Ask the Aquarium: Molt or Horseshoe Crab?
Q. I found what I thought was a dead horseshoe crab on the beach. A passerby said he thought it was a molt. Is there a way to tell?
A. Usually, you can tell a horseshoe crab molt by the long, curved slit just under the upper front edge of the shell. This is where the animal squeezed its body out of the old shell.
Horseshoe crabs (Limulus polyphemus) outgrow their shells and must molt to accommodate their increasing size. The new shell is soft at first, but hardens in about 24 hours. With each shedding, the crab is about a fourth larger than before. Molts often wind up washed on shore.
Surprisingly, this armored tank of a crab has 10 walking legs, making it more closely related to spiders and scorpions than to crabs.
Considered a living fossil, these ancient animals have remained virtually unchanged for more than 300 million years. The crabs feed by crawling along the ocean floor in search of worms, mollusks, dead fish and other tidbits.
For mating and egg laying, horseshoe crabs make their way into shallow shoreline waters. From spring to early summer, females lay 2,000 to 3,000 eggs in a series of sandy depressions along the water's edge. The males are close behind to fertilize the eggs. Some two weeks later, baby horseshoes emerge, looking like miniature forms of their parents.
The little crabs head for deeper water, where they remain until sexual maturity some 9 to 11 years later, before traveling back to the shallows to lay eggs of their own.
Despite a menacing appearance and a dagger-like tail, the horseshoe crab is harmless. The tail, called a telson, is used as a lever to right itself when strong waves or currents flip the crab onto its back.
The state operates three public aquariums: one in Pine Knoll Shores, another at Fort Fisher and a third on Roanoke Island. The aquariums are administered by the North Carolina Department of Environment and Natural Resources, and are designed to inspire appreciation and conservation of North Carolina's aquatic environment. For more information about the Aquariums, visit www.ncaquariums.com, or call (800) 832-FISH.
Sherry White works for the public affairs office of the N.C. Aquariums.
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