Answers to Open-Ended Questions
Hoefnagels Essentials 2/e
Chapter 17
Answers to Mastering Concepts Questions
17.1
1. What characteristics do all animals share?
Animals are multicellular, have cells without walls, are heterotrophs by ingestion, have a
blastula stage during development, and have cells embedded in an extracellular matrix.
2. When and in what habitat did animals likely originate?
Animals probably originated in the oceans in Precambrian times. Today’s major groups
of animals arose in the oceans during Precambrian and Cambrian times.
3. What features were used to build the animal phylogenetic tree?
Animal phylogeny is based on cell and tissue organization, the number of germ layers,
body symmetry and cephalization, and structures that arise during embryonic
development. Molecular sequences are also important.
4. What are the events of animal early embryonic development?
In embryonic development, the diploid zygote divides repeatedly by mitosis to form a
blastula, which (in most animals) folds to form the gastrula with either two or three germ
layers. These germ layers develop into the animal’s tissues and organs.
5. What are the two main types of digestive tracts?
The two main types of digestive tracts are incomplete and complete digestive tracts.
6. What advantages does segmentation confer?
Segmentation increases flexibility. In addition, segmentation allows for the development
of specialized body regions with unique functions.
17.2
1. How is a sponge’s body different from that of other animals?
A sponge’s body has specialized cell types but not true tissues, and it does not have a
digestive tract. Instead, water containing food particles flows through pores in the
sponge’s body.
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2. How is a sponge’s body adapted to its aquatic habitat and sessile life?
Sponges have hollow, porous bodies. This arrangement allows sponges to create a
constant flow of water through their body. As the water passes, the sponges acquire food
and oxygen and dispose of wastes. They also release sperm into the current, which may
reach the egg cells of nearby sponges.
3. Explain how the arrangement of cells in a sponge is adaptive to its feeding strategy.
The collar cells in the sponge body create a current of water through the animal’s pores.
The cells capture passing food particles from the water, digest them, and transfer organic
compounds to the amoebocytes of the body wall.
4. In what ways are sponges important?
Sponges participate in food webs by filtering organic particles out of water. Their
economic importance includes the anticancer and antimicrobial drugs that are derived
from them.
17.3
1. What features do all cnidarians share?
All cnidarians have radial symmetry and incomplete digestive tracts. They are named for
their stinging cells.
2. Compare and contrast a polyp and a medusa.
Both body forms are radially symmetrical and have a mouth surrounded by tentacles. A
polyp is a sessile, tentacles-up body form. A medusa is the free-swimming, tentaclesdown body form.
3. How do cnidarians feed, move, and reproduce?
Feeding: Cnidarians are carnivores that feed by catching prey with their tentacles,
stinging it with cnidocytes, and stuffing it into their mouths. Movement: Some cnidarians
are sessile, remaining attached to a substrate. Medusas move by contracting muscles that
force water out of the bell. Reproduction: Cnidarians reproduce sexually and asexually.
4. In what ways are cnidarians important?
Cnidarians participate in aquatic food webs. Because cnidarians sting humans they are
economically important to tourism. Coral reefs protect coastlines from erosion and store
carbon dioxide in calcium carbonate. Coral reefs also protect many species of fishes,
invertebrates, and other animals.
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17.4
1. What features do all flatworms share?
All flatworms have bilateral symmetry, flattened bodies, and incomplete digestive tracts.
2. How does the body shape of a flatworm enhance gas exchange?
The flat body shape of a flatworm maximizes the surface area in contact with the
environment.
3. How do flatworms eat, move, and reproduce?
Free-living flatworms are carnivores and scavengers that eat organic matter, which they
acquire through their pharynx. Tapeworms attach to their host’s intestine and absorb food
through the body wall. Flatworms move by contracting muscles against a hydrostatic
skeleton. Flatworms reproduce asexually by pinching in half; they can also reproduce
sexually inside a host by producing eggs that are dispersed.
