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Chapter 19
The Animal
Kingdom
2
What Is an Animal?
Multicellular heterotrophs
Lack a cell wall
Motile during some stage in life
Able to respond rapidly to external stimuli
Able to reproduce sexually
Animal Evolution
Most animal phyla currently populating
the Earth were present by the
Cambrian period (544 million years ago)
The scarcity of pre-Cambrian fossils led
systematists to search for clues about
the evolutionary history of animals by
examining features of
• Anatomy
• Embryological development
• DNA sequences
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Animal Evolution
Certain features represent evolutionary
milestones
• The appearance of tissues
• The appearance of body symmetry
• Protostome and deuterostome
development
These features mark major branching
points on the animal evolutionary tree
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The Appearance of Body Symmetry
Symmetrical animals have an upper
(dorsal) surface and a lower (ventral)
surface
Animals with tissues exhibit either radial
or bilateral symmetry
Animals with radial symmetry can be
divided into roughly equal halves by
any plane that passes through the
central axis
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Body Symmetry and Cephalization
(a) Radial Central Axis
Symmetry
Another Radial Plane
A Radial Plane
Sagittal Plane
Anterior
Posterior
(b) Bilateral
Symmetry
Body Cavities
Acoelomate animals lack a body cavity
• e.g. flatworms
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Body Cavities:
The Acoelomates
Cnidaria
Digestive
Cavity
Digestive
Lining
Solid
Tissue
Body
Wall
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No cavity between
body wall &
digestive tract
Body Cavities
Pseudocoelomate animals possess a
pseudocoelom (a fluid-filled body cavity
that is not completely lined with
mesoderm)
• e.g. nematodes (roundworms)
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Body Cavities:
The Pseudocoelomates
Nematoda
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Body cavity
partially lined with
mesoderm
Digestive Cavity
Digestive Tract
Pseudocoelom
Partial Lining
Body Wall
Body Cavities
Coelomate animals possess a coelom (a
fluid-filled body cavity that is
completely lined with mesoderm)
• e.g. annelids, arthropods, mollusks,
echinoderms, chordates
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Body Cavities:
The True Coelomates
Annelida
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Body cavity
completely lined
with mesoderm
Digestive Cavity
Digestive Tract
Coelom
Complete Lining
Body Wall
Embryological Development
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Bilateral animals can be divided into two main
groups based on embryological development
Protostomes
• Body cavity forms within a space between the
body wall and the digestive cavity
• e.g. nematodes, arthropods, flatworms, annelids,
mollusks
Deuterostomes
• Body cavity forms as an outgrowth of the
digestive cavity
• e.g. echinoderms, chordates
Chapter 22
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Deuterostome
development
No true
tissues
True
tissues
No body
cavity
Protostome
development
Coelom
Pseudocoel
Body cavity
3 tissue
layers; bilateral
symmetry
2 tissue
layers; radial
symmetry
Evolutionary Tree
of Major Animal Phyla
The Invertebrate Phyla:
Porifera
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Phylum Porifera: the sponges
• Simple single-celled organisms living together
• Low specialization of cells; no tissue level
• Asymmetrical ::::: Reproduce by budding
Three major types of cells
• Epithelial cells (cover outer body surface)
– Some are modified into pore cells (regulate flow of water
through pores)
• Collar cells (flagellated cells that maintain water
flow through the sponge)
• Amoeboid cells (motile cells that digest and
distribute nutrients, produce reproductive cells, and
secrete spicules)
Epithelial
Cell
Spicules
Amoeboid
Cells
Pore
Cell
Collar
Cell
Osculum
Pore
Water Flow
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The Body
Plan of
Sponges
Chapter 22
The Invertebrate Phyla: Cnidaria
Phylum Cnidaria: the hydra, anemones, &
jellyfish – Radial symmetry
• Cells organized into distinct tissues
• Rudimentary nerve network and contractile
tissue
• No true organs
• Two distinct body plans:
– Polyp, attached
– Medusa, free swimming
• One digestive opening
• Reproduce sexually and asexually
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Cnidarian Body:
The Polyp
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Mouth
Body
Wall
Mesoglea
Tentacle
Column
Gastrovascular
Lining
Foot
Gastrovascular
Cavity
Cnidarian Body:
The Medusa
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Body
Wall
Gastrovascular
Cavity
Tentacle
Mesoglea
Gastrovascular
Lining
Mouth
Cnidarian Weaponry:
The Cnidocyte
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Trigger
Filament
Nuclei
Armed
Cnidocyte
Spent
Cnidocyt
Body
Wall
Water
The Invertebrate Phyla:
Platyhelminthes
The flatworms
• Development of bilateral symmetry
• Ability to move forward using aggregations
of nerve cells, ganglia
• True organs begin to evolve
• Most are hermaphroditic (can self-fertilize)
• Many are free living—planarians
• Some are parasitic—tapeworm and fluke
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Flatworm Organ Systems
Pharynx
(a) Digestive System
Excretory Canal
(b1) Excretory System
(b2) Nervous System
Nerve Cord
Gastrovascula
r
Cavity
Excretory Pore
Brain
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Chapter
Life 22
Cycle
Egg-filled
Human
eats
poorly
Larval
segments
aretapeworm
Tapeworm
matures in of
cooked
pork
with
liberated
by
digestion
shed from
worm
intestine,
live
cysts.
