebocytes, which play a role similar to white blood cells, and medical firms  harvest them, bleed them for their "blue blood" and 
then return them to the sea. Plus, they're important to the ocean ecosystem.
 (Design above by Marika Meyer)

Design by Laura Garcia, Lonny March/April 2012, photography by Patrick Cline

Bronze Limule Sconce, here

Painted silver, from etsy here