Protective armor, in the form of quills, shells and scales, has helped animals survive predation and harsh environments for centuries. From prehistoric dinosaurs -- who grew thick, armor-like skin -- to an ocean full of mollusks, many animals sport external and superficial armor as a source of protection.
The armadillo, porcupine and hedgehog are all small mammals that have armor-like skin in common. Armadillo (Dasypodidae) means “little armored one” in Spanish, and that name couldn’t be more fitting for the omnivorous mammal with bony plates that cover its back, head, legs and tail. The only mammals that wear such shells, armadillos meander through warm habitats with perpetual shields attached to their bodies. Hedgehogs, members of the Erinaceidae family, curl up into a ball, hiding their vulnerable bodies under a mountain of stiff, sharp spines, when threatened. The porcupine (Erethizon dorsatum) reacts to danger in a similar way. This rodent’s body is covered in quills that lie flat until he is threatened. Once threatened, the porcupine erects his sharp quills as a defense mechanism.
Turtles, tortoises and terrapins are all members of the order Chelonia, which includes hundreds of shelled species. Chelonians have tough, protective shells made up of over 60 bones covered by plates. These hard plates are called scutes. Unlike many shelled marine species, a chelonian is permanently attached to its shell through its spine and rib cage. When it senses danger or feels pressure upon its shell (called a carapace on top and plastron on bottom), a chelonian instinctively pulls its head, legs and feet inside the protective shell.
Arthropods have a tough outer covering -- an exoskeleton -- which they regularly molt as their bodies grow. In the sea, crustaceans, such as crabs and lobsters, use both their pincers and hard exoskeletons as a means of defense. On land, scorpions (members of the arachnid class) employ their exoskeletons in similarly defensive ways.
Mollusks and Echinoderms
Mollusks, such as snails and chitons, have calcified shells. A chiton’s eight shell plates provide protection from marine predators and rough seas, while a snail’s univalve (one-piece) shell protects it similarly on land. Sea urchins are echinoderms that could be thought of as the porcupines of the sea. Their soft, globular bodies are covered with an array of poisonous spines for defense.
A fish’s scales are not only beautiful and aid in fluidity, but they also provide a coating over its skin to protect from parasites. Larger scales can make the fish tougher and harder to digest, while some groups of fish, like sturgeon, still sport primitive, bony scutes on their skin.
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