Question 1

One of the characteristics unique to animals is
A) gastrulation.
B) multicellularity.
C) sexual reproduction.
D) flagellated sperm.

Accepted Answer

Gastrulation is a process unique to animals, involving the early developmental stage where the embryo reorganizes into a layered structure, a critical step in the development of the body plan of the animal. Multicellularity, sexual reproduction, and flagellated sperm are found in other life forms as well, not just animals.

Question 2

Based on the tree shown, which statement is false?
A) The animal kingdom is monophyletic.
B) Acoelomate flatworms are more closely related to echinoderms than to annelids.
C) Sponges are basal animals.
D) Bilaterians form a clade.

Accepted Answer

Acoelomate flatworms are more closely related to annelids than to echinoderms. Therefore, statement B is false. The other statements are true: A) The animal kingdom is monophyletic, meaning that all animals share a common ancestor. C) Sponges are basal animals, meaning that they are the most primitive group of animals. D) Bilaterians form a clade, which includes all animals with bilateral symmetry.

Question 3

Sponges and ctenophores have both been proposed as basal metazoans. Which of the following types of data support the idea that sponges are the basal group?
A) sequences of cadherin genes, cleavage type, structure of collar cells, and bilateral symmetry of adults
B) sequences of collagen genes, bilateral symmetry of adults, cleavage type, and fossil steroids
C) fossil steroids, molecular clock, lack of tissues in sponges, and structure of collar cells
D) structure of collar cells, bilateral symmetry of larvae, sequences of cadherin genes, and molecular clock

Accepted Answer

The fossil record shows that sponges have been present for at least 635 million years, making them the oldest known animal group. Molecular clock studies also suggest that sponges diverged from the rest of the metazoans earlier than ctenophores. Additionally, sponges lack true tissues, which is a primitive characteristic, while ctenophores have developed tissue-level organization. Fossil steroids have been found in ancient sponge fossils, providing further evidence for their basal position. Therefore, the data that support the idea that sponges are the basal group are: fossil steroids, molecular clock, lack of tissues in sponges, and the structure of collar cells is not necessary as choosing option C already suits the answer.

Question 4

Sponges and ctenophores have both been proposed as basal metazoans. Imagine that you wanted to provide additional evidence to help resolve this question. Which of the following projects would be the best next step?
A) more extensive study of DNA sequences in the bilateria
B) ultrastructural (that is, electron microscope) comparisons of choanoflagellates and sperm cells from arthropods
C) measurements of molecular clocks from the Lophotrochozoa
D) more extensive studies of DNA sequences in both groups

Accepted Answer

The answer of Sponges and ctenophores have both been proposed...

Question 5

Which of the following was probably the least important factor in bringing about the Cambrian explosion?
A) the emergence of predator-prey relationships
B) an increase in the concentration of atmospheric oxygen
C) the movement of animals onto land
D) the origin of Hox genes

Accepted Answer

The movement of animals onto land did not occur until much later in the history of life (during the colonization of land by plants and animals in the Devonian period), while the Cambrian explosion occurred in the oceans. The emergence of predator-prey relationships, an increase in atmospheric oxygen, and the origin of Hox genes have all been suggested as factors contributing to the rapid diversification of animal life during the Cambrian period.

Question 6

Placing sponges as the basal metazoans on the basis of lack of tissues implies which of the following?
A) Sponge ancestors never had tissues.
B) Modern-day sponges have lost the ability to form tissues.
C) Multicellular, modern-day choanoflagellates can form tissues.
D) Sponges do not have nerve cells.

Accepted Answer

Placing sponges as the basal metazoans on the basis of lack of tissues implies that sponge ancestors never had tissues. This is because they are the earliest branching animals and do not possess any tissues or organs, which suggests that their ancestors did not have them either.

Question 7

The distinction between sponges and other animal phyla is based mainly on the absence versus the presence of
A) a body cavity.
B) a complete digestive tract.
C) mesoderm.
D) tissues.

Accepted Answer

Sponges are the only animal phylum that lack true tissues, while all other animal phyla have some degree of specialization of cells into tissues.

Quiz 32: An Overview of Animal Diversity

One of the characteristics unique to animals is

Based on the tree shown, which statement is false?

Sponges and ctenophores have both been proposed as basal metazoans. Which of the following types of data support the idea that sponges are the basal group?

Sponges and ctenophores have both been proposed as basal metazoans. Imagine that you wanted to provide additional evidence to help resolve this question. Which of the following projects would be the best next step?

Which of the following was probably the least important factor in bringing about the Cambrian explosion?

Placing sponges as the basal metazoans on the basis of lack of tissues implies which of the following?

The distinction between sponges and other animal phyla is based mainly on the absence versus the presence of