32

Chapter 32 An Introduction to Animal Diversity
Multiple-Choice Questions
1) Which of the following terms or structures is properly associated only with animals?
A) Hox genes
B) cell wall
C) autotrophy
D) sexual reproduction
E) chitin

A

Concept 32.1
Skill: Knowledge/Comprehension
2) Both animals and fungi are heterotrophic. What distinguishes animal heterotrophy from fungal heterotrophy is
that only animals derive their nutrition
A) from organic matter.
B) by preying on animals.
C) by ingesting it.
D) by consuming living, rather than dead, prey.
E) by using enzymes to digest their food.

C

Concept 32.1
Skill: Knowledge/Comprehension
3) The larvae of some insects are merely small versions of the adult, whereas the larvae of other insects look
completely different from adults, eat different foods, and may live in different habitats. Which of the following
most directly favors the evolution of the latter, more radical, kind of metamorphosis?
A) natural selection of sexually immature forms of insects
B) changes in the homeobox genes governing early development
C) the evolution of meiosis
D) B and C only
E) A, B, and C

B

Concept 32.1
Skill: Application/Analysis
4) Which of the following is (are) unique to animals?
A) cells that have mitochondria
B) the structural carbohydrate, chitin
C) nervous conduction and muscular movement
D) heterotrophy
E) both A and C

C

Concept 32.1
Skill: Knowledge/Comprehension
Page 1
5) The number of legs an insect has, the number of vertebrae in a vertebral column, or the number of joints in a
digit (such as a finger) are all strongly influenced by
A) haploid genomes.
B) introns within genes.
C) heterotic genes.
D) heterogeneous genes.
E) Hox genes.

E

Concept 32.1
Skill: Application/Analysis
6) What do animals as diverse as corals and monkeys have in common?
A) body cavity between body wall and digestive system
B) number of embryonic tissue layers
C) type of body symmetry
D) presence of Hox genes
E) degree of cephalization

D

Concept 32.1
Skill: Knowledge/Comprehension
7) The Hox genes came to regulate each of the following in what sequence, from earliest to most recent?
1. identity and position of paired appendages in protostome embryos
2. formation of water channels in sponges
3. anterior-posterior orientation of segments in protostome embryos
4. positioning of tentacles in cnidarians
5. anterior-posterior orientation in vertebrate embryos
A) 4 → 1 → 3 → 2 → 5
B) 4 → 2 → 3 → 1 → 5
C) 4 → 2 → 5 → 3 → 1
D) 2 → 4 → 5 → 3 → 1
E) 2 → 4 → 3 → 1 → 5

E

Concept 32.1
Skill: Synthesis/Evaluation
8) In individual insects of some species, whole chromosomes that carry larval genes are eliminated from the
genomes of somatic cells at the time of metamorphosis. A consequence of this occurrence is that
A) we could not clone a larva from the somatic cells of such an adult insect.
B) such species must reproduce only asexually.
C) the descendents of these adults do not include a larval stage.
D) metamorphosis can no longer occur among the descendents of such adults.
E) both C and D.

A

Concept 32.1
Skill: Application/Analysis
Page 2
9) The last common ancestor of all animals was probably a
A) unicellular chytrid.
B) unicellular yeast.
C) plant.
D) multicellular fungus.
E) flagellated protist.

E

Concept 32.2
Skill: Knowledge/Comprehension
10) Almost all of the major animal body plans seen today appeared in the fossil record over 500 million years ago
at the beginning of the
A) Cambrian period.
B) Ediacaran period.
C) Permian period.
D) Carboniferous period.
E) Cretaceous period.