4. In what ways are flatworms important?
Flatworms participate in terrestrial and aquatic food webs, but their primary importance
to humans is that they cause infections that affect hundreds of millions of people as well
as domesticated and wild animals.
17.5
1. What adaptations do mollusks have in common?
Mollusks have a mantle that secretes a shell in most species, a muscular foot that
provides movement, a visceral mass containing the internal organs, and a radula.
2. How do mollusks feed, move, and protect themselves?
Mollusks feed by filtering organic particles out of the water; by scraping algae off rocks;
or by hunting prey. Mollusks move by contracting muscles against a hydrostatic skeleton.
Many mollusks protect themselves with a hard shell; others can evade predators by
changing color and darting away, often in a cloud of ink.
3. In what ways are mollusks important?
Besides their roles in terrestrial and aquatic food webs, mollusks are also important as
human food sources, although they can accumulate toxins from the surrounding water.
Snails and slugs damage and consume crops and garden plants. Introduced species such
as zebra mussels damage the ecology of lakes in the central United States.
17.6
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1. What features do all annelids share?
Annelids are segmented worms with bilateral symmetry and a complete digestive tract.
2. List examples of animals in each of the two classes of annelids.
Earthworms and leeches are in one group and the polychaetes (marine segmented worms)
are in the other group.
3. How do annelids feed, exchange gases, and move?
Earthworms consume organic matter; leeches suck blood or consume small invertebrates.
Gas exchange occurs at gills in polychaetes have gills and across the body wall for
leeches and earthworms. Annelids move by contracting circular and longitudinal muscles
that surround the fluid-filled coelom. Polychaetes swim with their paddlelike appendages.
17.7
1. What features do all roundworms share?
Roundworms, also known as nematodes, are unsegmented, cylindrical worms with
tapered ends and a complete digestive tract.
2. Contrast the bodies of roundworms, flatworms, and annelids.
Roundworms have a pseudocoelom, compared to the true coelom of annelids and the
absence of any coelom in flatworms. Roundworms have cylindrical, unsegmented bodies,
compared to the segmented bodies of annelids and the flat bodies of flatworms. All types
of worms have bilateral symmetry.
3. How do nematodes feed and move?
Nematodes eat fungi, bacteria, roots, or almost any other plant part. They also parasitize
mammals by sucking blood or consuming digested food. Nematodes move by contracting
longitudinal muscles against the fluid-filled pseudocoelom. They have no circular
muscles, so they only thrash from side to side.
4. How are roundworms important?
Roundworms are extremely numerous and therefore participate in the food webs of every
habitat. However, they are also parasites of humans, other animals, and crop plants.
Caenorhabditis elegans is an important model organism used in biological research.
17.8
1. What features distinguish the arthropods?
Arthropods have an exoskeleton, jointed appendages, and segmentation.
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2. How do arthropods use their jointed appendages?
Arthropods use their jointed appendages for movement, defense, prey capture, sensing
the environment, ornaments, weapons, and copulation.
3. Describe how arthropods feed, respire, excrete metabolic wastes, sense their
environment, move, reproduce, and defend themselves.
Arthropods feed on almost every imaginable inorganic substance, either by chewing or
sucking. On land, arthropods exchange gases via tubules called tracheae or via book
lungs; arthropods that live in water respire with gills. Arthropods have specialized organs
that remove nitrogenous wastes, which are deposited into the end of the digestive tract
and ejected though the anus. Arthropods have specialized sense organs that are sensitive
to light, sound, scents, chemicals, potential mates, food proximity, touch, air currents, and
body position. Arthropods move by contracting muscles attached internally to the
exoskeleton. Although there are asexually reproducing species, most arthropods
reproduce sexually, using internal fertilization. The exoskeleton offers some protection
against predators, but many arthropods defend themselves by fleeing, biting, stinging,
pinching, making noises, or giving off foul odors. Camouflage is another defense, as are
wing spots that may startle predators.
