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Horseshoe crab

Scientific name: Limulus polyphemus


The horseshoe crab is an arthropod of the Xifosurous group (xifos = sword, ura = tail) that is characterised as having a long moving spine at the end of its body. It is considered a living fossil that has remained unaltered for 300 million years. Although it is a crab, it is closer to spiders than crustaceans.

Its maximum size is 1 m.


They are predators that live on other invertebrates, anelids and above all molluscs, which they discover by digging in the sand.

They eat them whole and then regurgitate the shells and other hard, undisgestable parts, and they can also eat seaweed.

When the times comes for reproduction they approach the beaches, particularly in the areas of estuaries, where a large number of individuals gather. For mating, the male mounts the female, holding on to her back with the nails of its first pair of legs. Once out of the water, on the beach, in the same position, the female digs a hole in the sand and lays her eggs, which the male immediately irrigates with his sperm. They lay some 200 or 300 eggs that remain hidden in the sand by the inter-tide movement.


The current xifosurous are species of the coast, diggers, which live on silt and sand beds, generally at depths of between 3 and 9 metres.


It lives on the Atlantic coast of North America up to the Yucatan peninsula.


A special almost threatened (according to the red list of endangered species).


With the side of their back, they dig in the sand using their appendices very curiously: they dig their moving spine in to the substrate and rapidly move their legs. Its blood is blue and possesses extraordinary immunological properties of interest to the biomedical industry.


Do you know how the horseshoe crab moves? It swims upside down, head downwards, and uses its moving spine to turn when it wants to walk on the bed.