A

Concept 32.2
Skill: Knowledge/Comprehension
11) Evidence of which structure or characteristic would be most surprising to find among fossils of the Ediacaran
fauna?
A) true tissues
B) hard parts
C) bilateral symmetry
D) cephalization
E) embryos

B

Concept 32.2
Skill: Knowledge/Comprehension
12) Which statement is most consistent with the hypothesis that the Cambrian explosion was caused by the rise of
predator-prey relationships?
A) increased incidence of worm burrows in the fossil record
B) increased incidence of larger animals in the fossil record
C) increased incidence of organic material in the fossil record
D) increased incidence of fern galls in the fossil record
E) increased incidence of hard parts in the fossil record

E

Concept 32.2
Skill: Application/Analysis
13) Which of these genetic processes may be most helpful in accounting for the Cambrian explosion?
A) binary fission
B) mitosis
C) random segregation
D) gene duplication
E) chromosomal condensation

D

Concept 32.2
Skill: Knowledge/Comprehension
Page 3
14) Whatever its ultimate cause(s), the Cambrian explosion is a prime example of
A) mass extinction.
B) evolutionary stasis.
C) adaptive radiation.
D) A and B only
E) A, B, and C

C

Concept 32.2
Skill: Knowledge/Comprehension
15) Fossil evidence indicates that the following events occurred in what sequence, from earliest to most recent?
1. Protostomes invade terrestrial environments.
2. Cambrian explosion occurs.
3. Deuterostomes invade terrestrial environments.
4. Vertebrates become top predators in the seas.
A) 2 → 4 → 3 → 1
B) 2 → 1 → 4 → 3
C) 2 → 4 → 1 → 3
D) 2 → 3 → 1 → 4
E) 2 → 1 → 3 → 4

C

Concept 32.2
Skill: Knowledge/Comprehension
16) What is the probable sequence in which the following clades of animals originated, from earliest to most
recent?
1. tetrapods
2. vertebrates
3. deuterostomes
4. amniotes
5. bilaterians
A) 5 → 3 → 2 → 4 → 1
B) 5 → 3 → 2 → 1 → 4
C) 5 → 3 → 4 → 2 → 1
D) 3 → 5 → 4 → 2 → 1
E) 3 → 5 → 2 → 1 → 4

B

Concept 32.2
Skill: Knowledge/Comprehension
17) Sponges and cnidarians are among the fossilized animals found in both the Ediacara Hills and the Burgess
Shale from the Rocky Mountains of British Colombia. This observation requires that
A) ancestral sponges and cnidarians had formerly been terrestrial animals.
B) North America and Australia were united to each other about 550 million years ago (mya).
C) land that now comprises the Ediacara Hills and the Rocky Mountains was underwater about 550 million
years ago.
D) only sponges and cnidarians existed at the time the sediments were deposited.

C

Concept 32.2
Skill: Application/Analysis
Page 4
18) Arthropods invaded land about 100 million years before vertebrates did so. This most clearly implies that
A) arthropods evolved before vertebrates did.
B) extant terrestrial arthropods are better adapted to terrestrial life than are extant terrestrial vertebrates.
C) ancestral arthropods must have been poorly adapted to aquatic life, thus experienced a selective pressure
to invade land.
D) vertebrates evolved from arthropods.
E) arthropods have had more time to co-evolve with land plants than have vertebrates.

E

Concept 32.2
Skill: Application/Analysis
19) An adult animal that possesses bilateral symmetry is most certainly also
A) triploblastic.
B) a deuterostome.
C) eucoelomate.
D) the product of metamorphosis.
E) highly cephalized.

A

Concept 32.2
Skill: Knowledge/Comprehension
20) An obsolete taxon, the ʺRadiata,ʺ included all phyla whose adults had true radial symmetry. Today, the
ʺRadiataʺ is more correctly considered to be
1. a clade.
2. a grade.
3. monophyletic.
4. paraphyletic.
5. polyphyletic.
A) 1 and 2
B) 1 and 3
C) 2 and 4
D) 2 and 5
E) 1, 2, and 3

C

Concept 32.3
Skill: Application/Analysis
21) Soon after the coelom begins to form, a researcher injects a dye into the coelom of a deuterostome embryo.
Initially, the dye should be able to flow directly into the
A) blastopore.
B) blastocoel.
C) archenteron.
D) pseudocoelom.