4. What is the function of the exoskeleton?
The main functions of the exoskeleton are protection and movement.
5. In what ways are arthropods important?
Arthropods are extremely numerous and play important roles in food webs. They are
important pollinators of crops. They also spread diseases, sting people, and destroy crops
and wooden structures. They make honey, silk, and beeswax, and people eat shrimp,
lobsters, crabs, and crayfish.
6. How are chelicerates different from mandibulates?
The difference is in the mouthparts. Chelicerates have clawlike chelicerae, whereas
mandibulates have jawlike mandibles.
17.9
1. What characteristics distinguish the echinoderms?
Echinoderms have a spiny skin, and adults have a radially symmetrical body divided into
five parts. Larvae have bilateral symmetry. The echinoderms also have a water vascular
system.
2. What is a water vascular system and why is it adaptive?
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A water vascular system is a system of internal canals connected to hollow, suction cuplike feet, which create a firm grip on the substrate. Pumping water into and out of each
tube foot extends and retracts it, allowing echinoderms to move while also holding tight
to the substrate. Natural selection has modified the water vascular system in many other
ways that promote reproductive success, including gas exchange, elimination of
metabolic wastes, sensing the environment, and feeding.
3. In what ways are echinoderms important?
Besides their roles in marine food webs, echinoderms are also important in that some
people eat them, and some can sting humans. Some sea stars, like the crown of thorns sea
star, harm coral reefs.
17.10
1. What are four key defining characteristics of chordates?
Four of the defining features of chordates are: a notochord; a dorsal, hollow nerve cord;
pharyngeal pouches or slits; and a postanal tail.
2. Which chordates have a cranium, and which are also vertebrates?
All chordates except tunicates and lancelets have a cranium. Vertebrates include
lampreys, fishes, amphibians, reptiles, and mammals.
3. How did the origin of jaws, lungs, limbs, and the amnion affect the course of vertebrate
evolution?
Jaws enabled animals to exploit new food sources. Lungs allowed vertebrates to move
out of water and onto land, obtaining O2 from air. Limbs allowed vertebrates to walk on
land and expanded their ecological roles. The amnion allowed animals to reproduce on
land instead of in water.
4. What is the difference between an ectotherm and an endotherm?
The body temperature of an ectotherm varies with the environment, but can be altered by
behaviors such as basking in the sun. In contrast, the body temperature of an endotherm
is maintained at a steady level by metabolic processes and physiological mechanisms
(such as shivering, panting, and sweating).
17.11
1. What is the relationship among tunicates, lancelets, and the vertebrate chordates?
The tunicates and lancelets are two lineages of simple chordates; they may resemble the
last common ancestor shared by all chordates, including the vertebrates.
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2. Make a table comparing the features of each vertebrate group.
Answers will vary but should include the main characteristics of lampreys, fishes,
amphibians, reptiles, and mammals. Use the “Key features” evolutionary trees in section
17.11 as well as figure 17.40 as references.
3. Describe the adaptations that mark the transition from fishes to amphibians, reptiles,
and mammals.
The transition from fishes to amphibians, reptiles, and mammals is characterized by
adaptations to life on land. Lungs enable gas exchange with the air. Limbs allow
locomotion on land. The amnion (which is only in reptiles and mammals) enables
reproduction away from water.
4. What characteristics place the birds within the reptiles, and how are birds different
from other reptiles?
Birds have amniotic eggs and skeletons that are similar to those of nonavian reptiles. The
presence of feathers on some dinosaurs is another shared characteristic. Birds are
different from other reptiles because of endothermy and their adaptations to flight.
17.12
1. Name the three groups of contemporary primates. To which group do humans belong?
The three groups of contemporary primates are prosimians (lemurs and their relatives),
monkeys, and hominoids (apes). Humans are hominoids.
2. What can skeletal anatomy and DNA sequences in existing primates tell us about
human evolution?
