Question 1

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 lack true tissues, whereas all other animal phyla have organized tissues. The absence or presence of a body cavity (A), complete digestive tract (B), and mesoderm (C) are not reliable distinctions between sponges and other animal phyla.

Question 2

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, as they diverged early in metazoan evolution and did not evolve the ability to form tissues.

Question 3

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 4

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 proposed evidence that supports sponges as the basal group includes fossil steroids, molecular clock, lack of tissues in sponges, and the structure of collar cells. Fossil steroids are molecules found in ancient rocks that suggest the presence of early animals. Molecular clock is a method that compares the genetic sequences of different organisms to estimate how long ago they shared a common ancestor. The lack of tissues in sponges is considered a primitive characteristic, and the structure of collar cells is unique to sponges, suggesting an ancient origin. Therefore, choice C is the best answer as it includes all of these pieces of evidence.

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 occurred much later than the Cambrian explosion and therefore could not have been a factor in bringing it about. The emergence of predator-prey relationships and the origin of Hox genes are both considered important factors in the Cambrian explosion, while an increase in atmospheric oxygen may have provided an environment conducive to the evolution of complex animal life.

Question 6

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 7

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 not more closely related to echinoderms than to annelids. This statement is false because acoelomate flatworms are actually more closely related to annelids than to echinoderms.

Quiz 32: An Overview of Animal Diversity

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

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

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?

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?

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

One of the characteristics unique to animals is

Based on the tree shown, which statement is false?