44) According to the phylogenies depicted in the previous pair of figures, if one were to create a taxon
called Radiata 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) More than one of these responses are correct.
45) What is true of the deuterostomes in the molecular phylogeny (B) that is not true in the traditional
phylogeny (A)?
A) Deuterostomia is a clade.
B) To maintain Deuterostomia 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.
46) In the traditional phylogeny (A), 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 (B), 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) Platyhelminthes’ close genetic ties to the arthropods became clear as their Hox gene sequences were
studied.
Placozoan evolutionary relationships to other animals are currently unclear, and different phylogenies
can be created, depending on the character used to infer relatedness. Sponges have no tissues, but about
20 cell types. Tp (Trichoplax adhaerens) produces a neuropeptide almost identical to one found in
cnidarians. The genome of Tp, though the smallest of any known animal, shares many features of
complex eumetazoan (even human!) genomes. The next three questions refer to the phylogenetic trees
that follow.
I II
III
47) Which phylogeny has been created by emphasizing genomic features of placozoans?
A) I
B) II
C) III
48) Which phylogeny has been created by emphasizing the structural simplicity of placozoans?
A) I
B) II
C) III
49) Which phylogeny has been created by emphasizing a protein found in placozoans?
A) I
B) II
C) III
Scenario Questions
50) Cycliophorans have two types of larvae. One type of larva the Prometheus larva develops into a
male. The male, which lacks a digestive system, attaches to the outside of a feeding stage (a female) and
impregnates her digestive system, which develops into a different type of larva. What must be true of the
digestive system of the feeding-stage female while she is still a virgin?
1. At least some of its cells are haploid.
2. It consists only of highly specialized cells.
3. It is the same size as the male.
A) 1 only
B) 2 only
C) 3 only
D) 1 and 3
E) 2 and 3
Trichoplax adhaerens (Tp) is the only living species in the phylum Placozoa. Individuals are about 1
mm wide and only 27 μm high, are irregularly shaped, and consist of a total of about 2,000 cells, which
are diploid (2n = 12). There are four types of cells, none of which are nerve or muscle cells, and none of
which have cell walls. They move using cilia, and any “edge” can lead. Tp feeds on marine microbes,
mostly unicellular green algae, by crawling atop the algae and trapping it between its ventral surface and
the substrate. Enzymes are then secreted onto the algae, and the resulting nutrients are absorbed. Tp
sperm cells have never been observed, nor have embryos past the 64-cell (blastula) stage.
51) If Tp sperm are observed by future researchers, how many chromosomes should be found in a Tp
sperm nucleus?
A) 2
B) 3
C) 6
D) 12
52) In how many of the following ways is Tp unlike the typical animal?
1. Tp is multicellular.
2. Tp lacks muscle and nerve cells.
3. Tp has cilia.
4. Tp has a different place where digestion of food occurs.
5. Tp lacks cell walls.
A) only one way
B) two ways
C) three ways
D) four ways
E) all five ways
53) On the basis of information in the previous paragraph, which of these should be able to be observed
in Tp?
A) the act of fertilization
B) the process of gastrulation
C) eggs
D) All three of the responses above are correct.
E) Two of the responses above are correct.
54) In its native environment, a Tp cell neither gains nor loses water. What should one expect to occur
when Tp is placed into fresh water?
A) no change from the above, as fresh water is its native environment
B) lysis
C) plasmolysis
D) slight shrinkage
55) Tp’s body symmetry seems to be most like that of
A) most sponges.
B) cnidarians.
C) worms.
D) tetrapods.
E) Two of the responses above are correct.
56) In an experiment, several Tp individuals were stained different colors. The stained individuals were
then passed through a strainer, disaggregated to the level of single cells, and collected into a common
container of seawater. Which subsequent finding would be most surprising if the Tp individuals used in
this experiment had been produced by sexual, rather than asexual, means?
A) If all of the cells from a given individual reaggregated to form the same individual, and if each cell
had retained its original identity, as far as cell type goes.
B) If all of the cells from a given individual reaggregated to form the same individual, but if each cell
had a different identity than it had before disaggregation.
C) If cells from different original individuals reaggregated together to form new individual organisms.
D) If cells from different original individuals reaggregated together to form new species.
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 to lie in the grooves between larger,
underlying cells (i.e., spiral cleavage).
57) This embryo may potentially develop into a(n)
A) turtle.
B) earthworm.
C) sea star.
D) fish.
E) sea urchin.
58) 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 a nonviable 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.
The most recently discovered phylum in the animal kingdom (1995) is the phylum Cycliophora. It
includes three species of tiny organisms that live in large numbers on the outsides of the mouthparts and
appendages of lobsters. The feeding stage permanently attaches to the lobster via an adhesive disk, and
collects scraps of food from its host’s feeding by capturing the scraps in a current created by a ring of
cilia. The body is sac-like and has a U-shaped intestine that brings the anus close to the mouth.
