Mating adult horseshoe crabs.

Blue blood and carapace with many eyes

The first ancestor of today's horseshoe crabs lived around 400 million years ago. A round, solid and nearly closed carapace give these ancient sea creatures an archaic, fortified character. Nevertheless, the few populations of these seemingly strange "living fossils," which can reach a total length of 75 centimeters, are now endangered.

Horseshoe crabs are not, as their name suggests, crustaceans, but are instead more closely related to spiders. These animals have ten eyes and its single eye spot protruding from its shell gives rise to its Latin name, which means “small squinting cyclops.” Their behavior is just as unusual as their appearance. These animals emerge from their habitat at depths of around 50 meters and make for the beach to lay their eggs, leaving behind some rather strange creeping tracks. The centimeter-long larvae deposited in the sand wells dug by the crabs on the beach later return to the water with the tide. There, they grow to reach their final size through regular molts, only becoming sexually mature after ten years.

Despite the rigid shape of their shell, horseshoe crabs are fairly mobile. The youngsters can even swim. They do this belly side up, paddling with their feet. Thanks to spoon-like attachments on their last pair of legs, adults are able to move across sand and mud. They use their long tail to defend themselves and to flip themselves over if turned upside down.

The eight specimens on display at the OZEANEUM originate from the Atlantic coast of the United States and came to the museum on a fishing boat in 1974. The threat facing the four known species in the Atlantic and Pacific are the result of the horseshoe crab’s blue, copper-rich blood. It is used for toxicological testing in the pharmaceutical industry. Nevertheless, these animals are under strict protection.