The skeletal anatomy of existing primates can help us understand trends in human
evolution, including the diets, body positions, sizes, and many other aspects of fossil
humans and their ancestors. DNA sequences in existing primates can reveal which
species are most closely related to one another and to humans.
3. What are the four groups of species in the hominin family tree, and which still exist
today?
The four groups are Ardipithecus, Australopithecus, Paranthropus, and Homo. Only
Homo sapiens exists today.
4. Which conditions may have contributed to the evolution of humans?
Conditions that led to the origin of humans are rooted in plate tectonics. After India and
the Himalayan region collided with Eurasia, the rise of the Himalayas altered Africa’s
climate. It became cooler and some tropical forests became grasslands. Ancestors of
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humans began to live in grasslands instead of in trees; the new habitat selected for the
bipedalism that characterizes humans. The degree of exposure to ultraviolet radiation has
selected for different skin colors; migration and culture have also affected human
evolution.
Write It Out
1. Compare the nine major animal phyla in the order in which the chapter presents them,
listing the new features for each group.
Sponges – multicellularity; Cnidarians – tissues and two germ layers; Flatworms –
bilateral symmetry, three germ layers, protostome, incomplete digestive tract; Mollusks –
mantle, complete digestive tract, coelom; Annelids – segmentation; Roundworms –
pseudocoelom; Arthropods – exoskeleton, jointed appendages; Echinoderms –
deuterostome, water vascular system; Chordates – notochord, hollow nerve cord,
pharyngeal slits, postanal tail.
2. Suppose you watch a video showing the development of an unknown animal. What
clues can the developmental pattern give you about how this organism is classified?
Creating a flow chart might be useful.
If gastrulation does not occur, then the animal is a sponge. If gastrulation does occur, but
no mesoderm develops after gastrulation, then the animal is probably a cnidarian. If a
mesoderm does develop, then the organism will be bilaterally symmetrical. Continue
watching the first indentation formed at gastrulation. If it eventually develops into the
organism’s mouth, then it is a protostome (such as a flatworm, mollusk, annelid,
roundworm, or arthropod). If the first indentation of the gastrula develops into the
organism’s anus, then the organism is a deuterostome (such as a chordate or an
echinoderm).
3. Using the evolutionary trees in this chapter, compare the following groups. For each
comparison, what features are similar among the groups? What features are different?
(a) Compare cnidarians to sponges and to the clade containing flatworms, mollusks, and
annelids.
(b) Compare flatworms to cnidarians, other protostomes, and deuterostomes.
(c) Compare mollusks to flatworms and annelids.
(d) Compare nematodes to other protostomes in general and to arthropods in particular.
(e) Compare echinoderms to protostomes and to chordates.
(a) All animals are multicellular, so all five phyla share that characteristic. Unlike
sponges, cnidarians have true tissues. Annelids, mollusks, and flatworms have bilateral
symmetry and three germ layers, whereas cnidarians have radial symmetry and two germ
layers.
(b) Cnidarians are similar to flatworms in that both groups have true tissues and
multicellularity. However, cnidarians are radially symmetrical and only have two germ
layers. Flatworms have bilateral symmetry and three germ layers; other protostomes and
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all deuterostomes share these features. During the development of flatworms and other
protostomes, the first opening to form in the gastrula typically becomes the mouth; in
deuterostomes, this opening becomes the anus. Features unique to flatworms include a
flattened body with no coelom.
(c) Mollusks have a mantle that secretes a shell in most species, a muscular foot that aids
in movement, and a visceral mass containing the internal organs. Mollusks, flatworms,
and annelids are all protostomes with bilateral symmetry, three germ layers, and
multicellularity.
(d) Like all protostomes, nematodes are multicellular animals with bilateral symmetry
and three germ layers. Arthropods and nematodes form a clade of molting animals. A
pseudocoelom is unique to nematodes.
(e) During development, the first opening to form in an echinoderm gastrula becomes the
anus; echinoderms are therefore deuterostomes and not protostomes. Echinoderms have
unique characteristics (spiny skin, radial symmetry as adults, and the water vascular
system) that differentiate them from the chordates.
