They are invertebrates. They have jointed legs and hard outer coverings called exoskeletons that protect their soft bodies. Horseshoe crabs are not really true crabs. True crabs have only one pair of claws. Horseshoe crabs have more.
True crabs have antennae or feelers on their heads and jaws.
Horseshoe crabs don't. Below is how scientists classify the horseshoe crabs in the Delaware Bay.