Animals
Characteristics and
Classification
Segmented Worm
What is an animal?
Tree Frog
When you think of animals you probably think of a
variety of furry or hairy creatures, and possibly
some fish. But the animal kingdom encompasses a
wide variety of living things. A few examples are
shown here.
African Elephant
Caterpillar
Jelly Fish
What makes an animal?
We have to be able to separate animals from other
living things like plants and fungi. To do this scientist
look for key features. Can you pick out the animal?
Sea Sponge
Venus fly trap
All animals have at least one cell. For an organism to be
multicellular it must have more than 1 cell. Many animals
have trillions of cells. More cells generally means the
organism is more complex.
This is a picture of mouse cells under a
microscope that have been stained.
There are different types of cells, and
many animals have cells that perform
specialized functions.
All animals are heterotrophs. Heterotrophs must consume
other organic materials for their carbon sources. This means
animals must eat other living or once living organisms in
order to get the energy they need to survive. They also
usually have an internal chamber where they digest their
food.
Here you see a Giant Panda
eating. He must consume the
grass (a living organic material)
for energy. The food will pass into
the digestive tract, where it will be
broken down and the nutrients will
be absorbed.
Animals have cellular membranes.
Animals do not have cell walls.
Cell walls are cellular structures specific to plants, algae, and
fungi.
Plant Cells- notice that the
cells are all separated by
walls. Plants need cell walls
to protect their structure.
Animal cells do not have cell
walls. In fact many animal cells
contain specialized structures
that interconnect the cells.
Almost all animals have differentiated tissues. The simplest case is to
have muscle and nervous tissue. Muscle and nervous tissue are a
necessity because they allow an animal to move and respond to its
environment . Almost all animals are mobile. Even if it is only at one
stage of their life cycle.
This sea cucumber is using its
tiny tentacles to search the
ocean floor for plankton and
decaying organic material.
Both its muscular and nervous
system are very important for
it to survive and react to its
environment.
Most animals have some form of symmetry. In biology symmetry is
the balanced distribution of duplicate body parts or shapes. There are
two forms of symmetry, bilateral symmetry (which humans have) and
radial symmetry.
This butterfly is a good example of bilateral
symmetry. Its left side matches its right side in
two ways. The patterns on its wings are
bilaterally symmetrical, and so are its body parts.
It has a wing, an antenna, and an eye on each
side of its body. Think about your own body.
How are you bilaterally symmetrical?
Most animals who have symmetry have bilateral symmetry. This means
they will have only one plane of symmetry. You can only divide the
organism in one way to produce mirror images. Look at the example
below. It is obvious that the bear could only be divided one way to
produce mirror images.
Kodiak bear
Symmetrical
Mirror images
Not mirror images
Star fish
For an organism to have radial symmetry it
must not have a left or right side. It will only
have a top and a bottom and it could be cut
many ways to produce mirror images. Think of
a pie. If you start in the center and cut from
edge to edge you will always have two equal
sides. The starfish is considered to have radial
symmetry but it is somewhat superficial. The
jelly fish is a better example of radial
symmetry. Can you explain why?
Jelly fish
pie
Think back to the Sea sponge and Venus fly trap. Both of the organisms
consume other living organisms. The sponge filters water through its
body to pull out food particles. The Venus fly trap lures bugs onto its
palate and then snaps shut digesting the bugs with enzymes. Both are
stationary.
The sea sponge has a cellular membrane. The Venus fly trap has cell
walls. Neither organism has true muscular or nervous tissue. Given this
information which organism is an animal?
If you said the sea sponge you are correct. The sea sponge is an
example of the simplest animal. Things like reproduction, life cycle
and body composition are factors we did not discuss that scientist
considered when they classified the sea sponge as an animal.
Classification in the world of science is about “best fit.”
Other factors that classify the sea sponge as an
animal is its ability to reproduce sexually, they way it
digests its food, and the way it matures and develops
as it grows.
After determining an organism is an animal, scientist study its features
and group it together with other animals that it is most similar to.
Classification is based on internal structures and processes and
on external characteristics.
Least Weasel
Elephant Seal
Polar Bear
All of these animals
belong to the same
Order. They may not look
alike but they have many
similarities that may not
be obvious at first glance.
Leopard
Pinniped
The Diagram at the right is a representation of
the way living things are classified. As you move
from kingdom towards species each group contains
organisms with more things in common than the
one before it.
Another way to think of it is that there are fewer
members in a common Family than there are in a
common Order.
Dog
Cat
Phylum: Chordata
Class:
Mammalia
Order: Carnivora
Family: Canidae
Genus: Canis
Species:Canis lupus
Phylum:Chrodata
Class: Mammalia
Order: Carnivora
Family: Felidae
Genus: Felis
Species:Felis catus
A dog and a cat belong to the same Phylum, Class, and Order. They
are both in the Phylum Chordata because they both have vertebral
columns. They are both in the Class Mammalia because they have hair,
mammary glands, and a specialized ear bone. They are both in the
Order Carnivora because they both are meat eating mammals.
When identifying an organism by its scientific name we use only the
Genus and Species name. This is called binomial nomenclature. The
Genus name is capitalized and the species name is lowercase. It is
proper to either underline or italicize both of the names. See the
examples below.
Common name: Tiger
Common Name: Roman snail
Scientific Name: Panthera tigris
Scientific Name: Helix pomatia
Practice naming these animals with binomial
nomenclature.
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Artiodactyla
Family: Suidae
Genus: Sus
Species: barbatus
Species Name: Sus barbatus
Kingdom: Animalia
Phylum: Mollusca
Class: Cephalopoda
Order: Teuthida
Family: Loliginidae
Genus: Loligo
Species: vulgaris
Species Name: Loligo vulgaris
References
www.photokonkurs.com
www.flickr.com
www.wikipedia.com
http://ngm.nationalgeographic.com/
www.yahooimages.com
www.images.fws.gov
http://animaldiversity.ummz.umich.edu/site/index.html