4. List the criteria used to distinguish: (a) animals from other organisms; (b) vertebrates
from invertebrates; (c) protostomes from deuterostomes; (d) ectotherms from
endotherms.
(a) Animals are multicellular, eukaryotic, heterotrophic organisms that do not possess cell
walls. Animals undergo a unique embryological development, and their cells secrete and
bind to a nonliving substance known as the extracellular matrix.
(b) Vertebrates possess backbones; invertebrates do not.
(c) In protostomes, the first indentation of the gastrula forms the mouth; in
deuterostomes, the first indentation forms the anus.
(d) In general, an ectotherm’s body temperature fluctuates with the external environment;
endotherms typically maintain a more constant internal body temperature.
5. Compare the digestive tract of an earthworm and a flatworm. How is each worm’s
digestive system adaptive?
An earthworm has a complete digestive tract, with a mouth and anus. Food moves in one
direction through the digestive tract, boosting the efficiency of digestion. Blood delivers
the nutrients to each segment. In contrast, flatworms have an incomplete digestive tract
with only one opening. The highly branched digestive system delivers nutrients to
directly to cells.
6. Analyze the evolutionary tree in figure 17.3, and then write an argument supporting or
refuting this statement: Annelids are more closely related to flatworms than to
roundworms.
This statement is true. Annelids and flatworms share a clade (Lophotrochozoa) with
mollusks, whereas roundworms are in a clade (Ecdysozoa) with arthropods. Even though
annelids and roundworms are next to each other on the tree, the close proximity of two
taxa at the tips of a tree does not necessarily imply a close evolutionary relationship.
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Instead, the evolutionary relatedness of two taxa is determined by tracing the lineages
(the lines of the tree) backward from the tree’s tips to where those lineages intersect.
7. Segmented animals occur in multiple phyla. How might segmentation benefit an
animal? If segmentation is adaptive, why do unsegmented animals still exist?
Segmentation occurs in the annelids, arthropods, and chordates, adding flexibility and
offering new opportunities for developing specialized body parts. Unsegmented animals
exist either because segmentation never arose in a lineage or because segmentation was
not adaptive in those animals’ environments. In many habitats, unsegmented animals still
have reproductive success.
8. Create lists of animal phyla that (a) are cephalized, (b) have an incomplete digestive
tract, (c) have segmented bodies, and (d) have a coelom.
Cephalized animals include annelids, roundworms, flatworms, arthropods, some
mollusks, and chordates. Cnidarians and flatworms have an incomplete digestive tract.
Segmented bodies occur in annelids and arthropods; chordates also have a segmented
body, but the divisions are much less obvious. Mollusks, annelids, arthropods,
echinoderms, and chordates have a coelom; nematodes have a pseudocoelom.
9. Both amniotes and insects do very well on land. What characteristics are found in both
groups that facilitate their success in terrestrial environments?
Overall, the body plans of insects and amniotes are versatile enough to enable the
development of specialized structures that promote reproductive success on land. For
example, both groups have a skeletal and muscular system that can support the animal’s
weight outside of the water. They also have structures that prevent developing embryos
from drying out, so they can reproduce away from water.
10. What are four distinguishing characteristics of chordates?
Chordates have a notochord, a dorsal hollow nerve cord, pharyngeal slits or pouches, and
a postanal tail.
11. Draw from memory a phylogenetic tree that traces the evolutionary history of
vertebrates. Include the features that mark each branching point in your tree.
Answers will be visual and based on figure 17.21, but here are some examples of what
the tree should include. Fishes with lung precursors, a body skeleton, and limbs gave rise
to the amphibians, which straddle the land-water transition. Some amphibians gave rise
to reptiles, which have additional adaptations to dry land (including waterproof skin and
an amniote egg). Different branches of reptiles eventually gave rise to modern birds
(which have feathers) and mammals (which have hair and mammary glands).
