CHAPTER 32: OVERVIEW OF ANIMAL DIVERSITY
WHERE DOES IT ALL FIT IN?
Chapter 32 takes the same strategy as Chapters 27 through 31 and highlights the diversity of animals.
Students should be encouraged to recall the principles of eukaryotic cell structure and evolution
associated with the particular features of animal cells. Multicellularity should also be reviewed. The
information in chapter 32 does not stand alone. Students should know that animals and other
organisms are interrelated and originated from a common ancestor of all living creatures on Earth.
SYNOPSIS
Animals are distinctly different from other life forms studied thus far. They are multicellular,
heterotrophic, have no cell walls, move rapidly and in complex ways, are diverse in form and
habitat, exhibit primarily sexual reproduction, undergo embryonic development, and have unique
tissues. The animal kingdom is divided into two subkingdoms: Parazoa (beside animals) and
Eumetazoa (true animals). Both are derived from the same unicellular choanoflagellate ancestor.
Sponges are the most familiar parazoans; they are typically asymmetrical and lack both tissues
and organs. The 35 phyla of eumetazoans possess definite shape, symmetry and tissues that are
organized into organs and organ systems. The Eumetazoans are further divided into Radiata
(diploblastic), animals with radial symmetry and two tissue layers of ectoderm and endoderm;
and, Bilateria (triploblastic), animals with bilateral symmetry and three tissue layers of ectoderm,
mesoderm, and endoderm. The bilateral animals are split further into groups based on other
characteristics.
Animal phyla show five key transitions in body plan as they evolve from simple to more
complex forms. First, there was the evolution of tissues from no defined tissues and organs to
distinct tissues with highly specialized cells. The sponges lack tissues; all other animals possess
tissues. Second, there was the evolution of symmetry-asymmetry (animals with no defined
symmetry), radial symmetry (animals with body parts arranged around a central axis), and
bilateral symmetry (body design in which the body has a right and left halves). Porifera, the
sponges, are asymmetrical, lacking any kind of symmetry. Radiata (cnidarians and ctenophora)
exhibit radial symmetry while all other animals are bilaterally symmetrical. Bilateral symmetries
allows for the differential adaptation of various parts of the body. It also supports the evolution
of cephalization with the localization of sensory organs at one end. The third key transition is the
evolution of a body cavity. Three basic kinds of body plans evolved in the Bilateria: acoelom
(no body cavity), pseudocoelom (false body cavity located between the mesoderm and
endoderm), and coelom (fluid-filled true body cavity that develops entirely in the mesoderm).
Acoelomates like flatworms possess no body cavity and are commonly called solid-bodied
worms. Seven animal phyla are pseudocoelomates, possessing a pseudocoel, including the
roundworms found in phylum Nemotoda. Most members of the animal kingdom are coelomates.
The gut and other internal organs are suspended within the coelom. The advent of this type of
body cavity necessitated the development of a more complex circulatory system to ensure that all
organs receive oxygen and nutrients. The fourth transition separates protostome and deuterstome
development. Cleavage patterns differ as the protostomes undergo spiral cleavage and the
deuterstomes undergo radial cleavage. Additionally, in protostomes the blastopore becomes the
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mouth while in deuterostomes the blastopore becomes the anus. The evolution of segmentation is
the fifth key transition. Segmentation provides for more efficient locomotion and increased
protection from damage due to the replication of organs in each segment. True segmentation is
found in annelids, arthropods, and chordates.
The way animals are being classified is continually being reviewed and reevaluated. The current
scheme has been in existence for almost a century and has always presented problems with its
simplistic either/or organization. Now, new taxonomical comparisons using molecular data, the
field of molecular systematics uses unique genomic sequences to identify related groups, have
come to different conclusions. Morphological characters that have traditionally been used to
construct animal phylogenies—segmentation, coeloms, and jointed appendages—are not the
conservative characteristics as once believed.
It is believed and agreed that the animal kingdom is monophyletic, arising from a colonial
flagellated protist. Three prominent hypotheses for the origin of metazoans from protists include:
(1) multinucleate hypothesis suggesting that metazoans arose from a multinuclear protist;
(2) colonial flagellate hypothesis that states that metazoans descended from colonial protists;
and, (3) the polyphyletic origin hypothesis that proposes sponges evolved independently from
eumetazoans. Animal diversity exploded in the Cambrian and biologists still are debating what
caused this explosion. Some say it was the emergence of new body plans and innovations in
mobility and hunting success. Still others say it was a build up of dissolved oxygen and minerals
in oceans. A new field of “evo devo” looks at the evolutionary biology and developmental
biology changes. The development of Hox genes during the Cambrian era provides a tool that
can produce rapid changes in body plans.
