Chapter 32 Introduction to Animal Evolution

I. Characteristics of Animals

A. What is the meaning of “Animals are multicellular, heterotrophic

eukaryotes.”?

B. Animals lack what that provide support to bodies of plants and fungi?

Cell walls

C. What hold animal cells to each other?

1. Collagen, a structural

2. Junctions: gap, tight, and desmosomes

D. What tissues unique to animals are responsible for impulse conduction and

movement?

1. Nervous

2. Muscle

E. Most animals reproduce sexually.

1. Which stage dominates the life cycle – diploid or haploid?

2. Compare a sperm with an egg.

3. What is a blastula?

multicellular stage of development. In most animals a hollow ball

4. What is gastrulation?

The next stage that leads to a gastrula, layers of embryonic tissue form

5. What is a larva?

Sexually immature stage that exists in some animals

6. What is metamorphosis?

Transformation of larva into adult – complete vs incomplete

II. Animal phylogeny and Diversity

A. The animal kingdom is monophyletic. What does this mean?

All animals have a common ancestor.

B. What are the four key evolutionary branch points in animal phylogeny? (Each

branch point represents a grade. All animals that belong to the same branch or

grade share certain body-plans.)

1. Contrast Parazoa with Eumetazoa: Multicellular animals without true

tissues, the parazoa (for ex. sponges) splitting from the animals with

true tissues, the eumetazoa (most animals).

2. Contrast Radiata with Bilateria: Eumetazoa (animals with true tissues)

with body symmetry developed

a. Radial symmetry – Cnidaria (hydras, “jellyfishes”, sea

anemones, corals) - Many planes through the central axis

would divide the animal into mirror images.

b. Bilateral symmetry – Only one plane would divide the animal

into mirror images

1) To what do the terms dorsal, ventral, anterior, posterior,

lateral refer?

2) What is cephalization, which is associated with bilateral

animals?

Development of a head with a concentration of sensory

equipment and usually a central nervous system

extending toward the tail as a longitudinal nerve cord

3) Animals who move actively from place to place tend to

be bilateral or radial?

c. Another difference in body plan developed with the radial

bilateral animal split – that is the layering of the embryo.

1) All animals have the two layers called what?

The ectoderm (which often develops into the CNS) and

endoderm (which becomes the lining of the digestive

tube, or archenterons and other organs derived from it

like the liver and lungs of vertebrates.

2) All bilateral animals also have a third layer called

what? (Radially symmetrical animals don’t have

mesoderm.)

The mesoderm, which forms the muscles and most

other organs between the digestive tube and the outer

covering of the animal

3) What are diploblastic and triploblastic?

Two layers and three layers

Radial animals are diploblastic,

bilateral are triploblastic

3. Contrast Acoelomate, Pseudocoelomate, Coelomate.

Why is the development of body cavities important, and what different

types exist?

a. Body cavity provides space for internal organs to grow and

move independently of the outer body wall

b. Its fluid cushions the suspended organs

c. Acoelomates are without a body cavity but have three layers

(flatworms – Platyhelminthes)

d. Pseudocoelom – body cavity is not completely lined by tissue

derived from mesoderm (roundworms - Nematoda, and

Rotifera)

e. Coelom – fluid filled body cavity completely lined by tissue

derived from mesoderm.

f. Differences in body cavities of lack of indicate evolutionary

relationships

4. Contrast the branches of the coelomates: protostomes and

deuterostomes. What are the differences?

a. They include two distinct evolutionary lines of coelomates.

b. Protostomes include Mollusks, Annelida Arthropoda

c. Deuterostomes include Echinodermata and Chordata

fig 32.6 d. Protostomes – blastopore becomes mouth

e. Deuterostomes – blastopore becomes anus

f. Many protostomes undergo spiral cleavage and determinate

cleavage.

g. Many deuterostomes undergo radial cleavage and

indeterminate cleavage

h. Coeloms form by different means

III. The brief development of most animal phyla occurred rapidly about 565 to 525

million years ago.

A. What was the Cambrian explosion?

A period of time during which the first animals with hard mineralized

skeletons existed, leaving fossils including the Burgess Shale in

British Columbia

B. Why do scientists have to depend on clues from comparative anatomy,

embryology, developmental genetics, and molecular systematics instead of

fossils when reconstructing evolutionary history of animals?

Because animals diversified so rapidly that sorting out the sequence of

animals is difficult.

C. What might have caused such rapid diversification of bilateral animals?

1. Predator-prey relationships, which triggered many evolutionary

adaptations, incl. shells, locomotion, protection

2. Atmospheric oxygen was increasing