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An Overview of Animal Diversity
Chapter 32 An Overview of Animal Diversity
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Overview: Welcome to Your Kingdom
The animal kingdom extends far beyond humans and other animals we may encounter Scientists have identified 1.3 million living species of animals Animation: Coral Reef © 2011 Pearson Education, Inc.
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Figure 32.1 Figure 32.1 Which of these organisms are animals? 3
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Concept 32.1: Animal are multicellular, heterotrophic eukaryotes with tissues that develop from embryonic layers There are exceptions to nearly every criterion for distinguishing animals from other life-forms Several characteristics, taken together, sufficiently define the group © 2011 Pearson Education, Inc.
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Nutritional Mode Animals are heterotrophs that ingest their food
© 2011 Pearson Education, Inc.
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Cell Structure and Specialization
Animals are multicellular eukaryotes Their cells lack cell walls Their bodies are held together by structural proteins such as collagen Nervous tissue and muscle tissue are unique, defining characteristics of animals Tissues are groups of cells that have a common structure, function, or both © 2011 Pearson Education, Inc.
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Reproduction and Development
Most animals reproduce sexually, with the diploid stage usually dominating the life cycle After a sperm fertilizes an egg, the zygote undergoes rapid cell division called cleavage Cleavage leads to formation of a multicellular, hollow blastula The blastula undergoes gastrulation, forming a gastrula with different layers of embryonic tissues Video: Sea Urchin Embryonic Development © 2011 Pearson Education, Inc.
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Zygote Cleavage Eight-cell stage Figure 32.2-1
Figure 32.2 Early embryonic development in animals. 8
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Cross section of blastula
Figure Zygote Cleavage Blastocoel Cleavage Eight-cell stage Cross section of blastula Blastula Figure 32.2 Early embryonic development in animals. 9
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Cross section of blastula Cross section of gastrula
Figure Zygote Cleavage Blastocoel Cleavage Eight-cell stage Cross section of blastula Gastrulation Blastula Figure 32.2 Early embryonic development in animals. Blastocoel Endoderm Ectoderm Archenteron Cross section of gastrula Blastopore 10
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Many animals have at least one larval stage
A larva is sexually immature and morphologically distinct from the adult; it eventually undergoes metamorphosis A juvenile resembles an adult, but is not yet sexually mature © 2011 Pearson Education, Inc.
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Most animals, and only animals, have Hox genes that regulate the development of body form
Although the Hox family of genes has been highly conserved, it can produce a wide diversity of animal morphology © 2011 Pearson Education, Inc.
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Concept 32.2: The history of animals spans more than half a billion years
The animal kingdom includes a great diversity of living species and an even greater diversity of extinct ones The common ancestor of living animals may have lived between 675 and 800 million years ago This ancestor may have resembled modern choanoflagellates, protists that are the closest living relatives of animals © 2011 Pearson Education, Inc.
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Individual choanoflagellate
Figure 32.3 Individual choanoflagellate Choanoflagellates OTHER EUKARYOTES Sponges Figure 32.3 Three lines of evidence that choanoflagellates are closely related to animals. Animals Collar cell (choanocyte) Other animals 14
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Neoproterozoic Era (1 Billion–542 Million Years Ago)
Early members of the animal fossil record include the Ediacaran biota, which dates from 565 to 550 million years ago © 2011 Pearson Education, Inc.
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(a) Mawsonites spriggi (b) Spriggina floundersi
Figure 32.4 1.5 cm 0.4 cm Figure 32.4 Ediacaran fossils. (a) Mawsonites spriggi (b) Spriggina floundersi 16
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(a) Mawsonites spriggi
Figure 32.4a 1.5 cm Figure 32.4 Ediacaran fossils. (a) Mawsonites spriggi 17
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(b) