Living creatures on Earth need three basic things in order to survive: theability to eat, breath, and reproduce. All animals are able to do so. Animalsare divided into species, among these species are: Mammals, Reptiles,Arthropods, and Aves. Mammals, also known as Mammalia, come from Latin meaningmamma breast. They are called this due to the fact that Mammals are the onlyanimals which have mammary glands, which enable them to nourish their youngsolely on milk secreted from these glands. Mammals are warm blooded, and all,except for marine mammals, are mostly or completely covered with hair.

Mammalsgive birth to live young, however, there are a few rare exceptions to this rule.A few mammals, such as the platypus, lay eggs instead of having live young. Yetonce the eggs are hatched the females do have mammary glands, and produce milkfor their young. Another feature of mammals is that their heart has fourchambers and a muscular diaphragm that separates their chest and abdominalcavity. The mammal class includes: Dogs, cats, horses, beavers, dolphins, batsand humans. Another animal species are Reptiles, also known as Reptil which isLatin for Reptus, meaning to crawl. Reptiles are usually hairless with dry,scaly skin. They are cold-blooded, which means in order for them to maintain astable body temperature, they must be exposed to some heat source, such as thesun, or a rock warmed by the heat of the day.

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Due to the need for warmth,Reptiles are naturally found in warm, dry climates. All reptiles, except forsnakes, have low slung bodies with long tails, balanced on four awkwardly smalllimbs. Although there are a few aquatic Reptiles (Reptiles who live mainly inwater), they all must come up to the surface for oxygen. Reptiles do not givebirth to live young. Instead, they lay eggs on land. The female usually buriesthe eggs in warm dirt or sand to incubate them. Reptiles do not have mammaryglands therefore, their young are not dependent on their mother for food andsoon after birth, they must learn to obtain food for themselves.

The Reptileclass includes: turtles, alligators, snakes, lizards, and dinosaurs. The animalspecies that makes up over eighty percent of all species are Arthropods.Arthropod comes from the Latin word, Arthropoda, meaning foot. Arthropods tendto have many legs and feet, giving purpose to their name. Arthropods areinvertebrate, which means they have no backbone. Unlike other animal species,Arthropods have what is called an exoskeleton which is an external skeleton orshell. The exoskeleton is jointed, allowing Arthropods to move, and as the theygrow, their exoskeleton sheds, or molts, and a new, larger one grows to replaceit. All Arthropods lay eggs and care for them, yet when they young are born,they are immediately independent.

The Arthropod class includes: insects,spiders, centipedes, and crabs. A very beautiful, yet simply diverse animalspecies are Aves. Aves, also known as Birds, are warm-blooded, egg-layinganimals. Aves are covered with feathers and its forelimbs are wings. Likemammals, birds have a four-chambered heart; they have a relatively large brainand acute hearing but little sense of smell. Aves are highly adapted for flight.

Their feathers, though light, protect against cold and wet and have greatstrength. Aves are well known for their beautiful whistle, or song, yet thesinging ability is usually restricted to, or superior in, the male. Most birdsbuild some kind of nest for their eggs, which vary in size, shape, color, andnumber according to species.

Their young are cared for by the parents until theyreach maturity. The class of Aves include: geese, flamingos, humming birds, andpenguins. Each of these animal species are very unique and crucial to the Earth.Without these diverse creatures, the world would not have the variety and beautyit beholds today.Zoology and Animals