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
General Animal Features
 The ancestral animals 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
 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
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
 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
Chapter 24 Introduction to Animals
24.3 Sponges and Cnidarians
Sponges
 Sponges do not develop tissues.
 Collar cells with flagella line the inside of
the sponge and whip back and forth
drawing water into the body of the sponge.
 Water and waste materials are expelled
from the sponge through the osculum.
Chapter 24 Introduction to Animals
24.3 Sponges and Cnidarians
A Sponge
Chapter 24 Introduction to Animals
24.3 Sponges and Cnidarians
Filter Feeder
 Food particles cling to the cells.
 Digestion of nutrients takes place within
each cell.
Chapter 24 Introduction to Animals
24.3 Sponges and Cnidarians
Archaeocytes
 Specialized cells that secrete spicules, which
are the support structures of sponges
 Spicules are small, needlelike structures
made of calcium carbonate, silica, or a tough
fibrous protein called spongin
Chapter 24 Introduction to Animals
24.3 Sponges and Cnidarians
Sponge Diversity
 Demospongiae
 Calcarea
 Hexactinellida
Chapter 24 Introduction to Animals
24.3 Sponges and Cnidarians
Reproduction
 Reproduce asexually
 Fragmentation
 Budding
 Gemmules
 Reproduce sexually
 Eggs remain within a sponge.
 Sperm are released into the water.
Chapter 24 Introduction to Animals
24.3 Sponges and Cnidarians
Cnidarians
 Have one body opening and two layers
of cells
 Outer layer functions in protecting the
internal body
 Inner layer functions mainly in digestion
Chapter 24 Introduction to Animals
24.3 Sponges and Cnidarians
Feeding and Digestion
 Tentacles are armed with stinging cells called
cnidocytes.
 A nematocyst is a capsule that holds a coiled
tube containing poison and barbs.
 Water inside an undischarged nematocyst
is under an osmotic pressure of more than
150 atmospheres.
Chapter 24 Introduction to Animals
24.3 Sponges and Cnidarians
 As the osmotic
pressure increases,
the nematocyst
discharges forcefully.
 A barb is capable
of penetrating a
crab shell.
Chapter 24 Introduction to Animals
24.3 Sponges and Cnidarians
 Cells lining the
gastrovascular cavity
release digestive
enzymes over
captured prey.
 Undigested materials
are ejected though
the mouth.
Chapter 24 Introduction to Animals
24.3 Sponges and Cnidarians
Response to Stimuli
 A nerve net conducts impulses to and
from all parts of the body.
 The impulses cause contractions of
musclelike cells in the two cell layers.
Chapter 24 Introduction to Animals
24.3 Sponges and Cnidarians
Reproduction
 Two body forms
 Polyp
 Medusa
Chapter 24 Introduction to Animals
24.3 Sponges and Cnidarians
 The two body forms
of cnidarians can be
observed in the life
cycle of jellyfishes.
A Cnidarian
Chapter 24 Introduction to Animals
24.3 Sponges and Cnidarians
Cnidarian Diversity
 Hydroids
 Jellyfishes
 Sea anemones and corals
Comparison
of Sponges
and Cnidarians
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