C

Concept 32.3
Skill: Application/Analysis
Page 5
22) A researcher is trying to construct a molecular-based phylogeny of the entire animal kingdom. Assuming that
none of the following genes is absolutely conserved, which of the following would be the best choice on which
to base the phylogeny?
A) genes involved in chitin synthesis
B) collagen genes
C) beta-catenin genes
D) genes involved in eye-lens synthesis
E) genes that cause radial body symmetry

B

Concepts 32.1, 32.3
Skill: Application/Analysis
23) What is the correct sequence of the following four events during an animalʹs development?
1. gastrulation
2. metamorphosis
3. fertilization
4. cleavage
A) 4 → 3 → 2 → 1
B) 4 → 3 → 1 → 2
C) 3 → 2 → 4 → 1
D) 3 → 4 → 2 → 1
E) 3 → 4 → 1 → 2

E

Concept 32.3
Skill: Knowledge/Comprehension
24) At which developmental stage should one be able to first distinguish a diploblastic embryo from a triploblastic
embryo?
A) fertilization
B) cleavage
C) gastrulation
D) coelom formation
E) metamorphosis

C

Concept 32.3
Skill: Knowledge/Comprehension
25) At which developmental stage should one be able to first distinguish a protostome embryo from a
deuterostome embryo?
A) fertilization
B) cleavage
C) gastrulation
D) coelom formation
E) metamorphosis

B

Concept 32.3
Skill: Knowledge/Comprehension
Page 6
26) What may have occurred to prevent species that are of the same grade from also belonging to the same clade?
A) similar structures arising independently in different lineages
B) convergent evolution among different lineages
C) adaptation by different lineages to the same selective pressures
D) A and B only
E) A, B, and C

E

Concept 32.3
Skill: Knowledge/Comprehension
27) Organisms showing radial symmetry would likely
A) be good swimmers.
B) have rapid escape behavior.
C) move from place to place relatively slowly, if at all.
D) be able to fly.
E) have many fins.

C

Concept 32.3
Skill: Knowledge/Comprehension
28) During metamorphosis, echinoderms undergo a transformation from motile larvae to a sedentary (or
sometimes sessile) existence as adults. What differentiates echinoderm adults, but not their larvae? Adults
should
A) be diploblastic.
B) have radial symmetry, or something close to it.
C) lack mesodermally derived tissues.
D) A and B only
E) A, B, and C

B

Concept 32.3
Skill: Knowledge/Comprehension
29) Cephalization is primarily associated with
A) adaptation to dark environments.
B) method of reproduction.
C) fate of the blastopore.
D) type of digestive system.
E) bilateral symmetry.

E

Concept 32.3
Skill: Knowledge/Comprehension
30) Cephalization is most closely associated with which of the following?
A) sedentary lifestyle
B) concentration of sensory structures at the anterior end
C) predators, but not prey
D) a backbone
E) a sessile existence

B

Concept 32.3
Skill: Knowledge/Comprehension
Page 7
31) Which of the following is a correct association of an animal germ layer with the tissues or organs to which it
gives rise?
A) ectoderm: outer covering of digestive system
B) endoderm: internal lining of blood vessels
C) mesoderm: central nervous system
D) mesoderm: skin
E) endoderm: linings of liver passageways and lung passageways

C

Concept 32.3
Skill: Knowledge/Comprehension
32) You are trying to identify an organism. It is an animal, but it does not have nerve or muscle tissue. It is neither
diploblastic nor triploblastic. It is probably a
A) flatworm.
B) jelly.
C) comb jelly.
D) sponge.
E) nematode.

