The Animal Kingdom:
An Introduction to Animal
Diversity
Chapter 29
Learning Objective 1
•
What characters are common to most
animals?
Kingdom Animalia
•
•
•
•
Eukaryotic
Multicellular
Heterotrophic
Cells specialized for specific functions
Structure
•
Body plan
•
•
basic structure and functional design of body
Animals have diverse body plans
Function
•
Most animals
•
•
•
are capable of locomotion at some time
during life cycle
can respond adaptively to external stimuli
can reproduce sexually
Sexual Reproduction
•
Sperm and egg unite (zygote)
•
Zygote undergoes cleavage
•
cell divisions produce hollow ball of cells
(blastula)
•
•
Blastula undergoes gastrulation
•
forms embryonic tissues
KEY CONCEPTS
•
Animals are multicellular, eukaryotic
heterotrophs
Explore the characteristics of
animals by clicking on the
figures in ThomsonNOW.
Learning Objective 2
•
Compare the advantages and
disadvantages of life in the ocean, in fresh
water, and on land
Marine Environments
•
Provide
•
•
•
•
Fluid and salt balance
•
•
relatively stable temperatures
buoyancy
readily available food
more easily maintained than in fresh water
Disadvantages:
•
currents and other water movements
Fresh Water
•
Provides
•
•
•
less constant environment
less food
Animals must osmoregulate
•
fresh water is hypotonic to tissue fluid
Terrestrial Animals
•
Have adaptations that
•
•
•
protect them from drying out
protect them from temperature changes
protect their gametes and embryos
Marine and Terrestrial
Environments
Learning Objective 3
•
Use current hypotheses to trace the early
evolution of animals
Hypotheses
•
Proterozoic eon
•
•
•
most animal clades diverged over long period
based on molecular data
Cambrian Radiation
•
•
new body plans rapidly evolved among clades
first fossils of these animals
Hox Genes
•
Hox gene group
•
•
controls early development in animal groups
Cambrian period
•
•
many Hox genes had evolved
mutations could have resulted in rapid
changes in animal body plans
Learning Objective 4
•
How do biologists use structural
characters (variations in body symmetry,
number of tissue layers, type of body
cavity) and patterns of early development
to infer relationships among animal phyla?
Symmetry
•
Cnidarians and ctenophores are closely
related
•
•
•
because they share radial symmetry
most other animals exhibit bilateral symmetry
Cephalization (development of head)
•
evolved with bilateral symmetry
Radial and Bilateral Symmetry
Radial symmetry (top view)
Fig. 29-3a, p. 623
Radial symmetry (side view)
Fig. 29-3b, p. 623
Dorsal
Frontal
section
Caudal
Posterior
Anterior
Cephalic
Ventral
Cross (or transverse) section
Bilateral symmetry (lateral view)
Fig. 29-3c, p. 623
Dorsal
Sagittal section
Medial
Frontal
section
Lateral
Ventral
Bilateral symmetry (front view)
Fig. 29-3d, p. 623
Insert “Types of body
symmetry”
symmetry.swf
Other Structural Characters
•
Relationships can be based on
•
•
•
level of tissue development
type of body cavity
Embryonic tissues (germ layers)
Coelom Formation
Schizocoely —
characteristic of
protostomes
Enterocoely —
characteristic of
deuterostomes
Ectoderm
Developing
mesoderm
Blastopore
Ectoderm
Presumptive
mesoderm
Enterocoelic pouch
Endoderm
Mesoderm
Ectoderm
Developing coelom
(Schizocoel)
Ectoderm
Endoderm
Gut
Ectoderm
Endoderm
Mesoderm
Gut
Gut
Coelom
(Enterocoel)
Coelom
Mesoderm
Gut
Endoderm
Mesentery
Epidermis (ectoderm)
Coelom
Muscle layer
(mesoderm)
Gut
Peritoneum
(mesoderm)
Fig. 29-6, p. 626
Schizocoely —
characteristic of
protostomes
Enterocoely —
characteristic of
deuterostomes
Ectoderm
Developing
mesoderm
Blastopore
Ectoderm
Presumptive
mesoderm
Enterocoelic pouch
Endoderm
Mesoderm
Ectoderm
Ectoderm
Endoderm
Gut
Ectoderm
Endoderm
Developing coelom
(Schizocoel)
Mesoderm
Coelom
(Enterocoel)
Gut
Coelom
Mesoderm
Gut
Endoderm
Mesentery
Epidermis (ectoderm)
Coelom
Muscle layer
(mesoderm)
Peritoneum
(mesoderm)
Gut
Stepped Art
Fig. 29-6, p. 626
Germ Layers
•
Outer layer (ectoderm)
•
•
Inner layer (endoderm)
•
•
gives rise to body covering, nervous system
lines the gut and other digestive organs
Middle layer (mesoderm)
•
gives rise to most other body structures
Body Plans
Epidermis
(from ectoderm)
Muscle layer
(from
mesoderm)
Mesenchyme
(gelatin-like
tissue)
Epithelium (from
endoderm)
(a) Acoelomate—flatworm (liver fluke).
