Chapter 32: An Introduction to Animal Diversity,
Overview: Welcome to Your Kingdom
•The animal kingdom extends far beyond humans and other animals we
•1.3 million living species of animals have been identified
Concept 32.1 Animals are multicellular, heterotrophic eukaryotes with
tissues that develop from embryonic layers
1. Like the fungi, animals are multicellular heterotrophs. How do they
•Animals are heterotrophs that ingest their food
2. What two types of specialized cells do only animals have?
•Nervous tissue and muscle tissue are unique to animals
3. Most animals reproduce sexually, and the diploid stage dominates the
4. Animal development requires its own vocabulary to describe the
stages that are seen in all developing embryos. To help learn
them, label each stage shown in this figure.
5. Your sketch labels should include the following terms. Define each
Zygote: (zī′-gōt) The diploid product of the union of haploid gametes
during fertilization; a fertilized egg.
•Most animals reproduce sexually, with the diploid stage usually
dominating the life cycle
Blastula: (blas′-tyū-luh) A hollow ball of cells that marks the end of the
cleavage stage during early embryonic development in animals.
•Cleavage leads to formation of a blastula
Gastrula: (gas′-trū-luh) An embryonic stage in animal development
encompassing the formation of three layers: ectoderm, mesoderm,
Blastopore: (blas′-tō-pōr) In a gastrula, the opening of the archenteron
that typically develops into the anus in deuterostomes and the
mouth in protostomes.
6. Explain these terms:
Cleavage: (1) The process of cytokinesis in animal cells, characterized
by pinching of rapid cell divisions without significant growth during
early embryonic development that converts the zygote to a ball of
•After a sperm fertilizes an egg, the zygote undergoes rapid cell
division called cleavage
Gastrulation: (gas′-trū-lā′-shun) In animal development, a series of cell
and tissue movements in which the blastula-stage embryo folds
inward, producing a three-layered embryo, the gastrula.
•The blastula undergoes gastrulation, forming a gastrula with different
layers of embryonic tissues
Metamorphosis: (met′-uh-mōr′-fuh-sis) A developmental transformation
that turns an animal larva into either an adult or an adult-like
stage that is not yet sexually mature.
•A larva is sexually immature and morphologically distinct from the
adult; it eventually undergoes metamorphosis
7. All eukaryotes have sets of regulatory genes containing common sets
of DNA sequences called homeoboxes. What are the unique
homeobox genes of animals called?
(hō′-mē-ō-boks′) A 180-nucleotide sequence within homeotic genes and
some other developmental genes that is widely conserved in
animals. Related sequences occur in plants and yeasts.
•All animals, and only animals, have Hox genes that regulate the
development of body form
•Although the Hox family of genes has been highly conserved, it can
produce a wide diversity of animal morphology
Concept 32.3 Animals can be characterized by “body plans”
8. Which animal group lacks symmetry? Sponges
•Animals can be categorized according to the symmetry of their bodies,
or lack of it
9. Two types of symmetry are seen in all other animal groups. Name and
describe them in words or with a sketch.
•Some animals have radial symmetry
•Two-sided symmetry is called bilateral symmetry
Bilaterally symmetrical animals have:
–A dorsal (top) side and a ventral (bottom) side
–A right and left side
–Anterior (head) and posterior (tail) ends
–Cephalization, the development of a head
10. What is the symmetry of a jellyfish? Radial - of a worm? Bilateral
- of a dog? Bilateral
11. Animals that have bilateral symmetry have a front and rear. Draw a
sketch of a cat, and label these regions:
1. Anterior: Pertaining to the front, or head, of a bilaterally
2. Posterior: Pertaining to the rear, or tail end, of a bilaterally
3. Dorsal: Pertaining to the top of an animal with radial or bilateral
4. Ventral: Pertaining to the underside, or bottom, of an animal with
12. Does your cat have whiskers, eyes, and ears? With bilateral
symmetry, major sensory structures and the “brain” are
concentrated in the head region. What is this area called?
Cephalization: (sef′-uh-luh-zā′-shun) An evolutionary trend toward the
concentration of sensory equipment at the anterior end of the
13. Many animals with radial symmetry are sessile. What does this
mean? Living attached to a substrate
14. How is radial symmetry an advantage to sessile or planktonic
Their symmetry equips them to navigate the environment equally well
from all sides.
15. The process of gastrulation results in concentric layers in the
embryo and the development of a body tube called the
archenteron, which becomes the gut. Return to the figure in
question 4, and label the archenteron and the three tissue layers:
endoderm, ectoderm, and mesoderm. If this diagram is not
printed in color, use pencils to color the ectoderm blue, the
mesoderm red, and the endoderm yellow. These colors are used by
convention for each tissue type.
16. Which animal groups have only two tissue layers and are said to be
Cnidarians (jellies and corals) and comb jellies
•Diploblastic animals have ectoderm and endoderm
17. For a triploblastic animal, give at least two organs or organ systems
that arise from each tissue layer (also called germ layer).
The mesoderm forms the muscles and the outer covering of most other
organs between the digestive tract and the outer covering of the
(Wide range of animal from flatworms to arthropods)
•Triploblastic animals that lack a body cavity are called acoelomates
Germ Layer Organ or Organ System
Endoderm is the innermost germ layer and lines the developing digestive
tube, called the archenteron
Mesoderm (mez′-ō-derm) The middle primary germ layer in an animal
embryo; develops into the notochord, the lining of the coelom, muscles,
skeleton, gonads, kidneys, and most of the circulatory system in species
that have these structures.