Head
withtohuman
hooks
&
attaches
human
& passed in& suckers
producing a series of Human
Larvae
through segments.
humanintestine.
feces. migrate
reproductive
vessels to pig muscles &
Pork
encyst
there.
Adult
tapeworm
Tapeworm
Larvae hatch
in pig intestine
Measly pork marketed for
Pig eats food
human consumption.
contaminated by
infected feces
The Invertebrate Phyla:
Nematoda (Round Worms)
Advanced gastrovascular cavity (are
bilateral)
• Tubular
• Two openings
Advanced sensory "ganglionic brain"
Lack circulatory and respiratory systems
Depend on diffusion for gas exchange
Sexual reprouction
Most are harmless - Some parasitic
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Heartworms in the
Heart of a Dog
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Open heart
of dog
Female
heartworms
The Invertebrate Phyla:
Annelida (Segmented Worms)
Bilateral symm.
Repeating rings identical nerve ganglia
Excretory structures
Advanced locomotion ability
Fluid-filled body cavity—coelom; involved in
locomotion (hydrostatic skeleton)
Sexual Repro.
Some hermaphrodites
Closed circulatory system
Evolved many rudimentary organ systems
• Nervous, excretory, circulatory, muscular
• Compartmentalized digestive tract
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Coelom
Intestine
Ventral
Nerve
Cord
ChapterNephridia
22 27
An Annelid:
the Earthworm
Excretory
Pore
Coelo
m
Gizzard
Ventral
Brain Nerve Cord
Ventral
Mouth Pharynx Vessel Hearts Esophagus Crop
Anus
Intestine
The Invertebrate Phyla:
Arthropoda
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The most numerous in numbers & species
Evolutionary adaptations allow them to reside in
diverse environments
• Paired, Jointed legs
• Exoskeleton for water conservation and support
• Segmentation
• Well-developed sensory and nervous systems
• Efficient gas-exchange (gills, trachea, book lungs)
• Well-developed (open) circulatory systems
• Sense organs – compound eyes
Reside in both aquatic and terrestrial habitats
Major Arthropod Classes:
Insecta
800,000 species
Have three pairs of legs
• Usually two pairs of wings
• Make escape from predators easier
Metamorphosis eliminates competition for
food between generations
The importance of insects
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Major Arthropod Classes:
Arachnida
50,000 species
• Spiders
• Mites
• Ticks
• Scorpions
Eight walking legs
Carnivorous
Simple eyes with a single lens
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Major Arthropod Classes:
Crustacea
30,000 aquatic species
• Crabs
• Crayfish
• Lobster
• Shrimp
• Barnacles
Size varies from microscopic to 12 feet (3.7 m)
Vary in number of appendages
Have two pairs of antennae
Generally with compound eyes
Exchange gases using gills
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Insect Body Plan
Abdomen
Thorax
Head
Antennae
Compound
Eyes
Wing
Mouth
Parts
The Invertebrate Phyla:
Mollusca (Snails & Clams)
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Bilateral Symmetry Coelomate
Moist muscular body without a skeleton
Found in aquatic or moist terrestrial habitats
Body protected by limy shell or obnoxious taste
Complex, concentrated, ganglionic brain
Open circulatory system
Classes
• Gastropoda—snails and sea slugs
• Pelecypoda— scallops, oysters, mussels, & clams
• Cephalopoda—octopuses, squid, nautiluses
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A Generalized Mollusk
Tentacle
Eye
Ganglia Digestive Tract
(brain)
Gonad Heart Coelom
Shell
Mantle
Anus
Foot
Radula
Mouth
Gill
Nerve Cords
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The Invertebrate Phyla:
Echinodermata (Sea Stars, Urchins)
Bilateral as larvae – Radial as adult
Deuterostome development
Coelomate
Possesses an endoskeleton of CaCO3
Lack a head and circulatory system
Simple nervous system; no distinct brain
Water-vascular system for slow movement
Can regenerate lost parts
Water-Vascular
System of Echinoderms
Sieve Plate
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Ampulla
Canals
Plates of
Endoskeleton
Photo (ventral)
A Mussel
(clam)
Tube Feet
Key Features of Chordates
Notochord
• Stiff flexible rod extending the length of
the body
Dorsal, hollow nerve cord
• Expands anteriorly to form brain
Pharyngeal gill slits
• May form respiratory organs or may
appear as grooves
Post-anal tail
• Extends past the anus
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Are Humans Chordates?
