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INTRODUCTION TO THE
ANIMAL KINGDOM
Biology 20
Which of these are animals?
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Answer:
They ALL are!
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Characteristics of Animals
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Multicellular
 Eukaryotic
 Heterotrophic
 Lack cell walls
 Evolved to live in many
different habitats
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ANIMAL FEATURES
Feeding
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All are heterotrophic and must digest their
food (and excrete waste too!)
Very diverse in how they eat, digest, and
excrete
Herbivore = eats plants
 Carnivore = eats animals
 Omnivore = eats plants and animals
 Detritivore = feed on decaying organic material
 Filter Feeders = aquatic animals that strain food from water
 Parasite = lives in or on another organism

Respiration and Circulation
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All take in oxygen and circulate it to their tissues
(and give off carbon dioxide!)
How they do this is very diverse: very small
animals rely on diffusion while larger animals
have a circulatory system
 Simple
diffusion
 Through skin
 Lungs
 Gills
Movement
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
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Most animals have a
body form that can
move at some stage in
its development
The evolution of nerve
and muscle tissue lets
animals move faster
than organisms in any
other kingdom
Support
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
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Animals support their bodies in different ways
95% of animals are invertebrates (without a
backbone)
 Many
are covered with exoskeleton (tough outer covering
that provides support and protects internal tissues)
 Some have internal skeletons called endoskeleton

5% of animals are vertebrates (with a backbone)
 Have
an endoskeleton made of calcium carbonate,
cartilage, bone
Sexual Reproduction
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
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Most animals reproduce sexually
Male animals produce sperm and female animals
produce eggs
Hermaphrodites produce both sperm and eggs in
the same body
Sexual Reproduction
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

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Fertilization occurs when the sperm penetrates the
egg to form a fertilized egg called the zygote
Internal fertilization occurs when the sperm and egg
combine inside the body
External fertilization occurs when the sperm and
egg combine outside the body (i.e. in water)
Asexual Reproduction
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
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To increase their populations
rapidly, some animals can
reproduce asexually
They do so using one or more
methods
 Budding
 Fragmentation
 Regeneration
(new growth from a
lost body part if the body part
contains enough genetic information)
Early Development
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
Animals begin life as a
zygote (fertilized egg)

The cells in the zygote
divide to form the
blastula - a hollow
ball of cells
Tissue Development
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
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The blastula pinches
inward to form three
germ layers. This stage
forms what is called the
gastrula.
Inner layer is the
endoderm which
develops into the
digestive organs and
tract
Gastrula
Tissue Development
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Outer layer is the
ectoderm which become
the nervous tissue and
skin
Middle layer is the
mesoderm which
develops into muscle
tissue and the
circulatory, excretory,
and respiratory systems
Body Plan
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
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Asymmetry - no pattern
(corals, sponges)
Radial Symmetry - shaped
like a wheel (starfish, hydra,
jellyfish)
Bilateral Symmetry - right
and left sides
(humans, insects, cats)
Identify the Symmetry
Body Plan
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Animals with bilateral symmetry
also have an anterior (head
end) and a posterior (tail end)
This body plan is called
cephalization - an anterior
concentration of sense organs
The more complex the animal
becomes the more pronounced
their cephalization
Body Plan
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
Animals with bilateral
symmetry also have a
dorsal surface
(backside) and a
ventral surface
(underside or belly)
Body Cavities
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Animals with bilateral symmetry have a gut, which is
a sac inside the body or a tube that runs through
the body, where food is digested
A sac-like gut has one opening – a mouth – for
taking in food and disposing of wastes
A tube-like gut has openings at both ends – mouth
and anus – and is a complete digestive system
Body Cavities
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Between the gut and the outside body wall of most
animals is a fluid-filled body cavity.
Two types:
 coelom
(SEE lum) is a fluid-filled body cavity completely
surrounded by mesoderm
 psuedocoelom is a fluid-filled cavity between the
mesoderm and endoderm
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An animal with a solid body that lacks a fluid-filled
body cavity is called an acoelomate.
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Segmentation
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Advanced animals
have body segments
Even humans are
segmented (look at the
ribs and spine)!
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TYPES OF ANIMALS &
EVOLUTIONARY MILESTONES
Phylum Porifera
(sponges) multicellularity
Phylum Cnidaria
(sea anemones,
jellyfish, hydra) tissues
Free-living Planarian
Parasitic Tapeworm
Phylum Platyhelminthes(flatworms) –
bilateral symmetry
Phylum Nematoda
(roundworms) pseudocoelom
Phylum Annelida
(segmented
worms) segmentation
Phylum Mollusca (clams, squid,
snails) - coelom
Phylum Arthropoda (crustaceans,
insects) – jointed appendages
This is the largest phylum in
the animal kingdom and
contains the most number of
species
Phylum Echinodermata (starfish) –
mouth and anus
Phylum Chordata
(vertebrates) – spinal cord