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Horseshoe Crab
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The Horseshoe Crab (also known as the King Crab) is a hard-shelled invertebrate that lives in warm, shallow coastal waters on the sea floor. It is not really a crab; it is more closely related to arachnids (spiders and scorpions). The Horseshoe Crab first appeared about 500 million years ago (during the Ordovician Period), and has changed very little since. There are four species of Horseshoe Crabs alive today; they live off the coasts of India, Japan, Indonesia, the eastern USA, and the Gulf of Mexico.

Diet: The Horseshoe Crab eats sea worms and mollusks (like young clams). They find their prey while walking along the sea bed; they are predominantly nocturnal (most active at night).

Anatomy: The Horseshoe Crab has a hard outer shell (an exoskeleton), 5 pairs of jointed legs and a pair of pincers. The Horseshoe Crab is up to 2 ft (60 cm) long and weighs up to 10 pounds (4.5 kg); it molts its skin many times as it grows. The male is two-thirds the size of the female. The long tail is not a weapon; it is used as a rudder (for steering) and for righting itself when it is flipped upside down. The Horseshoe Crab has light blue, copper-based blood. It breathes using book gills, thin plates located on the abdomen.

Reproduction: Horseshoe Crabs hatch from eggs that the female lays. She lays roughly 20,000 small, green eggs in holes that she digs in the sand on the beach.

Classification: Phylum Arthropoda, Class Merostomata, Order Xiphosura, Genus and species Limulus polyphemus, Tachypleus tridentatus, T. gigas, and Carcinoscorpinus rotundicauda.

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