Typical Animal Characteristics

Chapter 25
What is an animal?
Sections 1 and 2
Typical Animal Characteristics
Body Plans and Adaptations
Section 1 –
Typical Animal Characteristics
Characteristics of All Animals:
All eukaryotic.
All multicellular organisms.
All have cells without cell walls.
All are heterotrophic.
Characteristics of All Animals:
All animals must digest their food
within individual cells or in an
internal cavity.
Some of the digested food is stored as
fat or glycogen to use as a source of
energy at a later time.
Characteristics of Some Animals:
Most have ways of moving that
help them reproduce, obtain food,
and protect themselves.
Most have specialized cells that form
tissues and organs.
Characteristics of Some Animals:
Some organisms are sessile:
Organisms that are permanently
attached to a surface.
Do not expend much energy to
obtain food.
Adult forms of coral and sponges.
Development of Animals
Most animals reproduce sexually.
Development of Animals
A zygote is formed when female egg
cells are fertilized by male sperm
Fertilization may be internal or external.
Development of Animals
The zygote divides through mitosis
to form two cells in a process called
Once cell division has begun the
zygote becomes an embryo.
Development of Animals
The two cells further divide by mitosis
into four cells, and so on, until a cellcovered fluid-filled ball called a
blastula is formed.
Development of Animals
After the formation of the blastula, cell
division continues.
The cells on one side of the blastula
move inward to form a structure
made up of two layers of cells with
an opening at one end called a
Development of Animals
The layer of cells on the outer
surface of the gastrula is called the
ectoderm and eventually develops
into skin and nervous tissue.
Development of Animals
The layer of cells on the inner
surface of the gastrula is called the
endoderm and eventually develops
into the digestive tract and organs
for digestion.
Development of Animals
In some animals the cells of the gastrula
further divide into a third layer called
the mesoderm, located between the
ectoderm and the endoderm.
The mesoderm eventually forms the
muscles, circulatory system, excretory
system, and sometimes the respiratory
Development of Animals
Protostomes vs. Deuterostomes
When the opening of the gastrula
develops into a mouth the animal
is called a protostome.
Examples: snails, earthworms, and
Development of Animals
Protostomes vs. Deuterostomes
When the mouth of the organism is
not developed from the opening
to the gastrula, the animal is called
a deuterostome.
Examples: sea stars, fish, toads,
snakes, birds, and humans.
Development of Animals
Cells in developing embryos
continue to differentiate and
become specialized to perform
different functions.
Development of Animals
Some embryos develop into
miniature forms of adults
called juveniles.
Development of Animals
Some embryos develop inside an
egg into an intermediate stage
called a larva which has little
resemblance to the adult.
Inside the egg, the larva is
surrounded by a membrane formed
right after fertilization.
Development of Animals
After the juvenile or larval stage the
animal passes into the adult stage
and cycle begins again.
Section 2 –
Body Plans and Adaptations
A term used to describe the
arrangement of body structures:
Radial Symmetry
Bilateral Symmetry
An animal that is irregular in
Asymmetrical animals are often
Example: Sponges
Radial Symmetry
Animals that can be divided along
any plane through a central axis
into roughly equal halves.
Radial symmetry enables an animal
to detect and capture prey coming
toward it from any direction.
Example: Hydra
Bilateral Symmetry
Animal can be divided down its
length into similar right and left
Bilateral Symmetry
Bilateral animals have four sides:
Anterior or head end (often with sensory
Posterior or tail end
Dorsal or upper surface
Ventral or lower surface
Bilateral Symmetry
All animals with bilateral symmetry
developed from three embryonic
cell layers – ectoderm, endoderm,
and mesoderm.
Bilateral Symmetry
Some animals with bilateral
symmetry also have fluid-filled
spaces inside their bodies in which
internal organs are found called body
These cavities allow the animal to grow
large because they provide efficient
circulation and transportation of fluids and
support for organs and organ systems.
Bilateral Symmetry
Animals with bilateral symmetry
can be divided into:
Bilateral Symmetry
Have no body cavities
Have digestive tracts that extend
throughout the body.
May have been the first group of animals in
which organs evolved.
The organs are embedded in the solid tissues
of the body.
Example: Flatworm
Bilateral Symmetry
Have a fluid-filled body cavity partly
lined with mesoderm that develops
between the endoderm and mesoderm
Have a one-way digestive tract that has
regions with specific functions.
Can move quickly because muscles attach
to the mesoderm and brace against the
rigid, fluid-filled psuedocoelom.
Examples: Roundworm
Bilateral Symmetry
Have a fluid-filled body cavity
completely surrounded by mesoderm
Have the greatest diversity of all animals.
Specialized organs and organ systems
develop in the coelom.
The digestive tract and other internal organs
are attached by double layers of mesoderm and
are suspended within the coelom, which
cushions and protects them.
Animal Protection and Support
Hard covering on the outside of the
body that:
Provides a framework for support
Protects soft body tissues
Prevents water loss
Provides protection from predators
Animal Protection and Support
The exoskeleton is secreted by the
epidermis and extends into the body
where it provides a place for muscle
As an animal grows it secretes a new
exoskeleton and sheds the old one.
Usually found in invertebrates which are
animals that do not have a backbone.
Examples: Crabs, spiders, dragonflies,
Animal Protection and Support
Covered by layers of cells
Provides support for the body
Protects internal organs
Provides an internal brace for
muscles to pull against
May be made of calcium carbonate,
cartilage, or bone.
Animal Protection and Support
May be found in invertebrates such
as sea stars and sea urchins or in
vertebrates, which are animals with
both an endoskeleton and a backbone,
such as fish, amphibians, reptiles,
birds, and mammals.
Origin of Animals
Probably evolved from aquatic,
colonial protists in the late
All the major body plans that exist
today were thought to already be in
existence by the beginning of the
Cambrian Period 543 million years