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12. Tunicates look much different than other chordates. Why are they classified in the
same phylum?
The tunicates have all four chordate characteristics during the larval stage.
13. List the evidence that biologists use to classify earthworms, caecilians, and snakes in
different clades despite the superficial similarities between these animals.
An earthworm is an annelid (a segmented worm); it is an invertebrate. Caecilians and
snakes are vertebrate chordates, but a caecilian is a limbless amphibian, whereas a snake
is a limbless reptile. Unlike caecilians, snakes are amniotes.
14. List three adaptations that enable fishes to live in water, amphibians to live on land,
snakes to live in the desert, and birds to fly.
Fishes: gills, paired fins, lateral line. Amphibians: lungs, limbs, denser skeleton
(compared to fishes). Snakes: scales, internal fertilization, amniote eggs. Birds: feathers,
tapered bodies, hollow bones.
15. How does the changing placement of birds in the vertebrate family tree illustrate the
scientific process? Why does this type of research matter?
Scientific hypotheses and theories change to incorporate new data; the emerging evidence
of the similarities between reptiles and birds resulted in changes in the phylogenetic tree.
Refining these relationships helps us to better understand the evolutionary process and
the history of life.
16. How are fishes, amphibians, nonavian reptiles, birds, and mammals important to
humans? How are they important in ecosystems?
Other vertebrates are important to humans because they provide a source of enjoyment,
food, and commercial products. Also these animals provide humans with a better
understanding of life on Earth. They also play essential roles in ecosystem function such
as indicators of environmental quality or predators that control prey populations.
17. Among plants and vertebrates, some species are well-adapted to dry land, whereas
others require moisture to reproduce. Compare and contrast the adaptations in plants and
vertebrates that have allowed each group to breed in increasingly dry habitats.
Mosses and ferns have swimming sperm and require moisture to reproduce, but the
flowering plants have pollen and seeds that enable reproduction in the driest habitats.
Likewise, aquatic animals depend upon water for the dispersal of sperm, whereas
terrestrial vertebrates use internal fertilization. Unlike mosses and ferns, flowering plants
protect their embryos inside a tough seed coat. Likewise, the amnion protects the
embryos of reptiles and mammals.
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18. If the success of an animal group is determined by the number of species it contains,
how successful are mammals compared to other chordate classes? How successful are
mammals compared to insects? Hint: See figures 17.38 and 17.40.
Mammals contain about 5800 species, outnumbering only the lampreys, hagfishes, and
tunicates. Insects contain at least a million species. Considering only the number of
species in each animal group, mammals are not nearly as successful as many other
groups.
19. Explain how a sessile or slow-moving lifestyle, such as that of sponges, sea
cucumbers, and tunicates, might select for bright colors and an arsenal of toxic chemicals.
A soft-bodied sessile or slow-moving animal is extremely vulnerable to predators. Those
that produce toxins and warning coloration are likely to have greater reproductive success
than those that do not.
20. Biologists have speculated that the first feathered dinosaurs may have used feathers in
mating displays, to conserve body heat, or in flight. How might you use fossils, living
species, or both to test each hypothesis?
You could begin with detailed observations of the fossilized feather impressions in the
earliest feathered dinosaurs. You could measure the dimensions of the feather, the
number of feathers, or the percentage of body area covered by feathers. Next you could
observe the same variables in existing species that use feathers for mating displays,
conserving body heat, and flight. Initial conclusions could be based on the modern
species with variables most similar to the earliest feathered dinosaurs.
21. Invasive animal species are disrupting ecosystems around the world. Search the
Internet for a list of invasive animal species in your state. What phyla are represented in
the list? What harm do they do? How important do you think it is to try to eradicate
invasive species?
[Answers will vary].
22. What can scientists learn by comparing the fossilized skeletons of extinct primates
with the bones of modern species?
The fossilized skeletons can yield important information regarding locomotion, posture,
diet, and brain size.
