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Atlantic Horseshoe Crab1 locationSea Creature
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Jul 11 2014
Cape Cod Family Reunion
TypeSea Creature
FamilyLimulidae - Crabs
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Limulus polyphemus

From Wikipedia

The Atlantic horseshoe crab,is a marine chelicerate arthropod. Despite its name, it is more closely related to spiders, ticks, and scorpions than to crabs. Horseshoe crabs are most commonly found in the Gulf of Mexico and along the northern Atlantic coast of North America. A main area of annual migration is Delaware Bay, although stray individuals are occasionally found in Europe.

Horseshoe crabs are often referred to as living fossils, as they have changed little in the last 445 million years. Forms almost identical to this species were present during the Triassic period 230 million years ago, and similar species were present in the Devonian, 400 million years ago. However, the Atlantic horseshoe crab itself has no fossil record at all, and the genus Limulus "ranges back only some 20 million years, not 200 million."

Horseshoe crabs have three main parts to the body: the head region, known as the 'prosoma', the abdominal region or 'opisthosoma',the spine-like tail or 'telson'. The smooth shell or carapace is shaped like a horseshoe, and is greenish grey to dark brown in colour. The sexes are similar in appearance, but females are typically 25 to 30% larger than the male and can grow up to 60 cm (24 in) in length (including tail).

Horseshoe crabs possess the rare ability to regrow lost limbs, in a manner similar to sea stars.

The mouth opening is between the legs, and the gills are visible below.

The brain and the heart are located in the prosoma. On the underside of the prosoma, six pairs of appendages occur, the first of which (the small pincers or chelicerae) are used to pass food into the mouth, which is located in the middle of the underside of the cephalothorax, between the chilicerae. Although most arthropods have mandibles, the horseshoe crab is jawless.

The first four pairs of legs have claws, the last pair has a leaf-like structure used for pushing.

The telson (i.e., tail or caudal spine) is used to steer in the water and also to flip itself over if stuck upside down.

Among other senses, they have a small chemoreceptor organ that senses smells on the triangular area formed by the exoskeleton beneath the body near the ventral eyes

Medical uses
Horseshoe crabs are valuable as a species to the medical research community, and in medical testing. The clotting reaction of the animal's blood is used in the widely used Limulus amebocyte lysate (LAL) test to detect bacterial endotoxins in pharmaceuticals and to test for several bacterial diseases.

Enzymes from horseshoe crab blood are used by astronauts in the International Space Station to test surfaces for unwanted bacteria and fungi.

A protein from horseshoe crab blood is also under investigation as a novel antibiotic.

LAL is obtained from the animals' blood. Horseshoe crabs are returned to the ocean after bleeding, although some 3% die during the process. Studies show the blood volume returns to normal in about a week, though blood cell count can take two to three months to fully rebound
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