Class MerostomataThere are only four species of Horseshoe Crabs left in the world. These living fossils have not changed much for the last 400 million years! They are not crabs and are more closely related to spiders and scorpions. Singapore has two of the four species, but these animals are in peril due to the trash that litters our coasts. Many get caught in abandoned fishing nets and die as a result. Fortunately, the Nature Society (Singapore) has a team going all out to do the coastal clean-up.
The two species in Singapore are Coastal Horseshoe Crab (Tachypleus gigas) and Mangrove Horseshoe Crab (Carcinoscorpius rotundicauda). The Coastal Horseshoe Crab is larger, usually greyish and has a triangular tail. The Mangrove Horseshoe Crab is smaller, usually dark-coloured and has a round tail.
The other two species are the Chinese Horseshoe Crab (Tachypleus tridentatus) and the Atlantic Horseshoe Crab (Limulus polyphemus).