Only one chordate characteristic, the
nerve cord, is present in adult humans;
however, human embryos exhibit all
four…
• Tail will disappear completely
• Notochord is replaced by the backbone
• Gill slits (grooves) contribute to the
formation of the lower jaw
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Chapter 22
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The Vertebrates:
Chordata, Vertebrata
Subphyla
• Invertebrates—lancelets and tunicates
– Lack a head and backbone
– marine habitat
• Vertebrates
– Only 2.5% of extant animals
– Backbone
– Seven Major Classes
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The Lancelet:
An Invertebrate Chordate
Nerve Cord
Notochord
Gill Slits
Mouth
Gut
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Muscle
Segments
Tail
Anus
The Tunicate:
An Invertebrate Chordate
Brain
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Mouth
Water
Exit
ADULT
Gill
Slits
LARVA
Heart
Gut
Nerve Cord
Notochord
The Vertebrate Classes:
Agnatha & Chondrichthyes
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Agnatha—jawless fish
• Skeleton of cartilage and eellike shape
• Unpaired fins, lack scales
• Slimy skin perforated by circular gill openings
Chondrichthyes
• “Cartilaginous fishes”—sharks, skates, & rays
• Leathery skin
• Respire by gills
• Two-chamber heart
A Hagfish
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Lobe-Finned Fishes
Lungfish are found in freshwater
habitats
Have both gills and lungs
Tend to live in stagnant waters low in
oxygen
Lungs allow them to supplement their
supply of oxygen by breathing air
directly
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Lobe-Finned Fishes
Some species can survive even if the
water dries up
• Burrow into mud, Seal themselves in a
mucous-lined chamber and breathe
through lungs as metabolic rate slows,
Resume underwater life when rains
return and pool refills
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The Vertebrate Classes:
Osteichthyes
“Bony fishes”
Varied forms
Supplemental lungs for freshwater living
Fleshy fins
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The Vertebrate Classes:
Amphibia
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Bony support for the body
Waterproofing for the skin and eggs
Moist protection of respiratory membranes
Development of adult lungs
Cold Blooded --- External Fertilization
Still need aquatic habitat for reproduction
3 chambered heart
Amphibians Live a
Double Life
Include frogs, toads, and salamanders
“Double life” of amphibians
• Begin life adapted to aquatic
environment (eg tadpoles have gills)
• Mature into semiterrestrial adult with
lungs
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The Vertebrate Classes:
Reptilia
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Turtles, alligators, crocodiles, dinosaurs, birds
Respire through Lungs
Internal fertilization
Shelled amniotic egg (encapsulates embryo in a
liquid filled membrane, the amnion)
Skeleton modified for better support and
locomotion
Birds
Appeared in the fossil record about 150
million years ago
Considered by modern systematists to
be feathered reptiles
• The earliest known bird, Archaeopteryx
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Birds
Distinctive group of “reptiles” adapted for
flight
• Feathers (provide lift and control as well as
insulation)
• Hollow bones (reduce weight of skeleton)
• Females have a single ovary
• Shelled egg (frees female from carrying
developing offspring)
Maintain a constant body temperature
(warm-blooded)
The Vertebrate Classes:
Mammalia
Warm-blooded
Four-chambered heart
Fur for insulation and protection
Legs for running fast to avoid predators
Mammary glands to nurse live-born young
Complex cerebral cortex—increased learning
ability
Includes
• Egg-laying monotremes (platypus)
• Marsupials (opossums, koalas, kangaroos)
• Placental mammals (most other mammals)
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Mammals
Appeared in the fossil record about 250
million years ago
Did not diversify and dominate
terrestrial habitats until the dinosaurs
became extinct (65 million years ago)
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Bats,
the Only Flying Mammals
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Chapter 22
The End