Unit III: Intro to Metazoa

Question 1

What are the 4 Tree of Life branches of Metazoa (Animalia)?

Answer 1

1. Ctenophora
2. Porifera
3. Cnidaria
4. Bilateral

Question 2

What are Metazoa characteristics?

Answer 2

• All are multicellular heterotrophs
• All animals move under their own power at some point in their life cycle
• Variety of tissue types (except sponges, all have neurons & muscle cells that lack cell walls)

Question 3

How do the Metazoa reproduce?

Answer 3

• Most species have sexual reproduction (production of haploid gametes to fertilization)
• Some species area capable of asexual reproduction (budding an outgrowth of the body or unfertilized eggs)

Question 4

What are the steps of Metazoa development?

Answer 4

• Development begins with the cleavage
• Formation of (typically hollow) blastula
• Gastrulation

Question 5

Cleavage

Answer 5

cell divisions subdividing a fertilized egg (zygote) to form a multicellular embryo

Question 6

Blastula

Answer 6

16-32 cell stage of development of an animal

Question 7

Gastrulation

Answer 7

process in which the blastula folds over itself to form three germ layers

Question 8

Germ layers

Answer 8

collection of cells formed during embryogenesis that will give rise to future body tissues

Question 9

Diploblasts

Answer 9

animal that develops from two germ layers (most internal to external: endoderm, non-living layer, ectoderm)

Question 10

Triploblasts

Answer 10

animal that develops from three germ layers (most internal to external: endoderm, mesoderm, ectoderm)

Question 11

Blastomeres

Answer 11

The cells resulting from subdivision of the material of the egg where cells are not growing, only dividing

Question 12

What are the 2 groups of Triplobastic animals based on development?

Answer 12

• Protostomes = “mouth first”
• Deuterostomes = “mouth second”

Question 13

What is an example of some animals having larval forms that are different from adult?

Answer 13

Insect metamorphosis

Question 14

Incomplete metamorphosis

Answer 14

larval forms are smaller, wingless version of adult

Question 15

Complete metamorphosis

Answer 15

larval stage differs greatly in body plan compared to adults

Question 16

Hox genes

Answer 16

Master control gene that can turn on or off large numbers of other genes during embryogenesis
- Important factor in determining body plan

Question 17

Duplications across evolutionary time _______ correlate with body plan complexity.

Answer 17

positively

Question 18

Bilateral symmetry

Answer 18

type of symmetry in which there is only one plane of symmetry, so the left and right halves of an animal are mirror images

Question 19

Radial symmetry

Answer 19

division in any direction along oral/oboral axis results in two halves that are mirror images

Question 20

Rotational symmetry

Answer 20

division in any direction along oral/oboral axis results in two identical halves, with one copy rotated 180o

Question 21

Porifera-sister hypothesis

Answer 21

Systematic studies typically place Porifera (sponges) as sister to all other animals; first branch off the ToL

• “primitive” traits: lack germ layers, nerve and muscle cells
• cells that resemble choanoflagellates

Question 22

What is the truth of the Porifera-sister hypothesis?

Answer 22

Recent studies using DNA sequence data place Ctenophora (comb jellies) as sister to all other animals
- traditionally grouped closer to Cnidaria (includes jellyfish)
- lack Hox genes

Still debated, but if true then either:
- porifera lost complexity (e.g. nerve & muscle cells)
- complexity evolved twice

Question 23

What are key traits of Metazoa?

Answer 23

• muscle cells
• neurons
• diploblasty

Question 24

Cambrian explosion

Answer 24

time during the Cambrian period when most of the animal phyla in existence today evolved

• Rapid diversification of animals, including new body plans

Question 25

What are possible mechanisms of the Cambrian explosion?

Answer 25

• Increase in atmospheric oxygen
• Increase in oceanic calcium
• Changes in ecology and species interactions
• Expansion of Hox genes