Crustaceans 101

Built-In Power Armor

If you want to see a real-life armored vehicle, you only have to peer into the nearest tide pool, backyard garden, or deep-ocean trench. Crustaceans are a massive family of creatures—including crabs, lobsters, shrimp, and woodlice (the little roly-polies found under damp rocks)—that wear their bones on the outside. This exoskeleton (an external skeleton) is made of chitin (pronounced KY-tin, a tough material similar to human fingernails), which acts like a biological shield.

But growing inside a hard shell has a major downside: when the animal gets bigger, its armor does not stretch. To grow, a crustacean must undergo molting (shedding its old shell). It cracks open its old armor, crawls out looking soft and wrinkly, and pumps itself up with water to stretch out its new, larger skin before it hardens. During this brief window, the animal is as soft and vulnerable as a peeled grape, forcing it to hide in dark rocky crevices until its new armor solidifies.

Swiss Army Limbs

Crustaceans are the ultimate multi-taskers. While humans use arms for carrying and legs for walking, crustaceans have evolved specialized appendages (limbs) that do almost everything.

Many species have ten legs, but these limbs are not just for walking. Some crustaceans have front legs tipped with heavy claws capable of cracking open clams like nuts. Others have rear legs shaped like paddles for swimming backward at high speed. Many crabs even taste their food using tiny sensory hairs on their legs, deciding if a shell is worth opening before they even pick it up. Meanwhile, their long antennae sweep the water like radar dishes, sensing chemical signals to “smell” danger.

Giant Spiders and Sonic Blasters

This family group includes some of the most extreme body designs on Earth. The Japanese spider crab has a leg span of 12 feet (3.8 meters)—wider than a standard soccer goal. On the other end of the scale, microscopic water fleas are smaller than a single pixel on a phone screen. Some species even have built-in weapons. The pistol shrimp snaps its specialized claw so fast it shoots a jet of water that creates a scorching bubble of heat, knocking out fish instantly with a mini sonic boom.