Crustaceans are arthropods adapted to life in the oceans, with a hard shell and biramous limbs. They include lobsters, crabs, and barnacles, as well as terrestrial species like land crabs and woodlice. Lesser-known crustaceans include giant isopods and crustacean lice, such as the whale louse.
Crustaceans are arthropods, like insects, but unlike their cousins, they have mostly adapted to life in the oceans. The term “crustacean” comes from the Latin word crusta which means “crust, shell or hard surface”. Like other arthropods, crustaceans have a hard shell, often thicker than its insect cousins, and mandibles used for handling and consuming food. Crustaceans are distinguished from other arthropods by being a monophyletic group (descended from a common ancestor) and possessing biramous (branched) limbs.
Crustaceans include many familiar animals: lobsters, crayfish, barnacles, crabs and crayfish. There are also terrestrial crustaceans, such as land crabs, woodlice and land hermit crabs. There are billions of woodlice in a typical forest, and some Pacific islands are literally teeming with land crabs. Some, such as the coconut crab, are huge, with a leg span of 2 m (6 ft) and weighing up to 4 kg (9 lb). The coconut crab is the largest living land arthropod, capable of crushing coconuts with a single hammering motion of its claws. It also occasionally consumes mice and will attack a human if threatened, though no fatalities have ever been reported.
There are some lesser known crustaceans. One is the giant isopod, Bathynomus giganteus, foot-long relatives of woodlice that slowly traverse the ocean floors, eating detritus. The giant isopods, accustomed to the relatively desert environment of the deep ocean floors, are able to go for two whole months without food. These animals were discovered for the first time by the French zoologist Alphonse Milne-Edwards in 1879, after having fished a specimen from the Gulf of Mexico. At the time, the discovery was lauded by scientists and the public alike and helped demonstrate that the ocean floor wasn’t entirely devoid of life. Yet, to this day, there are many people who have never heard of the giant isopod, and after seeing pictures of giant isopods, consider them models or the result of photoshop.
Another unknown class of crustacean are the crustacean lice, which infect every imaginable ocean creature. The hideous whale louse, found in the skin lesions, genital folds, nostrils and eyes of whales, can grow to the size of a thumb.
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