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CHAPTER 32

AN INTRODUCTION TO ANIMAL DIVERSITY

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I. Concept 32.1: What is an Animal?1. 95% are invertebrates2. Multicellular3. Eukaryotic4. Heterotrophic (ingestive)5. Lack cell walls6. Most are mobile7. Diploid with haploid gametes8. Sexual reproduction (zygote blastula gastrula)

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Embryology--Cleavage

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9. Carbohydrates stored as glycogen10. Some produce larva which undergo metamorphosis11. Specialized systems12. Two unique types of tissue: nervous tissue and muscle tissue 13. Share the unique homeobox-containing family of regulatory

genes know as Hox genesHox genes play an important role in development of animal

embryos

II. Concept 32.2: Animal HistoryA. Common Ancestor

Such a colony is about 0.02mm high.

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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.

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III. Concept 32.3: Body PlansA. Phylogeny

1. Define as the evolutionary history of species2. Based on general features of morphology and development3. 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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ANIMALSMetazoa

Parazoa Eumetazoa

Radiata Bilateria

Acoelomate Pseudocoelomate Coelomate

Deuterostomes Protostomes

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B. Major Branches of the Animal Kingdom1. Subkingdom Parazoa

Simple anatomy (lack true tissues) Phylum Porifera

2. Subkingdom Eumetazoa True tissues All other phyla

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C. Body PlansA body plan is a set of morphological and developmental traits

1.Symmetry•Animals can be categorized by body symmetry or the lack of ita. 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. Tissuesa. Tissues are collections of specialized cells isolated from other tissues by membranous layersb. 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. DiploblasticTissues develop from two germ layers (ectoderm or endoderm)

d. TriploblasticTissues 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 walla. 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 cavity1. Fluid cushions the suspended organs, helping to prevent

internal injury2. 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. Deuterostomia2 evolutionary lines in coelomatesDiffer in cleavage, fate of blastopore, and coelom formationProtostomes—mollusks, annelids, arthropodsDeuterostomes—echinoderms, chordates

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a. CleavageProtostomes•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 FormationProtostomes•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 BlastoporeBlastopore—first opening of archenteron (gut) which

forms from blastula during gastrulationProtostomes

--Blastopore becomes the mouthDeuterostomes

--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 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

1. All animals share a common ancestor2. Sponges are basal animals3. Eumetazoa is a clade of animals (eumetazoans) with true

tissues4. Most animals phyla belong to the clade Bilateria and are

called bilaterians5. Chordates and some other phyla belong to the clade

Deuterostomia

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B. Progress in resolving Bilaterian Relationships1. The morphology-based tree divides bilaterians into two clades:

deuterostomes and protostomes2. In contrast, recent molecular studies indicate three bilaterian

clades: Deuterostomia, Ecdysozoa, and Lophotrochozoaa. 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: Zygote Cleavages Blastula Gastrula Ectoderm Endoderm Mesoderm Blastopore Archenteron Metamorphosis

Radial symmetry Bilateral symmetry Cephalization Acoelomate Pseudocoelomate Coelomate Anterior Posterior Dorsal Ventral

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Ecdysis

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Trochophore Larva

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You should now be able to:1. List the characteristics that combine to define animals2. 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

3. Compare the developmental differences between protostomes and deuterostomes

4. Compare the alternate relationships of annelids and arthropods presented by two different proposed phylogenetic trees

5. Distinguish between ecdysozoans and lophotrochozoans