Download Diversity of Animals

Diversity of Animals
Animals can be classified and grouped based
on similarities in their characteristics.
Classifying Animals
Animals make up one of the major biological groups of classification. All animals are multicellular
organisms. Since they cannot make their own food, animals must consume other organisms in order
to receive energy. Most animals also have the ability to move and undergo sexual reproduction.
The major classification group including all animals can be further divided into vertebrates and
invertebrates.
Invertebrates
Invertebrates are animals that do not have a backbone, or any other types of bones. However, many
invertebrates do have an exoskeleton, or a hard outer skeleton, for support. A snail at the beach, an
insect in a tree, and an earthworm in the soil are all kinds of invertebrates.
The invertebrate group is made up of a variety of organisms, including
sponges, starfish, octopuses, snails, insects, earthworms, crustaceans,
jellyfish, and coral.
The invertebrate group can also be divided into many smaller classification
groups. For example, two major groups of invertebrates are mollusks and
arthropods.
Octopuses and snails are both kinds of invertebrates that are classified as mollusks. Most mollusks have a hard shell they can pull into to protect
the soft parts of their bodies. They usually have a muscular
foot that allows movement or can open and close their shell.
Snails, clams, slugs, squid, and octopuses are all examples of mollusks.
Ants and lobsters are both kinds of invertebrates that are classified as arthropods. Arthropods are invertebrates that have an exoskeleton,
a segmented body, and jointed legs. This group includes
crustaceans (like lobsters and crabs), insects (like ants
and fleas), and spiders.
Vertebrates
Vertebrates are animals that have backbones. They include a variety of organisms that can be further
divided into smaller classification groups. These groups are fish, amphibians, reptiles, birds, and
mammals.
Clownfish and sharks are classified as fish.
Fish are cold-blooded vertebrates that live in water.
They obtain dissolved oxygen from the water through
their gills. Most fish also lay eggs and have fins and
scales. Salmon, clownfish, tuna, sharks, trout, snapper, and swordfish are all classified as fish.
Frogs and salamanders are classified as amphibians.
Amphibians are cold-blooded vertebrates. Most
amphibians can breathe underwater with gills when they are
young and then undergo metamorphosis at a certain age.
Most adult forms breathe air using lungs, but many can also
"breathe" through their skin. Frogs, toads, and salamanders are the three major kinds of amphibians.
Snakes, turtles, and crocodiles are classified as reptiles. Reptiles are cold-blooded, have scales or plates on
their bodies, and have lungs that breathe air. Most
reptiles also lay eggs and live at least part of their
lives on land. Examples of reptiles include snakes, lizards, turtles, and crocodiles.
Ducks, ostriches, and parrots are all vertebrates that are classified as birds.
Birds are vertebrates that breathe air with lungs, are warmblooded, lay hard-shelled eggs, and have feathers, two feet,
two wings, and toothless beaks. Examples of birds include
parrots, eagles, penguins, hawks, chickens, ducks, turkeys, and ostriches.
Dolphins, elephants, and wolves are all vertebrates that are classified as mammals. Mammals are warm-blooded vertebrates that breathe
air with lungs, have sweat glands, produce milk to feed
their young, and have fur or hair. Most mammals also have babies that are born live. Humans, bears,
dogs, cats, elephants, dolphins, whales, squirrels, foxes, giraffes, rabbits, and wolves are all
examples of mammals.
Characteristics of Animals
An animal is a living thing that eats other organisms for food and can move from one place to another
for at least part of its life. Animals are classified, or divided into groups, based on similarities and
differences.
Animals can differ from one another in the way that they are shaped or in the way that they
reproduce, respire, digest food, or circulate blood.
Reproduction
One of the differences among different kinds of animals is the way they reproduce. Some produced
through asexual reproduction, whereas others reproduce through sexual reproduction. There are
advantages and disadvantages to both sexual and asexual reproduction. The lifestyle of an
organisms is related to how and when it reproduces.
Asexual Reproduction—Asexual reproduction is the easiest form of reproduction. Organisms do
not have to use energy to find mates because only one parent is required. The offspring are generally
identical to parents, and there is usually very little variation of characteristics within the population.
So, it is more difficult for organisms that reproduce asexually to adapt to the changes in their
ecosystems.
Asexual reproduction is usually linked to the simplest animals, like sponges and hydras. However,
there are a few vertebrates that reproduce asexually. In this case, the parents and offspring are all
females. Examples of asexual reproduction in animals include:
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budding - sponges and hydras
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fragmentation - flat worms
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parthenogenesis - whiptail lizards
Sexual Reproduction—Most animals reproduce sexually. Sexual reproduction usually requires
two parents. However, some animals are hermaphroditic, which means they produce both sperm and
eggs. Animals that produce both sex cells have a higher chance of finding a mate than animals with
separate sexes because any animal of the same species that they encounter is a potential mate.
