Living creatures on Earth need three basic things in order to survive: the
ability to eat, breath, and reproduce. All animals are able to do so. Animals
are divided into species, among these species are: Mammals, Reptiles,
Arthropods, and Aves. Mammals, also known as Mammalia, come from Latin meaning
mamma breast. They are called this due to the fact that Mammals are the only
animals which have mammary glands, which enable them to nourish their young
solely on milk secreted from these glands. Mammals are warm blooded, and all,
except for marine mammals, are mostly or completely covered with hair. Mammals
give 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. Yet
once the eggs are hatched the females do have mammary glands, and produce milk
for their young. Another feature of mammals is that their heart has four
chambers and a muscular diaphragm that separates their chest and abdominal
cavity. The mammal class includes: Dogs, cats, horses, beavers, dolphins, bats
and humans. Another animal species are Reptiles, also known as Reptil which is
Latin 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 a
stable body temperature, they must be exposed to some heat source, such as the
sun, or a rock warmed by the heat of the day. Due to the need for warmth,
Reptiles are naturally found in warm, dry climates. All reptiles, except for
snakes, have low slung bodies with long tails, balanced on four awkwardly small
limbs. Although there are a few aquatic Reptiles (Reptiles who live mainly in
water), they all must come up to the surface for oxygen. Reptiles do not give
birth to live young. Instead, they lay eggs on land. The female usually buries
the eggs in warm dirt or sand to incubate them. Reptiles do not have mammary
glands therefore, their young are not dependent on their mother for food and
soon after birth, they must learn to obtain food for themselves. The Reptile
class includes: turtles, alligators, snakes, lizards, and dinosaurs. The animal
species that makes up over eighty percent of all species are Arthropods.
Arthropod comes from the Latin word, Arthropoda, meaning foot. Arthropods tend
to have many legs and feet, giving purpose to their name. Arthropods are
invertebrate, which means they have no backbone. Unlike other animal species,
Arthropods have what is called an exoskeleton which is an external skeleton or
shell. The exoskeleton is jointed, allowing Arthropods to move, and as the they
grow, their exoskeleton sheds, or molts, and a new, larger one grows to replace
it. 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 animal
species are Aves. Aves, also known as Birds, are warm-blooded, egg-laying
animals. Aves are covered with feathers and its forelimbs are wings. Like
mammals, birds have a four-chambered heart; they have a relatively large brain
and acute hearing but little sense of smell. Aves are highly adapted for flight.
Their feathers, though light, protect against cold and wet and have great
strength. Aves are well known for their beautiful whistle, or song, yet the
singing ability is usually restricted to, or superior in, the male. Most birds
build some kind of nest for their eggs, which vary in size, shape, color, and
number according to species. Their young are cared for by the parents until they
reach maturity. The class of Aves include: geese, flamingos, humming birds, and
penguins. 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 beauty
it beholds today.