Atlantic Horseshoe Crab

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Project Description

Atlantic Horseshoe Crab

Limulus polyphemus

Range/Geographical Distribution: Maine to Florida and the Gulf of Mexico.

Habitat: Juveniles are found on intertidal sand flats but adults can be found to depths of 600 feet.

Description: The body of a horseshoe crab is divided into three parts: the prosoma, opisthosoma and telson, or tail. The prosoma is the front, semicircular part and the opisthosoma, which protects the gills, is attached to the prosoma with a hinge. The top of the shell has ridges and spines.  Seven pairs of leg-like appendages are found under the shell.

Size: Can grow up to 24 inches in length.

Food: Mollusks, annelid worms, and other benthic invertebrates.

Breeding: Mate during the full and new moons of May and June. Males patrol near-shore waters for mates and are attracted to females by pheromones. The males hook their specially modified second set of appendages onto the body of a female.  The female drags the male onto a sandy beach and uses her pusher legs to form a shallow nest between the high- and low-tide lines. Then the female deposits five to seven clumps of 2000-4000 eggs and drags the male over the eggs to fertilize them.  Females can lay more than 90,000 eggs in one year. The larvae hatch and leave their nest during a high tide.  After one molt the larvae enters its first juvenile stage.  Females mature at ten to eleven years and males at eight to nine years.

Predators: Sea turtles, and alligators.

Conservation Status: Listed as near threatened by the IUCN red list; harvesting and habitat destruction have drastically reduced its numbers in some locations.

Interesting Facts:  Horseshoe crabs have contributed to the medical research community. A substance in their blood called Limulus Amebocyte Lysate is used to test for bacterial endotoxins in pharmaceuticals and for several bacterial diseases.  Also, much of what we know about the function of our eyes is the result of studies that began in the 1960s on the large, compound eyes of the horseshoe crab.  Horseshoe crabs have no jaws or teeth but they use the base of their legs to grind up clams and they have a gizzard.

On the Coast:  Live horseshoe crabs can be seen on Georgia’s beaches during mating.  Molts (shed exoskeletons) commonly wash up onto the beach year round.

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