Marine Biology

Horseshoe Crabs



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Opinions about Horseshoe Crabs vary wildly. Are they ugly? Are they cute? Are they just plain weird? From the chitinous, boomerang-shaped "shell" studded with composite eyes, to the five sets of spidery legs and the sharp tail spine that juts out from the rear, the Horseshoe Crab is, at the very least, an unusual animal. Although they look somewhat like an alien, have green blood and ten eyes, Horseshoe Crabs have lived right here on earth for billions of years. Fossils suggest they predate almost all life on land, birds, dinosaurs, even flowers. They are closely related to Trilobites, one of the oldest known multi-cellular lifeforms.

Horseshoe Crabs are Chelicerate Arthropods. This means that, despite their common name, they are NOT Crabs. The Horseshoe Crab, which is also sometimes called the "King Crab," has more in common with Spiders than Crustaceans.

Their name and outward appearance are far from their only unusual qualities. Horseshoe Crabs have a hemocyanin-based circulatory system. This means that they are one of the only known species which has copper-based green blood. Not only that, injured Horseshoe Crabs can regenerate lost limbs, in much the same way as a Sea Star, and their bodies naturally produce a substance used medicinally to test whether intravenous needles are contaminated by endotoxins.

Although primarily aquatic, Horseshoe Crabs are born on the beach. After hatching, they travel, sometimes for days, heading underwater and toward the inter-tidal flats. As they mature, the young crabs will move into shoals, burrowing into the sand during the day, and feeding during the night on mollusks, worms, and other invertebrates. Although Horseshoe Crabs will spend most of their lives underwater, they will return to the beach again to spawn.

For over 250 million years, Horseshoe Crabs have remained unchanged. Although the prime spawning beaches have been becoming scarcer in recent years, Horseshoe Crabs are not yet endangered, and are a common sight on the American east coast. Large, brown, and spiked, their physical shape was always a means of protection, and was never intended to appeal to human aesthetics. However, some people still insist that, in a strange way, they ARE kind of cute.

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