Chapter 24 Introduction to Animals
Section 1: Animal Characteristics
Section 2: Animal Body Plans
Click on a lesson name to select.
Chapter 24 Introduction to Animals
24.1 Animal Characteristics
Animal Features
 The ancestral
animals at the
beginning of the
evolutionary tree
are eukaryotic
and
multicellular.
Adaptive Radiation
• 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
 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
 Endoskeletons
 Protect internal organs
 Provide support for the body
 Provide an internal brace for muscles to
pull against
Chapter 24 Introduction to Animals
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
 Fertilization occurs when the sperm penetrates
the egg to form a fertilized egg cell called the
zygote.
 Internal fertilization
 External fertilization
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
Early Development
 The zygote undergoes mitosis and a series
of cell divisions to form new cells.
 The cells continue to divide, forming a fluidfilled ball of cells called the blastula.
 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
Cell Differentiation in
Animal Development
Chapter 24 Introduction to Animals
24.1 Animal Characteristics
Tissue Development
 Endoderm
 inner layer of cells in the gastrula
 Ectoderm
 outer layer of cells in the gastrula
 Mesoderm
 layer of cells between the endoderm
and ectoderm
Chapter 24 Introduction to Animals
24.1 Animal Characteristics
Chapter 24 Introduction to Animals
24.2 Animal Body Plans
Evolution of Animal Body Plans
 Anatomical features in animals’ body
plans mark the branching points on the
evolutionary tree.
 Relationships on this tree are inferred by
studying similarities in embryological
development and shared anatomical features.
Chapter 24 Introduction to Animals
24.2 Animal Body Plans
Chapter 24 Introduction to Animals
24.2 Animal Body Plans
Symmetry
 Similarity or balance among body structures of organisms
 Asymmetry
 Radial symmetry
 Bilateral symmetry
Chapter 24 Introduction to Animals
24.2 Animal Body Plans
Cephalization
 The tendency to
concentrate
nervous tissue
and sensory
organs at the
anterior end of
the animal
Chapter 24 Introduction to Animals
24.2 Animal Body Plans
Body Cavities
 Coelomates
 Have a fluidfilled cavity with
tissue formed
from mesoderm
that lines and encloses the organs in the
coelom
Chapter 24 Introduction to Animals
24.2 Animal Body Plans
Body Cavities
 Pseudocoelomates
 Have a fluid-filled
body cavity that
develops between
the mesoderm and
the endoderm rather than developing
entirely within the mesoderm
Chapter 24 Introduction to Animals
24.2 Animal Body Plans
Body Cavities
 Acoelomates
 Have solid bodies
without a fluid-filled
body cavity
between the gut
and the body wall
Chapter 24 Introduction to Animals
24.2 Animal Body Plans
Development in Coelomate Animals
 Protostomes
 The mouth develops from the first opening in
the gastrula.
 Deuterostomes
 The anus develops from the first opening in
the gastrula.
Visualizing
Protostomes and
Deuterostomes
Chapter 24 Introduction to Animals
24.2 Animal Body Plans
Segmentation
 Segmented animals can be “put together”
from a succession of similar parts.
 Can survive damage to one segment
 Movement is more effective
Segmentation!
Michel Angelo’s David