23. The foramen magnum in Australopithecus africanus is closer to the front of the skull
than in gorillas. What does this observation indicate about A. africanus?
This shows that the spinal cord in Australopithecus africanus was oriented under the head
like it is in humans and other bipedal species.
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24. In what ways has culture been an important factor in human evolution?
Culture has facilitated the development of language, art, agriculture, and many other
human characteristics. The ability to transmit knowledge from generation to generation
has enabled us to learn from the past and has contributed greatly to our success as a
species.
25. At one time, several species of Homo existed at the same time. Propose at least two
hypotheses that might explain why only Homo sapiens remains.
Perhaps Homo sapiens had greater intelligence and, therefore, greater reproductive
success than the other species. Perhaps Homo sapiens interbred with the other species,
eliminating the distinctions among them. Perhaps Homo sapiens killed off the other
species.
26. How do you predict a scientist would respond to a question about whether humans
“evolved from monkeys”?
Humans did not “evolve” from monkeys. Humans do share a common ancestor with
monkeys (indeed, with all primates), but monkeys are not our closest relatives.
Chimpanzees are our closest relatives, but a chimp did not turn into a human. Instead, a
population of ancestral apes diverged into chimpanzees, humans, and other extinct and
existing lineages.
27. Compare the timelines illustrated in figures 16.2 and 17.1. Speculate on some ways
that changes in land plants might have driven animal evolution, and vice versa.
Plants moved onto land about 35 million years before the first invertebrates moved out of
the water. Vascular tissue, which gave rise to larger land plants, arose 55 million years
before vertebrates moved on to land. Pollen and seeds, which allowed plants to reproduce
away from water, arose 35 million years before the reptiles (the first vertebrates to
reproduce away from water). Plants moving from water to increasingly dry land opened
up new habitats and food sources for animals. Likewise, plants that could avoid herbivory
had a selective advantage. Much later, many types of plants began to rely on hungry
animals to disperse pollen and seeds.
Pull It Together
1. Write connecting phrases to separate arthropods and roundworms from annelids,
mollusks, and flatworms.
“Protostomes” could connect with “grouped as ecdysozoans and that periodically molt
are” to “Arthropods” and “Roundworms”. “Protostomes” could also connect with
“grouped as lophotrochozoans based on DNA sequences include” to “Annelids”,
“Mollusks”, and “Flatworms”.
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2. Write connecting phrases to separate echinoderms from chordates.
Many answers are possible. For example, echinoderms lack cephalization, and chordates
have a notochord.
3. Draw a concept map that summarizes the chordates, including both invertebrates and
vertebrates.
One possible way to construct the concept map would be to draw two branches from the
word “Chordates.” A branch labeled “without backbones” would include invertebrates,
which in turn would lead to tunicates, lancelets, and hagfishes. A branch labeled “with
backbones” would include vertebrates, which in turn would lead to lampreys, fishes,
amphibians, reptiles, and mammals.
4. Add tunicates, hagfishes, birds, monotremes, vertebrates, marsupials, and placental
mammals to this concept map.
A branch from “Chordates” labeled “without backbones” would include the “Tunicates”
and the “Hagfishes”. A branch from “Chordates” labeled “with backbones” would
connect to “Vertebrates”, which in turn could connect with “include” to “Birds” and
“Mammals”. Within the “Mammals” you could indicate the egg-laying “Monotremes”,
pouched “Marsupials”, and “Placental Mammals” (which retain the young inside the
female’s body).
5. Which animals are aquatic and which are terrestrial? What advantages were gained by
the first organisms to leave the water?
The sponges, cnidarians, echinoderms, and fishes are all aquatic groups. All other groups
have some aquatic and some terrestrial forms. The first organisms to leave the water
were able to exploit new and more varied resources. The first groups on land also had
fewer predators until a terrestrial existence became more widespread.
6. Other than the ones pictured, give an example of a species in each phylum.
[Answers will vary].
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