Fig. 29-4a, p. 624
Pseudocoelom
Epidermis
(from ectoderm)
Muscle layer
(from mesoderm)
Epithelium
(from endoderm)
(b) Pseudocoelomate—nematode.
Fig. 29-4b, p. 624
Coelom
Epidermis
(from ectoderm)
Muscle layer
(from mesoderm)
Peritoneum
(from mesoderm)
Epithelium
(from endoderm)
Mesentery
(from mesoderm)
(c) True coelomate—vertebrate.
Fig. 29-4c, p. 624
Insert “Types of body
cavities”
coelom.swf
Bilateral Symmetry
•
Acoelomate
•
•
Pseudocoelomate
•
•
no body cavity
body cavity not completely lined with
mesoderm
Coelomate, (animal with true coelom)
•
body cavity completely lined with mesoderm
Bilateral Animals
•
Two major evolutionary branches:
•
Protostomia
•
•
mollusks, annelids, arthropods
Deuterostomia
•
echinoderms, chordates
Blastopore
•
Opening from embryonic gut to outside
•
In protostomes
•
•
develops into the mouth
In deuterostomes
•
becomes the anus
Cleavage 1
•
Protostomes
•
•
•
undergo spiral cleavage
early cell divisions diagonal to polar axis
Deuterostomes
•
•
•
undergo radial cleavage
early cell divisions either parallel or at right
angles to polar axis
cells lie directly above or below one another
Spiral and Radial Cleavage
Polar axis
Top view
Spiral cleavage
Fig. 29-5a, p. 625
Top view
Polar axis
Radial cleavage
Fig. 29-5b, p. 625
Cleavage 2
•
Protostomes
•
•
•
undergo determinate cleavage
fate of each embryonic cell is fixed very early
Deuterostomes
•
•
undergo indeterminate cleavage
fate of each embryonic cell is more flexible
Relationships Based on Structure
Parazoa
Eumetazoa
Bilateria
Echinodermata
Coelomates
Chordata
Hemichordata
Annelida
Mollusca
Deuterostomia
Arthropoda
Onychophora
Tardigrada
Rotifera
Nematoda
Nemertea
Platyhelminthes
Ctenophora
Cnidaria
Acoelomates Pseudocoelomates
Protostomia
Porifera
Choanoflagellates
Radiata
Segmentation
Segmentation
Pseudocoelom
Deuterostome
development
True coelom
Radial
symmetry
Protostome development
Three tissue layers (mesoderm)
Bilateral symmetry
Tissues (ectoderm and endoderm)
Multicellularity
Choanoflagellate
ancestor
Fig. 29-7, p. 627
KEY CONCEPTS
•
Biologists classify animals based on their
body plan and features of their early
development
Learning Objective 5
•
What are three major contributions to
animal phylogeny made by molecular
systematics?
•
Identify the three major clades of bilateral
animals
Molecular Systematics 1
•
Confirmed much of animal phylogeny
based on structural characters
•
including axiom that animal body plans
usually evolved from simple to complex
Molecular Systematics 2
•
Provided evidence for exceptions to
“simple-to-complex” rule
•
Example
•
molecular data indicate flatworms and ribbon
worms evolved from more complex animals,
became simpler over time
Molecular Systematics 3
•
Molecular data suggest pseudocoelomate
animals do not form natural group
•
probably evolved from coelomate ancestors
Protostomes
•
2 clades based on molecular data:
•
Lophotrochozoa
•
•
flatworms, ribbon worms, mollusks, annelids,
lophophorate phyla, rotifers
Ecdysozoa (animals that molt)
•
nematodes and arthropods
3 Clades of Bilateral Animals
Lophotrochozoa
•
•
•
Ecdysozoa
Deuterostomia
Relationships
Based on
Molecular Data
Parazoa
Eumetazoa
Bilateria
Chordata
Hemichordata
Arthropoda
Onychophora
Tardigrada
Nematoda
Rotifera
Lophophorate
phyla
Annelida
Mollusca
Nemertea
Platyhelminthes
Ctenophora
Cnidaria
Ecdysozoa
Lophotrochozoa
Echinodermata
Deuterostomia
Protostomia
Porifera
Choanoflagellates
Radiata
Segmentation
Segmentation
Segmentation
Protostome
pattern of
development
Radial
symmetry
Deuterostome
pattern of development
Bilateral symmetry, three
tissue layers, body cavity
Tissues
Multicellularity
Choanoflagellate
ancestor
Fig. 29-8a, p. 629
Choanoflagellate
ancestor
Fig. 29-8b, p. 629
Deuterostomia
Ecdysozoa
Lophotrochozoa
Radiata
Parazoa
KEY CONCEPTS
•
Molecular data indicate that bilateral
animals split into three major clades:
•
two protostome groups—Lophotrochozoa
(such as flatworms, mollusks, and annelids)
and Ecdysozoa (such as nematodes and
arthropods)—and deuterostomes
(echinoderms and chordates)
Learning Objective 6
•
What are the distinguishing characteristics
of phylum Porifera?
