Genera: Carcinoscorpius, Limulus, Tachypleus
Species: C. rotundicauda (Mangrove Horseshoe Crab), L. polyphemus (Atlantic Horseshoe Crab), T. gigas (Indo-Pacific Horseshoe Crab), T. tridentatus (Chinese or Japanese Horseshoe Crab)
Common Names: Horseshoe Crab
Horseshoe crabs spend much of their time on the sea floor in search of food, which mainly includes molluscs, worms, and crustaceans.
As they grow, horseshoe crabs undergo “molting”, a process in which they shed their exoskeleton (shell), as a larger one takes its place. They will do this up to 16 or 17 times before adulthood.
Horseshoe crabs often live in deep ocean waters for much of the year, but travel to coastal near-shore areas to breed. Females lay between 60,000 and 120,000 eggs. The reason so many eggs are laid is due to high levels of predation, as many young horseshoe crabs are eaten by shore birds and other predators.
Horseshoe crabs are named for the hard shell (or carapace) that surrounds their body, which is shaped like a horseshoe. Their entire upper body is enclosed in this protective “armor”, while their undersides reveal their ten legs and “book gills”, which help them in both breathing and swimming. A long, straight tail pokes out from behind their shell.
The largest species of horseshoe crab, the Chinese horseshoe crab, can grow up to 31 inches long (including the tail), while the smallest, the mangrove horseshoe crab, only grows to about a foot long.
Though they look somewhat fearsome and have a reputation for being venomous or dangerous, horseshoe crabs are in fact completely harmless and pose no danger to humans.
Horseshoe crabs have been around for over 300 million years. Their overall body design and shape has largely remained unchanged during that huge span of time. They are the only living members of their order, Xiphosura. Despite being commonly called crabs, their closest living relatives in the subphylum Chelicerata are the arachnids, including spiders and scorpions.
While there are currently four living species of horseshoe crab in three genera, there are several more extinct species known from the fossil record.