They are marine arthropods whose alien-looking ancestors date back hundreds of millions years ago.
And now horseshoe crabs have spread their pincers into Great Yarmouth with three of the prehistoric-looking creatures making a home at Great Yarmouth Sea Life Centre.
They are part of a new feature area called Claws.
Chris Sturdy, Sea Life curator, said: “Horseshoe crabs have to keep walking when eating as their jaws operate on the same system as their leg and they swim upside down.
“They have bright blue blood which scientists have discovered can be used to check for potentially dangerous endotoxin bacteria in medicines.
“In the US blood is regularly taken from the Florida variety of horseshoe crabs for this reason, but the crabs are then released back into the wild.”
The creatures’ ancestors date back to about 450 million years ago. They famously come ashore to mate and lay eggs.
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