Phylum Porifera
•
Sponges
•
•
animals characterized by flagellate collar cells
(choanocytes)
The only members of the Parazoa
•
sister group of Eumetazoa
Sponge Structure
•
Sponge body
•
•
•
•
sac with tiny openings for water to enter
central cavity (spongocoel)
open end (osculum) for water to exit
Sponge cells
•
•
loosely associated
do not form true tissues
Sponge Structure
Deuterostomia
Ecdysozoa
Lophotrochozoa
Radiata
Porifera
Parazoa
Choanoflagellate
ancestor
Fig. 29-9a, p. 630
Incurrent
pores
Water movement
Osculum
Spongocoel
Epidermal
cell
Porocyte
Spicule
Flagellum
Microvillus
Nucleus Collar cell Amoeboid cell
in mesohyl
Collar
Fig. 29-9b, p. 630
KEY CONCEPTS
•
Sponges (phylum Porifera) are
characterized by collar cells and by loosely
associated cells that do not form true
tissues
Insert “Body plan of a
sponge”
sponge_body.swf
Learn more about sponge
structure by clicking on the
figure in ThomsonNOW.
Learning Objective 7
•
What are the distinguishing characteristics
of phylum Cnidaria?
•
Describe four classes of this phylum
•
Give examples of animals that belong to
each class
Phylum Cnidaria 1
•
Characterized by
•
•
•
radial symmetry
two tissue layers
cnidocytes (cells containing nematocysts)
Nematocysts
Cnidocyte
Nucleus
Thread
Capsule
Nematocyst
(not discharged)
Cnidocil
(trigger)
Thread
Nematocyst
(discharged)
Fig. 29-11b, p. 634
Insert “Nematocyst
action”
nematocyst_v2.swf
Phylum Cnidaria 2
•
Gastrovascular cavity
•
•
with single opening for mouth and anus
Nerve cells form irregular, nondirectional
nerve nets
•
connect sensory cells with contractile and
gland cells
Cnidarian Structure
•
Hydra
Tentacles
Cnidocytes
(stinging
cells)
1 mm
Mouth
Bud
Gastrovascular
cavity
Epidermis
Mesoglea
Gastrodermis
Egg
(ovum)
Ovary
Fig. 29-12, p. 634
Cnidaria Life Cycle
•
Sessile polyp stage
•
•
form with dorsal mouth surrounded by
tentacles
Free-swimming medusa (jellyfish) stage
Cnidaria Life Cycle
•
Obelia
1 Reproductive polyps produce
medusae by budding asexually
Mouth
Tentacle
Medusae
Feeding
polyp
Medusa bud
Reproductive
polyp
Gastrovascular
cavity
Egg
2 Free-swimming
medusae
reproduce
sexually.
Sperm
Planula
larva
3 Zygote develops
into ciliated planula
larva.
Polyp colony
5 Colony grows as new polyps
bud and remain attached.
(b) Life cycle of Obelia.
Young
polyp colony
4 Larva develops into
polyp that forms new
colony.
Fig. 29-13b, p. 635
4 Classes of Phylum Cnidaria
1. Class Hydrozoa (hydras, hydroids,
Portuguese man-of-war)
•
•
typically polyps
may be solitary or colonial
2. Class Scyphozoa (jellyfish)
•
generally medusae
4 Classes of Phylum Cnidaria
3. Class Cubozoa (“box jellyfish”)
•
have complex eyes that form blurred images
4. Class Anthozoa (sea anemones, corals)
•
•
•
polyps
may be solitary or colonial
differ from hydrozoans in organization of
gastrovascular cavity
Cnidarians
Deuterostomia
Ecdysozoa
Lophotrochozoa
Ctenophora
Cnidaria
Parazoa
Radiata
Choanoflagellate
ancestor
Fig. 29-10 (1), p. 633
Mouth
Epidermis
Mesoglea
Gastrodermis
Gastrovascular
cavity
Class Hydrozoa (polyp)
Fig. 29-10a, p. 633
Mouth
Mesoglea
Gastrodermis
Epidermis
Gastrovascular
cavity
Class Scyphozoa (medusa)
Fig. 29-10b, p. 633
Mouth
Epidermis
Mesoglea
Gastrodermis
Gastrovascular
cavity
Class Anthozoa (polyp)
Fig. 29-10c, p. 633
Insert “Cnidarian body
plans”
cnidarian_bodies.swf
KEY CONCEPTS
•
Members of phylum Cnidaria (hydras,
jellyfish, sea anemones) are characterized
by radial symmetry, two tissue layers, and
cnidocytes, cells that contain stinging
organelles
Insert “Cnidarian life
cycle”
obelia_life_cycle.swf
Learn more about cnidarian body
forms, nematocysts, and life
cycles by clicking on the figures
in ThomsonNOW.
Learning Objective 8
•
What are the distinguishing characteristics
of phylum Ctenophora?
Phylum Ctenophora
•
Comb jellies
•
•
•
•
fragile, luminescent marine predators
biradial symmetry
eight rows of cilia that resemble combs
tentacles with adhesive glue cells
Comb Jelly
KEY CONCEPTS
•
Members of phylum Ctenophora (comb
jellies) have biradial symmetry, two tissue
layers, eight rows of cilia, and tentacles
with adhesive glue cells