D

Concept 32.3
Skill: Application/Analysis
Page 8
Figure 32.1
Figure 32.1 shows a chart of the animal kingdom set up as a modified phylogenetic tree. Use the diagram to answer the following
questions.
33) Which group contains diploblastic organisms?
A) I
B) II
C) III
D) IV
E) V

A

Concepts 32.2-32.4
Skill: Knowledge/Comprehension
34) Which group consists of deuterostomes?
A) I
B) II
C) III
D) IV
E) V

B

Concepts 32.2-32.4
Skill: Knowledge/Comprehension
35) Which group includes both ecdysozoans and lophotrochozoans?
A) I
B) II
C) III
D) IV
E) V

C

Concepts 32.2-32.4
Skill: Knowledge/Comprehension
Page 9
36) Which two groups are most clearly represented in the Ediacaran fauna?
A) I and II
B) I and III
C) II and IV
D) II and V
E) IV and V

B

Concepts 32.2-32.4
Skill: Knowledge/Comprehension
37) Which of these is the basal group of the Eumetazoa?
A) I
B) II
C) III
D) IV
E) V

A

Concepts 32.2-32.4
Skill: Knowledge/Comprehension
38) Which two groups have members that undergo ecdysis?
A) I and II
B) II and III
C) III and IV
D) III and V
E) IV and V

C

Concepts 32.2-32.4
Skill: Knowledge/Comprehension
39) Organisms that are neither coelomate nor pseudocoelomate should, apart from their digestive systems, have
bodies that
A) are solid with tissue.
B) lack the ability to metabolize food.
C) are incapable of muscular contraction.
D) lack true tissues.
E) lack mesodermally derived tissues.

A

Concept 32.3
Skill: Knowledge/Comprehension
40) What distinguishes a coelomate animal from a pseudocoelomate animal is that coelomates
A) have a body cavity, whereas pseudocoelomates have a solid body.
B) contain tissues derived from mesoderm, whereas pseudocoelomates have no such tissue.
C) have a body cavity completely lined by mesodermal tissue, whereas pseudocoelomates do not.
D) have a complete digestive system with mouth and anus, whereas pseudocoelomates have a digestive tract
with only one opening.
E) have a gut that lacks suspension within the body cavity, whereas pseudocoelomates have mesenteries
that hold the digestive system in place.

C

Concept 32.3
Skill: Knowledge/Comprehension
Page 10
41) Which of the following functions is an advantage of a fluid-filled body cavity?
A) Internal organs are cushioned and protected from injury.
B) Organs can grow and move independently of the outer body wall.
C) The fluid within the cavity acts as a hydrostatic skeleton.
D) A and C only
E) A, B, and C

E

Concept 32.3
Skill: Knowledge/Comprehension
42) You have before you a living organism, which you examine carefully. Which of the following should convince
you that the organism is acoelomate?
A) It responds to food by moving toward it.
B) It is triploblastic.
C) It has bilateral symmetry.
D) It possesses sensory structures at its anterior end.
E) Muscular activity of its digestive system distorts the body wall.

E

Concept 32.3
Skill: Application/Analysis
43) An animal that swims rapidly in search of prey that it captures using visual senses concentrated at its anterior
end is likely to be
A) bilaterally symmetrical and cephalized.
B) coelomate and a protostome.
C) eumetazoan and asymmetrical.
D) diploblastic and radially symmetrical.
E) heterotrophic and sessile.

A

Concept 32.3
Skill: Knowledge/Comprehension
44) The blastopore is a structure that first becomes evident during
A) fertilization.
B) gastrulation.
C) the eight-cell stage of the embryo.
D) coelom formation.
E) cleavage.

B

Concept 32.3
Skill: Knowledge/Comprehension
45) The blastopore denotes the presence of an endoderm-lined cavity in the developing embryo, a cavity that is
known as the
A) archenteron.
B) blastula.
C) coelom.
D) germ layer.
E) blastocoel.

