1. Which of these organisms are animals?
Figure 32.1 Which of these organisms are animals?

2. Animal Early Embryonic Development
Cleavage
Blastocoel
Endoderm
Blastula
Ectoderm
Archenteron
Zygote
Eight-cell stage
Gastrulation
Gastrula
Figure 32.2 Early embryonic development in animals
Blastocoel
Blastopore
Cross section
of blastula

3. Three lines of evidence that choanoflagellates protists are closely related to animals
Individual
choanoflagellate
Choanoflagellates
OTHER
EUKARYOTES
Sponges
Figure 32.3 Three lines of evidence that choanoflagellates are closely related to animals
Animals
Collar cell
(choanocyte)
Other animals

4. (a) Mawsonites spriggi (b) Spriggina floundersi
Early members of the animal fossil record include the Ediacaran biota, which dates from 565 to 550 million years ago
0.4 cm
1.5 cm
Figure 32.4 Ediacaran fossils
(a) Mawsonites spriggi
(b) Spriggina floundersi

5. A Cambrian seascape
Figure 32.5 A Cambrian seascape

6. Animal Body Symmetry (a) Radial symmetry (b) Bilateral symmetry
Figure 32.7 Body symmetry
(b) Bilateral symmetry

7. Triploblastic Animals Body Cavities
Coelom
Body covering
(from ectoderm)
Tissue layer lining coelom
and suspending internal organs
(from mesoderm)
Digestive tract
(from endoderm)
(a) Coelomate - true body cavity
Body covering
(from ectoderm)
Pseudocoelom
Muscle layer
(from
mesoderm)
Digestive tract
(from endoderm)
(b) Pseudocoelomate
Figure 32.8 Body cavities of triploblastic animals
Body covering
(from ectoderm)
Tissue-
filled region
(from
mesoderm)
Wall of digestive cavity
(from endoderm)
(c) Acoelomate - lack a body cavity

8. Protostome Deuterostome
Development
molluscs, annelids
Deuterostome
Development
echinoderm, chordates
(a) Cleavage
Eight-cell stage
Eight-cell stage
Spiral and determinate
Radial and indeterminate
Key
Coelom
Ectoderm
(b) Coelom formation
Mesoderm
Archenteron
Endoderm
Coelom
Mesoderm
Blastopore
Blastopore
Mesoderm
Folds of archenteron
form coelom.
Solid masses of mesoderm
split and form coelom.
Figure 32.9 A comparison of protostome and deuterostome development
Anus
Mouth
(c) Fate of the blastopore
Digestive tube
Mouth
Anus
Mouth develops from blastopore.
Anus develops from blastopore.

9. “Porifera”
Cnidaria
ANCESTRAL
COLONIAL
FLAGELLATE
Metazoa
Ctenophora
Eumetazoa
Ectoprocta
Brachiopoda
Deuterostomia
Echinodermata
Chordata
Bilateria
Platyhelminthes
Figure A view of animal phylogeny based mainly on morphological and developmental comparisons
Rotifera
Protostomia
A view of animal phylogeny based mainly on morphological and developmental comparisons
Mollusca
Annelida
Arthropoda
Nematoda

10. A view of animal phylogeny based mainly on molecular data
Silicea
“Porifera”
Calcarea
ANCESTRAL
COLONIAL
FLAGELLATE
Metazoa
Ctenophora
Cnidaria
Eumetazoa
Acoela
Echinodermata
Deuterostomia
Chordata
Bilateria
Platyhelminthes
Rotifera
Ectoprocta
Figure A view of animal phylogeny based mainly on molecular data
Lophotrochozoa
Brachiopoda
A view of animal phylogeny based mainly on molecular data
Mollusca
Annelida
Nematoda
Ecdysozoa
Arthropoda

11. Ecdysis - Shedding of Exoskeleton
Figure Ecdysis

12. Lophotrochozoans Characteristics
Lophophore
Apical tuft
of cilia
Mouth
Figure Morphological characteristics found among lophotrochozoans
100 µm
Anus
(a) An ectoproct
(b) Structure of a trochophore
larva

13. Common ancestor of all animals Sponges (basal animals) Ctenophora
Animal Phylogeny
Common ancestor
of all animals
Sponges
(basal animals)
Metazoa
Ctenophora
Eumetazoa
Cnidaria
True
tissues
Acoela (basal
bilaterians)
Deuterostomia
Bilateria (most animals)
Bilateral
summetry
Lophotrochozoa
Three germ
layers
Ecdysozoa

14. You should now be able to:
List the characteristics that combine to define animals.
Summarize key events of the Paleozoic, Mesozoic, and Cenozoic eras.
Distinguish between the following pairs or sets of terms: radial and bilateral symmetry; diploblastic and triploblastic; spiral and radial cleavage; determinate and indeterminate cleavage; acoelomate, pseudocoelomate, and coelomate
Compare the developmental differences between protostomes and deuterostomes.