Horseshoe Crab

ID points

• Horseshoe-shaped hard shell followed by a long stiff sword-like tail
• Five pairs of walking legs on the underside, all hidden beneath the shell
• The blood is blue, and it is not a crab but a relative of spiders

Basics

Family

Limulidae

Length

30–60 cm

Depth

0-30 m

Regions

Indo-Pacific reefs · Caribbean & W. Atlantic

Distribution

Shallow sandy bottoms and the intertidal zone

Habitat

Shallow sandy bottoms and intertidal zone

Diet

Worms, molluscs

Easily confused with

Ribbontail RayRound disc-shaped body with thin soft edgesAngel SharkFlattened like a ray, but the gill slits open on the sides of the bodyBlue-spotted Ribbontail RayRings of vivid electric blue spots on a yellow-brown ground

Fun fact

Horseshoe crab blood is blue, because it carries copper-based haemocyanin. An extract of that blood, known as LAL reagent, is the gold standard the medical industry uses to test for bacterial endotoxins, and it saves countless lives every year.