LEARNING OUTCOMES
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Understand how the animals are organized and how this organization is different from that of
plants, fungi, protists, and prokaryotes.
Know the five key transitions in body plans.
Compare and contrast Parazoa and Eumetazoa in terms of evolution, complexity, symmetry, and
organization of embryonic cell layers.
Compare and contrast asymmetry, radial symmetry, and bilateral symmetry.
Differentiate among acoelomate, pseudocoelomate, and coelomate organisms; indicate how they
are evolutionarily related and give examples of each.
Understand the advantages of segmentation; give at least one example of segmentation in each of
the coelomate phyla.
Differentiate between protostomes and deuterostomes.
Compare the tradition methods using morphology in classification of animals to the new
molecular systematics using DNA and RNA analysis to classify related animal groups.
Review the theories behind the emergence of body plans.
Understand how Hox genes contributed to body changes.
Understand what happened during the Cambrian explosion.
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COMMON STUDENT MISCONCEPTIONS
There is ample evidence in the educational literature that student misconceptions of information
will inhibit the learning of concepts related to the misinformation. The following concepts
covered in Chapter 32 are commonly the subject of student misconceptions. This information on
“bioliteracy” was collected from faculty and the science education literature.
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Students do not understand the evolution of endosymbionts in animal cells
Students are unsure that many of the lower animals are classified as animals
Students think that all animals evolved at about the same time
Students believe that all animals are mobile
Students believe that most animals are vertebrates
Students believe that animals exclusively reproduce sexually
Students do not equate humans with being animals
Students believe that cells of protists and animals are almost identical in structure and
function
Students that animal classification is based on one linear line of evolution
Students believe that all animals have identical organ system structures
Students are unaware of molecular methods of animal classification
INSTRUCTIONAL STRATEGY PRESENTATION ASSISTANCE
Suggest that your students prepare charts indicating how various physiological functions occur in
each of the phyla presented in this and the next few chapters. Include nervous activities,
reproduction, respiration, digestion, excretion, circulation, and locomotion. This type of chart
makes it easier to see the functional and evolutionary relationships among the various phyla.
HIGHER LEVEL ASSESSMENT
Higher level assessment measures a student’s ability to use terms and concepts learned from the
lecture and the textbook. A complete understanding of biology content provides students with the
tools to synthesize new hypotheses and knowledge using the facts they have learned. The
following table provides examples of assessing a student’s ability to apply, analyze, synthesize,
and evaluate information from Chapter 32.
Application
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Have students describe similarities and differences between the metabolic
needs of animals and plants.
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Have students explain if mobility is a necessary criterion for categorizing
an organism as an animal.
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Ask students to explain the benefits and negative aspects of bilateral
symmetry.
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Analysis
Synthesis
Evaluation
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Have students describe the pros and cons of using anatomical features to
classify animals.
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Have students debate whether highly conserved DNA or highly variable
DNA is best for distinguishing differences between two species of
animals within the same genus.
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Ask students to explain the evidence supporting that metazoans were
derived from colonial protists.
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Ask students explain how hox gene mutations that produce limb variation
in animals can be used as a model for human birth defects.
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Have students find an agricultural application for a chemical that
regulates segmentation genes in animals.
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Ask the students to find a medical application that exploits indeterminate
development in deuterostome embryos.
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Ask students evaluate the benefits and risks of using research animals to
study human disease.
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Ask students to evaluate the accuracy of studying echinoderm embryos as
a way of better understanding human development.
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Ask students to evaluate the effectiveness and safety of any veterinary
treatment used to kill pathogenic worms that live in pets.
VISUAL RESOURCES
Have specimens on hand of all phyla—pictures are o.k., but actual specimens of corals,
anemones, hydra, sea stars, flatworms, roundworms, segmented worms, and various arthropods
are necessary for the student to see the diversity in form between all animals. Most students are
not familiar with the appearance of a real sponge, not even a spongin skeleton. They are only
familiar with the multicolored “Pseudospongia plastica.” Bring in examples and/or photographs
of others, especially finger sponges and freshwater Spongilla.
Recommend a trip to a nearby marine aquarium if possible.
IN-CLASS CONCEPTUAL DEMONSTRATIONS
A. A Remote Demonstration.
Introduction
Few students realize that researcher modern animal behavior studies are done using
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remote cameras that can measure animal movement, body temperature, and other physiological
parameters. This demonstration permits the class to see live video-cameras animal study in
which a series of cameras can be controlled by the instructor.
