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5 Things I Learned about Horseshoe Crabs

Horseshoe crabs get their name from a rounded carapace, or exoskeleton, that’s u-shaped like a horse’s shoe. They have jointed legs, a hard shell, an exoskeleton and a segmented body, but they don’t have antennae or a jaw. These arthropods are more closely related to spiders or scorpions than they are to what we think of as true crabs, and they are really fascinating (and important) creatures. Here are just a few reasons why:

  1. Tracing the ancestry of these invertebrates would result in a massive family tree. Horseshoe crabs have been around for hundreds of millions of years, even longer than the dinosaurs!
  2. It might not be fine dining, but it gets the job done. A horseshoe crab’s diet consists of sea worms, mollusks and crustaceans. Because horseshoe crabs don’t have jaws or teeth, they’ll break up food between their legs before pushing it into their mouths. Like birds, a gizzard further grinds that food down. Any undigested bone or shell particles are regurgitated.
  3. Their spiky telsons are nothing to fear. They look like barbs or stingers, but those tails are actually pretty fragile. Horseshoe crabs use them to dig, to steer and to right themselves after swimming upside down or being flipped by a wave.
  4. Horseshoe crabs are slow growers. And because that hard exoskeleton doesn’t grow with them, they regularly develop new, slightly larger shells and shed their old ones. It’s a process called molting.  They’ll do this 16 to 17 times before they reach full adult size.
  5. They’re very important animals. Not only do horseshoe crabs play a big role in their ecosystems—providing a source of food for migratory seabirds, sea turtles, alligators and even sharks—but they are also important to human health. Because their blue, copper-based blood quickly clumps up in the presence of bacterial toxins, it can be used to test for contamination in things like injectable drugs, surgical implants and medical equipment.

While there are synthetic alternatives in development, today pharmaceutical companies developing COVID-19 vaccines are using horseshoe crab blood to test for potential bacterial contamination. Pretty amazing, right? Don’t miss these little lifesavers in the Coastal Boardwalk Gallery the next time you visit the Greater Cleveland Aquarium.

Author: Samantha F.

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