Delaware SuperGraphic

The Horseshoe Crab

Though they are called "crabs," and were considered at one time to be true crustaceans, they are actually arthropods and more closely related to the spider and scorpion. Crabs have two pairs of antennae, a pair of mandibles, a pair of claws and four pairs of legs. Horseshoe crabs do not have mandibles or antennae, but do have a pair of small pincers in front for handling food such as worms and shellfish. They also have five pairs of legs, including four pairs with pincers. Horseshoe crabs collect their food with the base of their legs and push it into their mouths, which are located between their legs. This amazing creature's body is divided into three parts: the front domed-shaped prosoma; the middle, spin-edged opisthosoma and the tail which is known as the telson. The telson's main function is to help the horseshoe crab turn over when they are flipped, and it is not poisonous as one would assume at first glance. Their legs are attached to the underside of the prosoma while book gills are attached to the opisthosoma.

The horseshoe crab has numerous photoreceptors on its top shell, running down the length of the telson. These photoreceptors are sensitive to light and help synchronize the animal's internal clock with daily cycles of light and darkness.

What's also fascinating is that horseshoe crabs molt like birds as they outgrow their shells. When these strange creatures start feeling a little cramped in their existing shell, they absorb water to make their bodies swell and they burst out of their old shells. This gives a new meaning to "taking a load off your shoulders!" But it is not too long until they get a new outfit - magically, they already had a new, bigger shell underneath that hardens in just one day.

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