A whale’s flipper, a monkey’s arm, and a horse’s foreleg all look very different. Yet these animals gave the same basic combination of bones in their forelimb, as do all other mammals. Each has adapted to its environment after millions of years of evolution from a common ancestor. With its long, thin bones, a bat’s forelimb is adapted for flying. With its short, strong bones, a mole’s forelimb is adapted for digging.
Within every species there are always differences between individuals. Some may be better at finding limited food, or at avoiding predators. These individuals are more likely to survive and pass on thier favorable features to their offspring. This process, known as natural selection, enables species to adapt to changing environments, and in time many lead to new species appearing.
Living things change through time in a continual process called evolution. Since life on Earth began, millions of new species have appeared and disappeared. Organisms alive today represent only a tiny proportion of all the living things that have ever existed. Evolution occurs largely as a result of natural selection. This process favors the survival, and thus the ability to reproduce, of individuals that are better adapted to their environment than other members of the same species.
Painted rock lobster is a brightly colored crustacean that belongs to a group of species called spiny lobsters. Instead of claws, spiny lobsters have long, sharp-edged antennae that they use as weapons when threatened. The painted rock lobster usually lives in shallow water. Like many of its relatives, it tends to feed at night and live in large groups.
Shore crab is a very active crab that survives by searching for anything edible along the shore. Although it has to keep its body moist, it is equally at home in or out of the water. It uses its back legs like paddles when swimming, and its claws for collecting food and defending itself. If it loses a claw, it slowly grows another.
Wood louse is also known as sow bugs, wood lice are among the few crustaceans that live permanently on land. Unlike insects, they do not have waterproof skins, and unless they kept moist they will die. A wood louse’s body has many similar looking segments. Its thoracic segments bear legs, and its abdominal segments have flaps that collect oxygen from the air. These work only if covered by a film of water.
Krill are an important part of Antarctic food chains. These small crustaceans feed on microscopic plants and animals, and are eaten by whales, seals, birds, and fish. Krill live in the Antarctic Ocean, where they form gigantic swarms close to the water’s surface. these can contain 25 billion animals.
Red hermit crabs have soft abdomen unlike most crabs. They use old shells from other animals for protection. They grow during their adult life, and often have to move to a bigger shell. The red hermut crab is one of the largest species of crabs. It uses its long claws to catch small animals and pick up pieces of food.
Crustaceans is a group of arthropods that includes crayfish, lobsters, crabs, and shrimp. Most have a body with three parts - head, thorax, and abdomen - but in some species the head and thorax are joined. All live in the water, except wood lice and their relatives.
After insects, mollusks are the largest invertebrate group. They include gastripods, such as slugs and snails;
bivalves, such as clams and oysters; and cephalods, such as cuttlefish, octopuses, and squid. Many have a hard shell, and feed with a rasping, toothed tongue.