Topic 20: Origin of Animals

Question 1

Morphological and molecular data suggest that the

protist common ancestor of animals was a

Answer 1

flagellated eukaryote

Question 2

choanoflagellates

Answer 2

• small unicellular, heterotrophic protists
• Choanoflagellates are collared flagellates (choano = collar), with a funnel-shaped collar of microvilli at
  the base of a flagellum

Question 3

Evidence that choanoflagellates are closely related to animals

Answer 3

DNA sequence data indicate that choanoflagellates and animals are sister groups, Choanoflagellate cells and the collar cells of sponges are almost indistinguishable, Cells resembling choanoflagellates are found in other animals, but never in non-choanoflagellate protists, plants, or fungi.

Question 4

The earliest complex, multicellular animal fossils are

from the

Answer 4

Ediacaran biota

Question 5

Most animal fossils from the Cambrian explosion are

Answer 5

bilaterians with:
 Bilaterally symmetrical body plan.
 Complete digestive tract with one-way digestive system

Question 6

Several hypotheses for the cause of the Cambrian explosion

Answer 6

• New predator-prey relationships.
  − A rise in atmospheric/oceanic [O2] supported greater body size and more energetic lifestyles.
  − Evolution of the Hox gene complex

Question 7

Clade Metozoa

Answer 7

1. Multicellularity and cell differentiation
2. Cell adhesion (extracellular matrix)
3. Sperm and ova (egg)
4. Embryonic blastula

Question 8

Clade Eumetazoa

Answer 8

1. True tissues

2. Gastrulation

Question 9

Clade Bilateria

Answer 9

1. Bilateral symmetry
2. Triploblastic
3. Complex organs