FREE ESSAY ON ANIMAL SPECIES

ANIMAL SPECIES

Holly Ratliff
July 5, 2000
Beckley
English 2
Animal Species
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.