Horseshoe Crab - Limulus polyphemus

Horseshoe Crabs are a living fossil, and they certainly look the part! Fossil Horseshoe Crabs that look nearly identical to modern specimens have been dated to roughly 450 million years ago, millions of years before even the first dinosaur. Horseshoe Crabs aren't true crabs, but are more closely related to modern arachnids such as spiders and scorpions. Their tops are well armored, and are covered with spikes, punctuated by a dangerous looking but harmless tail called a 'telson,' which they use to right themselves when flipped on their backs. Despite their prehistoric and intimidating look, Horseshoe Crabs are completely harmless to humans, and are often featured in touch tank displays at public aquariums.               

Care

Horseshoe Crabs grow to 2' long when fully grown, and require a sandbed deep enough to at least partially bury themselves in. Obviously, this necessitates a truly LARGE aquarium with plenty of open space in the sand to move around in. They are generally safe with coral, but will consume sessile invertebrates and small fish. As with other invertebrates, they're intolerant of copper and rapid changes in water conditions, so should be acclimated carefully.     

Diet

Horseshoe Crabs are carnivorous, and should be offered a diet rich in meaty frozen foods.