I. Concept 32.1: What is an Animal?

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CHAPTER 32
AN INTRODUCTION TO
ANIMAL DIVERSITY
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I. Concept 32.1: What is an Animal?
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95% are invertebrates
Multicellular
Eukaryotic
Heterotrophic (ingestive)
Lack cell walls
Most are mobile
Diploid with haploid gametes
Sexual reproduction (zygote  blastula  gastrula)
Embryology--Cleavage
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9. Carbohydrates stored as glycogen
10. Some produce larva which undergo metamorphosis
11. Specialized systems
12. Two unique types of tissue: nervous tissue and muscle tissue
13. Share the unique homeobox-containing family of regulatory
genes know as Hox genes
 Hox genes play an important role in development of animal
embryos
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II. Concept 32.2: Animal History
A. Common Ancestor
1. May have resembled modern
choanoflagellates
2. Choanoflagellates are protists that
are the closest living relatives of
animals and were probably a
colonial, flagellated protist.
Such a colony is about 0.02mm high.
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III. Concept 32.3: Body Plans
A. Phylogeny
1. Define as the evolutionary history of species
2. Based on general features of morphology and development
3. Each major branch represents a grade, (group of animal
species that share the same level of organizational
complexity)
4. A grade is not necessarily a clade or monophyletic group.
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ANIMALS
Parazoa
Radiata
Acoelomate
Metazoa
Eumetazoa
Bilateria
Pseudocoelomate
Deuterostomes
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Coelomate
Protostomes
B. Major Branches of the Animal Kingdom
1. Subkingdom Parazoa
 Simple anatomy (lack true tissues)
 Phylum Porifera
2. Subkingdom Eumetazoa
 True tissues
 All other phyla
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C. Body Plans
A body plan is a set of morphological and developmental traits
1.Symmetry
•Animals can be categorized by body symmetry or the lack of
it
a. Radial symmetry (Radiata)
-Characterized by a body shaped like a pie or barrel, with
many equal parts radiating outward like spokes of a wheel
-have oral and aboral sides but no front, back, left, or right
surfaces
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b. Bilateral symmetry (Bilateria)
-Characterized by a body form with a central longitudinal
plane dividing the body into two equal but opposite halves
-A dorsal (top) and ventral (bottom) sides
-Anterior (head) and posterior (tail) ends
-Left and right sides
-Exhibit cephalization (concentration of nerves and sense
organs on anterior end)
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SYMMETRY
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2. Tissues
a. Tissues are collections of specialized cells isolated from
other tissues by membranous layers
b. During gastrulation (downward and inward movement of cells
of blastula), three germ layers form which give rise to the
tissues and organs of the animal embryo
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c. Diploblastic
Tissues develop from two germ layers (ectoderm or
endoderm)
d. Triploblastic
Tissues develop from three germ layers:
1) Ectoderm is the outer most germ layer which develops
into outer layer and central nervous system
2) Endoderm is the inner most germ layer and lines the
developing digestive tube called the archenteron
3) Mesoderm is the middle layer which is located between
ectoderm and endoderm
Includes all bilaterians
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Germ Layers
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3. Body Cavity (Coelom)
 Defined as a fluid- or air-filled space separating the
digestive tract from the outer body wall
a. Acoelomate
• No body cavity between digestive tract and outer body
wall
• Area filled with cells
• Phylum Platyhelminthes
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Acoelomate
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b. Pseudocoelomate
• Body cavity lined with mesoderm and endoderm
• Tube within a tube
• Phyla: Nematoda
Rotifera
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Pseudocoelomate
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c. Coelomate (true body cavity)
• Body cavity lined with mesoderm
• Mesenteries connect outer and inner mesoderm and
suspend internal organs
• Phyla: Echinodermata
Arthropoda
Mollusca
Chordata
Annelida
 Functions of the body cavity
1. Fluid cushions the suspended organs, helping to prevent
internal injury
2. In soft-bodied coelomates, functions as a hydrostatic
skeleton against which muscles can work
3. Enables internal organs to grow and move independently
of the other body wall
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Coelomate
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4. Development--Protostomia vs. Deuterostomia
2 evolutionary lines in coelomates
Differ in cleavage, fate of blastopore, and coelom formation
Protostomes—mollusks, annelids, arthropods
Deuterostomes—echinoderms, chordates
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a. Cleavage
Protostomes
• Spiral Cleavage—cleavage diagonal to the embryo’s
vertical axis
Deuterostomes
• Radial Cleavage—cleavage either parallel or
perpendicular to embryo’s vertical axis
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b. Determination
 Protostomes
• Determinate Cleavage—developmental fate of each
cell determined very early
-A cell from 4-cell stage will not develop fully
 Deuterostomes
• Indeterminate Cleavage—early cells retain ability to
develop into complete embryo if isolated from other
cells
-Makes possible identical twins and embryonic
stem cells
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Cleavage
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c. Coelom Formation
Protostomes
•Schizocoelous—the splitting of solid masses of
mesoderm forms the coelom
Deuterostomes
• Enterocoelous—the mesoderm buds from the wall of
the archenteron to form the coelom
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Coelom Formation
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d. Fate of Blastopore
 Blastopore—first opening of archenteron (gut) which
forms from blastula during gastrulation
Protostomes
--Blastopore becomes the mouth
Deuterostomes
--Blastopore becomes the anus
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Fate of the Blastopore
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IV. Concept 32.4: New Views of
Animal Phylogeny
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One hypothesis of animal phylogeny is based mainly on
morphological and developmental comparisons
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Morphological Characteristics
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One hypothesis of animal phylogeny is based mainly on
molecular data
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Molecular Studies
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A. Points of Agreement
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All animals share a common ancestor
Sponges are basal animals
Eumetazoa is a clade of animals (eumetazoans) with true
tissues
Most animals phyla belong to the clade Bilateria and are
called bilaterians
Chordates and some other phyla belong to the clade
Deuterostomia
B. Progress in resolving Bilaterian Relationships
1. The morphology-based tree divides bilaterians into two clades:
deuterostomes and protostomes
2. In contrast, recent molecular studies indicate three bilaterian
clades: Deuterostomia, Ecdysozoa, and Lophotrochozoa
a. Ecdysozoans shed their exoskeletons through a process
called ecdysis (Arthropoda and Nematoda)
b. Some lophotrochozoans have a feeding structure called a
lophophore ( Mollusca, Annelida, Rotifera, Platyhelminthes)
c. Other phyla go through a distinct developmental stage
called the trochophore larva(Mollusca and Annelida)
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TERMS:
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Zygote
Cleavages
Blastula
Gastrula
Ectoderm
Endoderm
Mesoderm
Blastopore
Archenteron
Metamorphosis
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Radial symmetry
Bilateral symmetry
Cephalization
Acoelomate
Pseudocoelomate
Coelomate
Anterior
Posterior
Dorsal
Ventral
Ecdysis
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Trochophore Larva
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You should now be able to:
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List the characteristics that combine to define animals
Distinguish between the following pairs or sets of terms:
radial and bilateral symmetry; grade and clade of animal
taxa; diploblastic and triploblastic; spiral and radial
cleavage; determinate and indeterminate cleavage;
acoelomate, pseudocoelomate, and coelomate grades
Compare the developmental differences between
protostomes and deuterostomes
Compare the alternate relationships of annelids and
arthropods presented by two different proposed
phylogenetic trees
Distinguish between ecdysozoans and lophotrochozoans

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