A

Concept 32.3
Skill: Knowledge/Comprehension
Page 11
46) Which of the following is descriptive of protostomes?
A) spiral and indeterminate cleavage, blastopore becomes mouth
B) spiral and determinate cleavage, blastopore becomes mouth
C) spiral and determinate cleavage, blastopore becomes anus
D) radial and determinate cleavage, blastopore becomes anus
E) radial and determinate cleavage, blastopore becomes mouth

B

Concept 32.3
Skill: Knowledge/Comprehension
47) Which of the following characteristics generally applies to protostome development?
A) radial cleavage
B) determinate cleavage
C) diploblastic embryo
D) blastopore becomes the anus
E) archenteron absent

B

Concept 32.3
Skill: Knowledge/Comprehension
48) Protostome characteristics generally include which of the following?
A) a mouth that develops secondarily, and far away from the blastopore
B) radial body symmetry
C) radial cleavage
D) determinate cleavage
E) absence of a body cavity

D

Concept 32.3
Skill: Knowledge/Comprehension
The following questions are based on the description below.
A student encounters an animal embryo at the eight-cell stage. The four smaller cells that comprise one hemisphere of the
embryo seem to be rotated 45 degrees and lie in the grooves between larger, underlying cells (spiral cleavage).
49) This embryo may potentially develop into a(n)
A) turtle.
B) earthworm.
C) sea star.
D) fish.
E) sea urchin.

B

Concept 32.3
Skill: Knowledge/Comprehension
50) If we were to separate these eight cells and attempt to culture them individually, then what is most likely to
happen?
A) All eight cells will die immediately.
B) Each cell may continue development, but only into an inviable embryo that lacks many parts.
C) Each cell may develop into a full-sized, normal embryo.
D) Each cell may develop into a smaller-than-average, but otherwise normal, embryo.

B

Concept 32.3
Skill: Knowledge/Comprehension
Page 12
51) If an undisturbed embryo is allowed to develop further, then one should expect that
A) the first opening of the gastrula will ultimately serve as the mouth.
B) upon metamorphosis, the resulting trochophore larva will gain a backbone.
C) upon gastrulation, a solid ball of cells will be produced.
D) both A and B
E) both B and C

A

Concept 32.3
Skill: Knowledge/Comprehension
52) The most ancient branch point in animal phylogeny is that between having
A) radial or bilateral symmetry.
B) a well-defined head or no head.
C) diploblastic or triploblastic embryos.
D) true tissues or no tissues.
E) a body cavity or no body cavity.

D

Concept 32.3
Skill: Knowledge/Comprehension
53) With the current molecular-based phylogeny in mind, rank the following from most inclusive to least
inclusive.
1. ecdysozoan
2. protostome
3. eumetazoan
4. triploblastic
A) 4, 2, 3, 1
B) 4, 3, 1, 2
C) 3, 4, 1, 2
D) 3, 4, 2, 1
E) 4, 3, 2, 1

D

Concept 32.4
Skill: Knowledge/Comprehension
54) What does recent evidence from molecular systematics reveal about the relationship between grades and
clades?
A) They are one and the same.
B) There is no relationship.
C) Some, but not all, grades reflect evolutionary relatedness.
D) Grades have their basis in, and flow from, clades.
E) Each branch point on a phylogenetic tree is associated with the evolution of a new grade.

C

Concept 32.4
Skill: Knowledge/Comprehension
Page 13
55) What is characteristic of all ecdysozoans?
A) the deuterostome condition
B) some kind of exoskeleton, or hard outer covering
C) a pseudocoelom
D) agile, speedy, and powerful locomotion
E) the diploblastic condition

B

Concept 32.4
Skill: Knowledge/Comprehension
56) What kind of data should probably have the greatest impact on animal taxonomy in the coming decades?
A) fossil evidence
B) comparative morphology of living species
C) nucleotide sequences of homologous genes
D) similarities in metabolic pathways
E) the number and size of chromosomes within nuclei

C

Concept 32.4
Skill: Knowledge/Comprehension
57) Phylogenetic trees are best described as
A) true and inerrant statements about evolutionary relationships.
B) hypothetical portrayals of evolutionary relationships.
C) the most accurate representations possible of genetic relationships among taxa.
D) theories of evolution.
E) the closest things to absolute certainty that modern systematics can produce.