Musculature, Skeletal, Male reproductive (gonads), Urinary (bladder),
and most of the Circulatory system
•Ectoderm is the germ layer covering the embryo’s surface
•Most triploblastic animals possess a body cavity
•A true body cavity is called a coelom and is derived from mesoderm
18. (Now we are going to move into a discussion that many students find
confusing. Pay close
attention!) What is a coelom?
Coelom: (sē′-lōm) (1) A body cavity is surrounded [lined] by mesoderm on
both sides. (2) A body cavity lined by tissue derived only from
•Coelomates are animals that possess a true coelom
•In protostome development, the splitting of solid masses of mesoderm
forms the coelom
•In deuterostome development, the mesoderm buds from the wall of the
archenteron to form the coelom
19. The definition you have written should say the body cavity is
surrounded by mesoderm on both sides. What do we call the animal
groups that have a body cavity with mesoderm on only one side?
•A pseudocoelom is a body cavity derived from the mesoderm and
•Triploblastic animals that possess a pseudocoelom are called
pseudocoelomate: (sū′-dō-sē′-lō-māt) An animal whose body cavity is
lined by tissue derived from mesoderm and endoderm.
20. What are the animal groups called that have no body cavity?
•Triploblastic animals that lack a body cavity are called acoelomates
21. Here’s what students find confusing: the gut or digestive tube is not
a coelom? All the animals sketched below have a digestive tube, but only
one has a true coelom. Using the colors described in question 15, color
the germ layers, and label these representative animals coelomate –
earthworms, pseudocoelomate – roundworms, acoelomate –planaria.
Indicate the body cavity and gut in the pictures. Also, give the common
names of the animals shown.
1. Coelomate – earthworms;
2. Pseudocoelomate – roundworms; and
3. Acoelomate –planaria.
22. What are three functions of the body cavity?
1. It’s fluid cushions the suspended organs, helping to prevent
2. In soft bodied coelomates, such as earthworms, the coelom
contains noncompressible fluid that acts like a skeleton against
which muscles can work; and
3. The cavity also allows organs to grow and move independently of
the outer body wall. If it were not for your coelom, every beat of
your heart or ripple of your intestine would warp your body’s
Protosome and Deuterostome Development
This concept is one that students often find difficult, but it is
important to help you understand the major features that are used to
organize the animal groups. Stick with it until you understand and know
what is meant by protosome or deuterostome. Let’s begin with explaining
the meaning of these words based on their roots.
With a protostome, the blastopore (which is the opening into the
aechenteron) becomes the mouth (first mouth), and a second opening in
the body tube will form the anus.
With a deuterostome, the blastopore will be the anus, and a second
opening becomes the mouth (second mouth).
23. Label protostome, deuterostome, mouth, anus, and digestive tube on
the figure above.
24. What forms the mouth in a deuterostome?
•In protostome development, the blastopore becomes the mouth
•In deuterostome development, the blastopore becomes the anus; and
the mouth forms from a seconday opening.
25. Now let’s layer on another set of words based on the early mitotic
divisions of the embryo called cleavages. Study the figure below. If the
cells are lined up over each other in the eight cell embryo, the cleavages
are said to be radial. If the top layer is rotated relative to the lower
layer, the cleavages are said to be spiral. Label the cleavages below in
•Based on early development, many animals can be categorized as having
protostome development or deuterostome development
26. If each cell in the early embryo has the capacity to develop into a
complete embryo, what is this type of cleavage called?
Indeterminate cleavage: A type of embryonic development in
deuterostomes in which each cell produced by early cleavage divisions
retains the capacity to develop into a complete embryo.
27. What type of cleavage is it if the developmental fate of each
embryonic cell is rigidly “determined” very early?
Determinate cleavage: A type of embryonic development in protostomes
that rigidly casts the developmental fate of each embryonic cell very
28. You will notice that most animal’s have
spiral and determinate cleavage or radial and indeterminate cleavage.
•In protostome development, cleavage is spiral and determinate
•In deuterostome development, cleavage is radial and indeterminate
29. Label the figure below with protostome and
deuterostome, spiral and determinate cleavage, and radial and
30. Many times you have heard that taxonomy is in a flux. Your text
shows two different phylogenetic trees based on analysis of different
criteria. Use the phylogenetic trees to answer these questions.
Animals in which phylum or phyla …
•All animals share a common ancestor
•Eumetazoa is a clade of animals (eumetazoans) with true tissues
•Most animal phyla belong to the clade Bilateria, and are called
1. Lack symmetry and true tissues: Sponges (basal animals), Calcarea
or phylum Silicea
2. Show radial symmetry and are diploblastic:
3. Have three tissue layers, but lack a body cavity: Show bilateral
symmetry and have a pseudocoelom: •Acoela (basal bilaterians)
•Triploblastic animals that lack a body cavity are called
4. Have a true coelom and are protostomes: Protostomia
5. Have a true coelom and are deuterostomes:
6. Are your closest relatives:
If you can group the animal phyla based on the characteristics above,
you are ready for the most common type of animal questions you will see
on the AP Biology exam!
Now you should be ready to Test Your Knowledge.
Place your answers here. Testing Your knowledge Self-Quiz answers:
1. ________ 2. ________ 3. (You may omit three.) ________ 4.