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Limulus polyphemus
Limulus polyphemus
American horseshoe crabs (Limulus polyphemus) are prehistoric-looking creatures that have not changed in appearance since the Mesozoic Era approximately 200 million years ago, when dinosaurs were alive. Horseshoe crabs refer to "living fossils".
Male
Male
A male horseshoe crab is smaller and more slender than a female. His most distinctive feature is a pair of hook-shaped front claws, which differ from the female's claw-like pincers. He has a hard protective shell, several eyes around his body, walking legs underneath, and book gills for breathing. Like the female, he uses his long tail spine for balance and to right himself if overturned.
Female
Female
A female horseshoe crab is larger than a male and has a wide, rounded shell that is usually brown, gray, or olive green. Short spines line the edges of her body, giving her a rugged appearance. Underneath are strong walking legs and small claws that help move food to her mouth. She also has several eyes that can detect light and movement, and a long tail spine that helps her balance and flip over
Range
Range
Horseshoe crab populations range from the Gulf of Maine to Florida and along the Atlantic coast. The species range extends into the Gulf of America from Florida west into Louisiana and south to the Yucatán Peninsula. The species is considered to be absent from Texas to Tabasco, México.
Size & Shape
Size & Shape
This horseshoe crab has a primitive body structure that is composed of three parts: the prosoma(head), the opisthosoma(central area), and the telson(tail). The telson helps the crab to flip itself right side up if it's being turned over. The largest adult females can be found along the Georgia coast, where it can reach the size of 30 cm across the prosoma and length of 60cm when the tail is included. Its prosoma resembles the shape of a horse's shoe, that's where its name comes from.
Weight
Weight
Limulus horseshoe crab's size varies along the Atlantic coast. The largest individuals, still, can be found along the Georgia coast with the mature female that grows to about 4.8 kg. Males are typically smaller than females by 25-30%.
Color & Pattern
Color & Pattern
Horseshoe crabs are greenish grey to dark brown in color when viewed from above, and the underside appears brownish in appearance.
Life Cycle
Life Cycle
Horseshoe crabs are characterized by high fecundity, or ability to have a large offspring, as well as high egg and larval mortality and low adult mortality. They breed in late spring on low-energy coastal beaches along the Atlantic and Gulf of America coasts in the United States, laying eggs in nests buried in the sand. Larvae hatch from eggs within two to four weeks, although some larvae may overwinter within nests and hatch out the following spring. Planktonic larvae typically settle within one to two weeks of hatching and begin molting as they grow. Juvenile crabs remain in intertidal flats, usually near breeding beaches. Older individuals move out of intertidal areas to deeper waters.
Reproduction
Reproduction
During full moon nights primarily in May and June, new moon nights and some high tide nights in spring, hundreds of thousands of horseshoe crabs crawl up the shoreline along the Atlantic coast to mate and lay their eggs. Females lay around 4,000 eggs in clusters. She will do this a number of times until she has laid 20,000 eggs a night and up to 100,000 each season. Most of these eggs will not survive to maturity, as they are an important food source for sea turtles, fish and migratory birds.
Horseshoe crab babies look just like adults, but with soft, transparent shells. They will molt up to 16 times before they are full-grown
Food & Eating Habits
Food & Eating Habits
Horseshoe crabs eat worms, crustaceans, small mollusks and algae. They use their chelicerae—the little grabbing appendages around their mouths—to pick up food, which is then passed back to their bristle teeth for chewing and then back up to their mouths for swallowing. Bigger horseshoe crabs eat mollusks, while smaller ones tend to eat prey that is softer and easier to catch.
Lifespan
Lifespan
In the wild, they can live for 20 years or more.
Eating Habits
Eating Habits
They eat at night. They have nine eyes near their tail, giving them exceptionally good vision even in low light.
Horseshoe Crab Facts!
1. Horseshoe crabs predate the dinosaurs.
2. Horseshoe blood is blue.
3. They have six pairs of legs but only five are for walking.
4. One horseshoe crab can lay about 4,000 eggs.
5. Horseshoe crab babies look just like adults but with translucent shells.
6. Many shorebirds can’t survive without horseshoe crabs.
7. They are not true crabs.
8. Horseshoe crab blood detects bacteria and ensures medical equipment are safe for use.
9. A horseshoe crab’s pointed tail is not for self-defense.
10. They glow under UV light.
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