B

Concept 32.4
Skill: Knowledge/Comprehension
58) According to the evidence collected so far, the animal kingdom is
A) monophyletic.
B) paraphyletic.
C) polyphyletic.
D) euphyletic.
E) multiphyletic.

A

Concept 32.4
Skill: Knowledge/Comprehension
59) If a multicellular animal lacks true tissues, then it can properly be included among the
A) eumetazoans.
B) metazoans.
C) choanoflagellates.
D) lophotrochozoans.
E) bilateria.

B

Concept 32.4
Skill: Knowledge/Comprehension
Page 14
60) Which of the following organisms are deuterostomes?
A) molluscs
B) annelids
C) echinoderms
D) chordates
E) both C and D

E

Concept 32.4
Skill: Knowledge/Comprehension
61) Which of the following statements concerning animal taxonomy is (are) true?
1. Animals are more closely related to plants than to fungi.
2. All animal clades based on body plan have been found to be incorrect.
3. Kingdom Animalia is monophyletic.
4. Only animals reproduce by sexual means.
5. Animals are thought to have evolved from flagellated protists similar to modern choanoflagellates.
A) 5
B) 1, 3
C) 2, 4
D) 3, 5
E) 3, 4, 5

D

Concept 32.4
Skill: Knowledge/Comprehension
62) If the current molecular evidence regarding animal origins is well substantiated in the future, then what will be
true of any contrary evidence regarding the origin of animals derived from the fossil record?
A) The contrary fossil evidence will be seen as a hoax.
B) The fossil evidence will be understood to have been incorrect because it is incomplete.
C) The fossil record will henceforth be ignored.
D) Phylogenies involving even the smallest bit of fossil evidence will need to be discarded.
E) Only phylogenies based solely on fossil evidence will need to be discarded.

B

Concept 32.4
Skill: Synthesis/Evaluation
Page 15
The following eight questions refer to Figure 32.2A (morphological) and Figure 32.2B (molecular) phylogenetic trees of the animal
kingdom.
Figure 32.2A: Morphological Phylogeny
Page 16
Figure 32.2B: Molecular Phylogeny
63) According to both phylogenies depicted in Fig. 32.2, if one were to create a taxon called ʺRadiataʺ that included
all animal species whose members have true radial symmetry, then such a taxon would be
A) paraphyletic.
B) polyphyletic.
C) monophyletic.
D) a clade.
E) both C and D

A

Concept 32.4
Skill: Application/Analysis
Page 17
64) In the traditional phylogeny (Fig. 32.2A), the sponges are considered to be a clade, whereas in the molecular
phylogeny (Fig. 32.2B), sponges
A) do not all have a common ancestor that is unique only to them.
B) are polyphyletic.
C) called the Calcarea should actually be included among the eumetazoa.
D) called the Silicea are the sole organisms that should be properly called ʺsponges.ʺ
E) called the Calcarea diverged from the lineage that eventually produced the eumetazoa earlier than did
the Silicea.

A

Concept 32.4
Skill: Application/Analysis
65) If the traditional phylogeny (Fig. 32.2A) eventually becomes obsolete, the formerly close relationship depicted
between the annelids and arthropods will probably be viewed, in retrospect, as an instance of
A) scientific fraud.
B) lack of objectivity on the parts of arrogant or egotistical scientists.
C) scientists having mistakenly identified analogous features as homologous features.
D) the inherent invalidity of all evolutionary biology.
E) an evolutionary relationship that modern scientists had ʺset in stone,ʺ now having crumbled.

