Horseshoe Crab (3) cm 29 Carcinoscorpius rotundicauda

The Horseshoe crab or royal crab, are indeed Arthropods Chelicerata, unique survivors of Merostomata, which had in the Paleozoic, with their representatives Gigantostracs (Euripterids or scorpions sea) a huge evolutionary success. Despite its common name in English ( "horseshoe crab"), arising from the particular shape and looking armored body, this animal is more closely related to spiders and scorpions that with the class of crustaceans.
There are still only four species belonging to the family Limulidae, and are the Limulus polyphemus, (previously classified as Limulus cyclops, Xiphosura American, Polyphemus occidentalis), widespread on the east coast of North America, from Maine to southern Florida, and in the Gulf of Mexico to the Yucatan peninsula, the Japanese horseshoe crab (Tachypleus gigas), common in the Seto Inland Sea, and two species (Tachypleus tridentatus and Carcinoscorpius rotundicauda) located on the east coast of India.