Cycliophorans are eucoelomate, do not molt (though their host does), and their embryos undergo spiral
cleavage.
59) Which of these features is least useful in assigning the phylum Cycliophora to a clade of animals?
A) having a true coelom as a body cavity
B) having a body symmetry that permits a U-shaped intestine
C) having embryos with spiral cleavage
D) lacking ecdysis (molting)
60) Basing your inferences on information in the previous paragraph, to which clade(s) should
cycliophorans belong?
1. Eumetazoa
2. Deuterostomia
3. Bilateria
4. Ecdysozoa
5. Lophotrochozoa
A) 1 only
B) 1 and 3
C) 1, 3, and 5
D) 2, 3, and 4
E) 2, 3, and 5
61) If harboring large populations of cycliophorans neither helps nor harms their lobster hosts, then
cycliophorans can be properly considered to be
1. parasites.
2. mutualists.
3. commensals.
4. symbionts.
5. endosymbionts.
A) 1 and 4
B) 2 and 4
C) 3 and 4
D) 2 and 5
E) 3 and 5
62) On the basis of the cleavage pattern of cycliophoran embryos, which of these should be true?
A) It has determinate development.
B) The blastopore becomes the anus.
C) They are deuterostomes.
D) A cell separated from a four-cell embryo should develop into a complete organism.
63) Using similarities in embryonic development, body symmetry, and other anatomical features to
assign an organism to a clade involves
1. cladistics based on body plan.
2. molecular-based phylogeny.
3. morphology-based phylogeny.
A) 1 only
B) 2 only
C) 3 only
D) 1 and 2
E) 1 and 3
64) Which of these, if discovered among cycliophorans, would cause the most confusion concerning our
current understanding of cycliophoran taxonomy?
A) if the ciliated feeding ring is a lophophore
B) if embryos are diploblastic
C) if the body cavity is actually a pseudocoelom
D) if the organisms show little apparent cephalization
65) What is true of the feeding stage of cycliophorans?
1. It is chemoheterotrophic.
2. It is sessile.
3. It captures food in a manner similar to that of animals with lophophores.
4. It has radial symmetry.
A) 1 and 2
B) 1 and 3
C) 2 and 4
D) 1, 2, and 3
E) 2, 3, and 4
66) Cycliophorans have two types of larvae. One type of larva is produced when the digestive system of
a female is impregnated by a male. The digestive system then collapses and develops into a larva, which
swims away in search of a new host after the surrounding female dies. Which is the embryonic tissue
that is apparently most important in forming this type of larva?
A) mesohyl
B) mesoderm
C) ectoderm
D) endoderm
E) mesoglea
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
38-40
67) What conclusion is apparent from the data in the table?
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 seven 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 seven Hox genes.
68) All things being equal, which of these is the most parsimonious explanation for the change in the
number of Hox genes from the last common ancestor of insects and vertebrates to ancestral vertebrates,
as shown in the table?
A) The occurrence of seven independent duplications of individual Hox genes.
B) The occurrence of two distinct duplications of the entire seven-gene cluster, followed by the loss of
one cluster.
C) The occurrence of a single duplication of the entire seven-gene cluster.
69) Two competing hypotheses to account for the increase in the number of Hox genes from the last
common ancestor of bilaterians to the last common ancestor of insects and vertebrates are: (1) a single
duplication of the entire four-gene cluster, followed by the loss of one gene, and (2) three 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 clusters.
D) clusters of genes can undergo disruption, with individual genes moving to different chromosomes
during evolution.
End-of-Chapter Questions
The following questions are from the end-of–chapter “Test Your Understanding” section in Chapter 32
of the textbook.
70) Among the characteristics unique to animals is
A) gastrulation.
B) multicellularity.
C) sexual reproduction.
D) flagellated sperm.
E) heterotrophic nutrition.
71) 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.
72) 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.
73) Which of the following was probably the least important factor in bringing about the Cambrian
explosion?
A) the emergence of predator-prey relationships among animals
B) the accumulation of diverse adaptations, such as shells and different modes of locomotion
C) the movement of animals onto land
D) the origin of Hox genes and other genetic changes affecting the regulation of developmental genes
E) the accumulation of sufficient atmospheric oxygen to support the more active metabolism of mobile
animals
24
74) Which of the following is a point of conflict between the phylogenetic analyses presented in these
two figures?
A) the monophyly of the animal kingdom
B) the relationship of taxa of segmented animals to taxa of nonsegmented animals
C) that sponges are basal animals
D) that chordates are deuterostomes
E) the monophyly of the bilaterians