C

Concept 32.4
Skill: Synthesis/Evaluation
66) What is true of the deuterostomes in the molecular phylogeny (Fig. 32.2B) that is NOT true in the traditional
phylogeny (Fig. 32.2A)?
A) ʺDeuterostomiaʺ is a clade.
B) to maintain Deuterostoia as a clade, some phyla had to be removed from it.
C) Deuterostomia now includes the Acoela.
D) It is actually a grade, rather than a clade.
E) It diverged from the rest of the Bilateria earlier than did the Acoela.

B

Concept 32.4
Skill: Application/Analysis
67) In the traditional phylogeny (Fig. 32.2A), the phylum Platyhelminthes is depicted as a sister taxon to the rest of
the protostome phyla, and as having diverged earlier from the lineage that led to the rest of the protostomes. In
the molecular phylogeny (Fig. 32.2B), Platyhelminthes is depicted as a lophotrochozoan phylum. What
probably led to this change?
A) Platyhelminthes ceased to be recognized as true protostomes.
B) The removal of the acoel flatworms (Acoela) from the Platyhelminthes allowed the remaining flatworms
to be clearly tied to the lophotrochozoa.
C) All Platyhelminthes must have a well-developed lophophore as their feeding apparatus.
D) Platyhelminthesʹ close genetic ties to the arthropods became clear as their Hox gene sequences were
studied.

B

Concept 32.4
Skill: Synthesis/Evaluation
Page 18
68) What is true of the clade Ecdysozoa?
A) It includes all animals that molt at some time during their lives.
B) It includes all animals that undergo metamorphosis at some time during their lives.
C) It includes all animals that have body cavities known as pseudocoeloms.
D) It includes all animals with genetic similarities that are shared with no other animals.
E) It includes all animals in the former clade ʺProtostomiaʺ that truly do have protostome development.

D

Concept 32.4
Skill: Application/Analysis
69) Phylogenetic trees, such as those in Fig. 32.2, are best understood as being scientific
A) theories.
B) laws.
C) principles.
D) hypotheses.
E) dogmas.

D

Concept 32.4
Skill: Knowledge/Comprehension
70) Which distinction is given more emphasis by the morphological phylogeny than by the molecular phylogeny?
A) metazoan and eumetazoan
B) radial and bilateral
C) true coelom and pseudocoelom
D) protostome and deuterostome
E) molting and lack of molting

D

Concept 32.4
Skill: Knowledge/Comprehension
71) The last common ancestor of all bilaterians is thought to have had four Hox genes. Most extant cnidarians have
two Hox genes, except Nematostella (of beta-catenin fame), which has three Hox genes. On the basis of these
observations, some have proposed that the ancestral cnidarians were originally bilateral and, in stages, lost Hox
genes from their genomes. If true, this would mean that
A) ʺRadiataʺ should be a true clade.
B) The radial symmetry of extant cnidarians is secondarily derived, rather than being an ancestral trait.
C) Hox genes play little actual role in coding for an animalʹs ʺbody plan.ʺ
D) Cnidaria may someday replace Acoela as the basal bilaterians.
E) both B and D

E

Concept 32.4
Skill: Synthesis/Evaluation
Page 19
72) Which of these, if true, would support the claim that the ancestral cnidarians had bilateral symmetry?
1. Cnidarian larvae possess anterior-posterior, left-right, and dorsal-ventral aspects.
2. Cnidarians have fewer Hox genes than bilaterians.
3. All extant cnidarians, including Nematostella, are diploblastic.
4. Beta-catenin turns out to be essential for gastrulation in all animals in which it occurs.
5. All cnidarians are acoelomate.
A) 1 only
B) 1 and 4
C) 2 and 3
D) 2 and 4
E) 4 and 5

B

Concept 32.4
Skill: Synthesis/Evaluation
73) Some researchers claim that sponge genomes have homeotic genes, but no Hox genes. If true, this finding
would
A) strengthen spongesʹ evolutionary ties to the eumetazoa.
B) mean that sponges must no longer be classified as animals.
C) confirm the identity of sponges as ʺbasal animals.ʺ
D) mean that extinct sponges must have been the last common ancestor of animals and fungi.
E) require sponges to be reclassified as choanoflagellates.

