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Chapter 24 Introduction to Animals
Section 1: Animal Characteristics
Section 2: Animal Body Plans
Section 3: Sponges and Cnidarians
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Chapter 24 Introduction to Animals
24.1 Animal Characteristics
 The ancestral animals
General Animal Features
at the beginning of the
evolutionary tree are
eukaryotic and
multicellular.
 They developed
adaptations in
structure that enabled
them to function in
numerous habitats.
Chapter 24 Introduction to Animals
24.1 Animal Characteristics
Feeding and Digestion
 Animals are
heterotrophic.
 The structure or
form of an animal’s
mouth parts
determines how its
mouth functions.
Chapter 24 Introduction to Animals
24.1 Animal Characteristics
Support
 Invertebrates
Any animal without
a backbone.
95-99% of animal
species are
invertebrates
The bodies of most
are covered by
exoskeletons.
Chapter 24 Introduction to Animals
24.1 Animal Characteristics
Support
 Exoskeletons
 Hard or tough outer
coverings that provide
a framework of
support
 Protect soft body
tissues
 Provide protection
from predators
Chapter 24 Introduction to Animals
24.1 Animal Characteristics
Support
 Vertebrates
Have an
endoskeleton and
a backbone
Chapter 24 Introduction to Animals
24.1 Animal Characteristics
Support
 Endoskeletons
Protect internal
organs
Provide support for
the body
Provide an internal
brace for muscles to
pull against
Chapter 24 Introduction to Animals
24.1 Animal Characteristics
Movement
 The evolution of
nerve and muscle
tissues enables
animals to move in
ways that are
more complex and
faster than
organisms in other
kingdoms.
Chapter 24 Introduction to Animals
24.1 Animal Characteristics
Reproduction
 Most animals
reproduce sexually,
although some can
reproduce asexually.
 Some animals, such
as earthworms, are
hermaphrodites,
producing eggs and
sperm in the same
body.
Chapter 24 Introduction to Animals
24.1 Animal Characteristics
Sexual Reproduction
 Fertilization occurs
when the sperm
penetrates the egg
to form a fertilized
egg cell called the
zygote.
 Fertilization can be
1) internal or 2)
external
Chapter 24 Introduction to Animals
24.1 Animal Characteristics
 Internal fertilization
The sperm and egg
combine in the animal’s
body.
 External fertilization
Occurs when egg and
sperm combine outside
the body.
Requires an aquatic
environment.
Chapter 24 Introduction to Animals
24.1 Animal Characteristics
 Asexual reproduction means that a single
parent produces offspring that are genetically
identical to itself.
 Budding
 Fragmentation
 Regeneration
 Parthenogenesis
Chapter 24 Introduction to Animals
24.1 Animal Characteristics
 Budding-Offspring
develop as a
growth on the body
of the parent
Chapter 24 Introduction to Animals
24.1 Animal Characteristics
 Fragmentation –
Parent breaks into
pieces and each
piece can develop
into an adult
organism.
Chapter 24 Introduction to Animals
24.1 Animal Characteristics
 Regeneration – A
new organism can
regenerate or
regrow from the
lost body part if the
part contains
enough genetic
information.
Chapter 24 Introduction to Animals
24.1 Animal Characteristics
 Parthenogenesis – A
female animal
produces eggs that
can develop without
being fertilized.
Chapter 24 Introduction to Animals
24.1 Animal Characteristics
Early Development
 The zygote
undergoes mitosis
and a series of cell
divisions to form
new cells.
 The cells continue
to divide, forming a
fluid-filled ball of
cells called the
blastula.
Chapter 24 Introduction to Animals
24.1 Animal Characteristics
Early Development
 The blastula
continues to
undergo cell
division as some
cells move inward
to form a gastrula.
Chapter 24 Introduction to Animals
24.1 Animal Characteristics
Chapter 24 Introduction to Animals
Chapter 24 Introduction to Animals
24.1 Animal Characteristics
Tissue Development
 Endoderm
inner layer of
cells in the
gastrula
Forms the
digestive organs
and digestive tract
lining.
Chapter 24 Introduction to Animals
24.1 Animal Characteristics
Tissue Development
 Ectoderm
 outer layer of
cells in the
gastrula
 Forms the
nervous tissue
and skin.
Chapter 24 Introduction to Animals
24.1 Animal Characteristics
Tissue Development
 Mesoderm
layer of cells
between the
endoderm and
ectoderm
Forms muscle
tissue,
circulatory,
excretory, and
respiratory
systems
Chapter 24 Introduction to Animals
24.1 Animal Characteristics
Chapter 24 Introduction to Animals
Animation
 Cell Differentiation in Animal
Development
 Visualizing Protostome and
Deuterostome Development
 A Sponge
 A Cnidarian
Chapter 24 Introduction to Animals