Materials
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Computer with Media Player and Internet access
LCD hooked up to computer
Web browser linked to Racerocks.com at http://142.31.86.230/Ex1/.
Procedure & Inquiry
1. Ask the class why it is preferable for researchers to study animals in nature and without
disturbing the animals.
2. Then explain you want to see a model experiment using videocams to study animal
behavior and habitats.
3. Load up the website and click on one of the videocams.
4. Then use the controls to scan the environment and the class to hypothesize the location of
the area and any obvious habitats.
5. Then ask the class to determine the animals being studied in the camera views. Also ask
them to think about any other animals that can be the subject of study by the cameras.
6. Start the first.
7. Ask the students briefly explain the types of information that can be gathered using the
videocams to record the animal.
8. Let the students know that the information is saved in video databases and assessed with
statistical that calculates various things going on with the animals.
USEFUL INTERNET RESOURCES
1. Images of animals are available from the University of California at Berkeley CalPhotos:
Animal website. These images are valuable teaching resources for lecture and laboratory
sessions. The site is available at http://calphotos.berkeley.edu/fauna/.
2. A fabulous book called The Naked Ape, written by Zoologist Desmond Morris, was the
first work of its kind that investigated humans from a zoologist’s perspective. A news
release about the impact of Morris’s work reminds student that humans are “just another
member of the Animal kingdom. The article is located at
http://news.bbc.co.uk/onthisday/hi/dates/stories/october/12/newsid_3116000/3116329.st
m.
3. The Tree of Life website provides up to date information about animal classification. It
has useful information and images for showing students diversity of animals. The website
can be found at http://tolweb.org/Animals/2374.
4. Case studies are an effective tool for stimulating interest in a lesson on fungi. The
University of Buffalo has a case study called “A Strange Fish Indeed: The “Discovery” of
a Living Fossil” which has students investigating new animal taxonomic discoveries. It
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uses the Coelocanth as a model organism for working out animal taxonomy. The case
study can be found at http://www.sciencecases.org/strange_fish/strange_fish.pdf.
LABORATORY IDEAS
A. Brine Shrimp as a Toxicology Model
This activity has students design an experiment in which use brine shrimp amoebocytes
(white blood cells) as a model of animal toxicology.
a. Explain to students how animals and animal cells are used in medicine and research as
models for human studies.
b. Tell students that they will be investigating the conditions needed for fungal spore
germination in two types of fungi.
c. Provide students with the following materials
a. Large brine shrimp in chilled water
b. Microscope
c. Microscope slides
d. Plastic pipette
e. 0.5% Trypan Blue solution in dropper bottle
f. Sharp scalpel
g. Standard Cytotoxic Solution of household bleach in a dropper
h. Test solutions with droppers
i. Endotoxins (agar or solution from Gram – bacterial colony)
ii. Pesticide
iii. 70% Ethanol
iv. Sterile water
v. Solutions students may request if available
d. Instruct students how to collect amoebocytes form the tail of a brine shrimp:
a. Place the cooled shrimp on a slide with minimum amount of water
b. Carefully slice off the tail at the base of the shrimps body
c. Quickly place the shrimp on the microscope and focus on the cut area under
medium to high power.
d. Add 2 drops of trypan blue.
e. Observe the amoebocytes which are small ovoid cells that leak out with the
blood.
f. Healthy amoebocytes are clear and show some cytoplasmic granules.
g. Dying and dead amoebocytes turn blue as they take up the trypan blue.
e. Have the students use the bleach as a cytotoxicity control to kill the amoebocytes. This is
done by adding on drop of bleach to the cells in the trypan blue while observing the
amoebocytes under the microcope. Have them notice how the dying and dead shrimp
cells and amoebocytes turn blue.
f. Then tell the students to test the other materials and make conclusions about their results.
LEARNING THROUGH SERVICE
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Service learning is a strategy of teaching, learning and reflective assessment that merges the
academic curriculum with meaningful community service. As a teaching methodology, it falls
under the category of experiential education. It is a way students can carry out volunteer projects
in the community for public agencies, nonprofit agencies, civic groups, charitable organizations,
and governmental organizations. It encourages critical thinking and reinforces many of the
concepts learned in a course.
1. Have students do a lesson do a hands-on program on the diversity of animals at a nature
center.
2. Have students tutor high school students animal diversity.
3. Have students volunteer on environmental restoration projects with a local conservation
group.
4. Have students volunteer at the educational center of a zoo or marine park.
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