Other animals, like humans, have separate female and male organisms within the species.
Sex cells produced by the females must combine with sex cells produced by the males in a process
called fertilization. During fertilization, egg cells and sperm cells fuse to produce an offspring.
Fertilization can be internal or external.
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Internal fertilization
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egg and sperm combine inside of an organism
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usually takes place in the female
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mammals, reptiles, birds, some amphibians and fish
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External fertilization
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takes place outside of an organism
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most amphibians and fish
Gas Exchange (Respiration)
All animals need oxygen to survive. There are a few methods animals can use to obtain oxygen. The
main methods of gaining oxygen are as follows:
1. Integumentary exchange - gases diffuse across the skin or body covering. This is used by
flatworms, earthworms, and amphibians.
2. Tracheal respiration - animals with hard coatings have small holes in their body covering.
An empty tube runs through the body covering and into the tissue that needs the oxygen.
Oxygen passes through the tube and is absorbed into the tissue. Carbon dioxide is released from
the tissue and passes back out of the tube. This is used by spiders and some insects.
3. Internal gills - internal gills are at the back of the mouth and allow gas exchange between
water and blood vessels. Internal gills are used by fish.
4. External gills - external gills project out of the animal and into the water. External gills are
used by some insects and some amphibians.
5. Lungs - a lung is an internal respiratory surface in the shape of a sac or cavity. Oxygen from
the air is absorbed into blood vessels, and carbon dioxide from blood vessels is released into the
air. Lungs are used by mammals, birds, and reptiles. Some fish and amphibians also use lungs
as well as other methods.
Body Plan
Animals have different body plans that relate to how they live. Similarity in body plans is usually a
sign that organisms are related. Some examples of body plans include:
•
Asymmetry—Asymmetry means that an organism does not have
symmetry. Asymmetric bodies do not have regular, predictable
shapes, and it is not possible to cut through a central axis to create
similar left and right halves. This is the simplest type of body plan.
The sea sponge above has an irregular body and its left and right
sides are not similar. This is a classic example of asymmetry.
•
Radial Symmetry—Radial symmetry is a type of symmetry in
which several planes divide an organism into almost identical parts.
Organisms with radial symmetry have no "left" or "right" sides, but
they do have a "top" and a "bottom". Radially symmetric objects have
more than one line of symmetry.
The starfish above has five lines of symmetry. Since more than one
line of symmetry exists, the starfish is radially symmetrical.
•
Bilateral Symmetry—Bilateral symmetry is a kind of symmetry in
which a single plane divides an object into halves that are roughly
mirror images of each other.
The red line indicates a line of symmetry. The parts on either side of the
line are roughly identical.
Bilateral symmetry is an adaptation for locomotion. Organisms with
asymmetry or radial symmetry either move very slowly or do not move at all for most of their
lives. One of the most important features to develop as part of bilateral symmetry is the head.
The head is the result of nervous tissue and sensory organs that are concentrated on the end of
the organism that faces the direction of locomotion. This development gave organisms a chance
to sense the environment towards which they were moving. This is advantageous to find food
and avoid predators.
Digestion
All living things require energy to grow, develop, and reproduce. Animals accomplish this by
consuming other organisms. However, the organisms consumed must to be broken down to access
the raw materials.
In simple animals, such as sponges, digestion takes place within individual cells. Sponges do not
possess true tissues or organs. So, digestion takes place at the cellular level.
Other organisms have what is called an incomplete digestive system. It is also referred to as a twoway digestive tract. Organisms with incomplete digestive systems have a single opening through
which food enters; wastes are expelled from the same opening. Jellyfish and flatworms display this
type of digestive system.
Most animals possess a complete digestive system, or a one-way digestive tract. These animals
have a separate opening for food, the mouth, and wastes are expelled through the anus. So, food
travels in one direction and does not mix with wastes. Vertebrates, insects, and mollusks have
complete digestive systems.
Circulation
As organisms become larger and more complex, they require a system of transferring gases and
nutrients to all parts of the body. The circulatory system is responsible for this function in animals.
The simplest is an open circulatory system. Insects have open circulatory systems. Blood and body
fluid mix to form a substance called haemolymph. Since this system is not very efficient, the size of
these organisms is limited.
Closed circulatory systems are the most efficient at transporting nutrients and gases to all parts of the
body. Earthworms are the simplest animals with a closed circulatory system. They possess one
dorsal and one ventral blood vessel. Aortic arches are portions of the vessels that act like hearts by
pumping the blood. Unlike insects and other organisms with an open circulatory system, the blood
does not mix with other body fluids.
All vertebrates have closed circulatory systems with true hearts. Fish have the simplest heart. It
contains two chambers: an atrium, through which blood enters the heart, and a ventricle, through
which the blood exits to the aorta.
The vertebrate heart continued to evolve to become more efficient. New chambers that helped
separate nutrient-rich and nutrient-poor blood evolved.