C

Concept 32.4
Skill: Application/Analysis
Table 32.1. Proposed Number of Hox Genes in Various Extant and Extinct Animals
Last Common
Ancestor of Bilateria
Last Common Ancestor
of Insects and
Vertebrates
Ancestral Vertebrates Mammals
4 7 14 38-4
74) What conclusion is apparent from the data in Table 32.1?
A) Land animals have more Hox genes than do those that live in water.
B) All bilaterian phyla have had the same degree of expansion in their numbers of Hox genes.
C) Acoel flatworms should be expected to contain 7 Hox genes.
D) The expansion in number of Hox genes throughout vertebrate evolution cannot be explained merely by
three duplications of the ancestral vertebrate Hox cluster.
E) Extant insects all have 7 Hox genes.

D

Concept 32.4
Skill: Application/Analysis
75) All things being equal, which of these is the most parsimonious explanation for the change in number of Hox
genes from the last common ancestor of insects and vertebrates to ancestral vertebrates, as shown in Table 32.1?
A) The occurrence of 7 independent duplications of individual Hox genes.
B) The occurrence of 2 distinct duplications of the entire 7-gene cluster, followed by the loss of one cluster.
C) The occurrence of a single duplication of the entire 7-gene cluster.

C

Concept 32.4
Skill: Application/Analysis
Page 20
76) Two competing hypotheses to account for the increase in the number of Hox genes from the last common
ancestor all bilaterians to the last common ancestor of insects and vertebrates are: (1) a single duplication of the
entire 4-gene cluster, followed by the loss of one gene, and (2) 3 independent duplications of individual Hox
genes. To prefer the first hypothesis on the basis of parsimony requires the assumption that
A) the duplication of a cluster of four Hox genes is equally likely as the duplication of a single Hox gene.
B) there is an actual process by which individual genes can be duplicated.
C) genes can exist is spatial groupings called ʺclusters.ʺ
D) clusters of genes can undergo disruption, with individual genes moving to different chromosomes during
evolution.

A

Concept 32.4
Skill: Synthesis/Evaluation
Self-Quiz Questions
1) Among the characteristics unique to animals is
A) gastrulation.
B) multicellularity.
C) sexual reproduction.
D) flagellated sperm.
E) heterotrophic nutrition.

A

Skill:
2) Which of the following was the least likely factor causing the Cambrian explosion?
A) the emergence of predator-prey relationships between animals
B) the accumulation of diverse adaptations, such as shells and different modes of locomotion
C) the movement of animals onto land
D) the evolution of Hox genes that controlled development
E) the accumulation of sufficient atmospheric oxygen to support the more active metabolism of mobile
animals

C

Skill:
3) Acoelomates are characterized by
A) the absence of a brain.
B) the absence of mesoderm.
C) deuterostome development.
D) a coelom that is not completely lined with mesoderm.
E) a solid body without a cavity surrounding internal organs.

E

Skill:
4) 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) a circulatory system.
D) true tissues.
E) mesoderm.

D

Skill:
Page 21
5) Which of these is a point of conflict between the phylogenetic analyses presented in Figures 32.10 and 32.11 of
your textbook?
A) the monophyly of the animal kingdom
B) the relationship of segmented taxa relative to nonsegmented taxa
C) that sponges are basal animals
D) that chordates are deuterostomes
E) the monophyly of the bilaterians

B

Skill:
6) What is the main basis for placing the arthropods and nematodes in the Ecdysozoa in one hypothesis of animal
phylogeny?
A) Animals in both groups are segmented.
B) Animals in both groups undergo ecdysis.
C) They both have radial, determinate cleavage, and their embryonic development is similar.
D) The fossil record has revealed a common ancestor to these two phyla.
E) Analysis of genes shows that their sequences are quite similar, and these sequences differ from those of
the lophotrochozoans and deuterostomes.

E