This red land crab has a thick exoskeleton.
Hide and Seek A coral crab has a good shell defense, too. I saw how it stays safe on a diff erent expedition. I was swimming over a reef. Just below me, colorful corals spread across the seafloor. My eyes scanned the reef. Finally, I saw a shape on a coral that looked a little diff erent. It was a tiny pink and white crab. As it
Body Armor T e first thing I always notice when I find a crab is its shell. A crab is an invertebrate, so it doesn’t have a backbone, or any bones at all. Instead, a hard exoskeleton covers its body. An exoskeleton protects a crab no matter
where it lives. T is body armor is so hard that many predators can’t bite through it. Not all exoskeletons are the same, though. Each species of crab has developed an exoskeleton that helps it survive in its environment.
Looking Sharp Some crab exoskeletons are like weapons. I learned that the hard way on a trip to the South China Sea. Little is known about what lives deep in the sea here. To find out, we pulled up nets of sea life from 3,000 m deep. T is sea life looked like a jumble of
seaweed, algae, and other seafloor debris. My job was to sort through it looking for creatures. I didn’t wear gloves. Big mistake. When I grabbed a handful of slimy algae, something sharp cut my hand. I’d grabbed a spider crab I hadn’t seen hiding in the algae. T is crab was only 7 cm long, but sharp
spikes covered its exoskeleton. A predator would think twice about taking a bite of that shell! T at’s not the only reason it has spikes. T ey also snag algae and seaweed. T at lets the crab use its environment to camouflage itself. I know firsthand that it works!
6 NATIONAL GEOGRAPHIC EXTREME EXPLORER
clung to pink and white corals, it was hard to see where the crab ended and the reef started. T e crab used its exoskeleton as camouflage to blend in with the corals where it lives.
Water Keeper By watching land crabs, I learned something new about how an exoskeleton can help a crab survive. T ese crabs have developed thicker shells than crabs that live in water. It turns out their shell helps them breathe on land. Like all crabs, a land crab uses its gills to
breathe. Gills remove oxygen from water. Using gills is no problem for a water crab. It lives in the water. Water enters the crab’s body at the base of its claw. It flows through the gills and then out the crab’s mouth. T e constant flow of water brings the water crab a steady supply of oxygen so it can breathe. Land crabs don’t spend much time in
the water. Yet they’ve developed ways to get water to their gills, too. I usually find them hiding in underground burrows. T is damp environment keeps a land crab’s gills moist. Its exoskeleton helps, too. It’s so thick that water inside the crab doesn’t evaporate easily. Instead, it pools inside the crab’s shell. T e land crab doesn’t waste this water.
It recycles it. When water bubbles out of its mouth, the crab catches drops in a hairy patch on its shell. T e hairs soak up dew and ground moisture, too. T e water then flows back into the crab’s body. T at way, the land crab gets the water and oxygen that it needs to breathe.
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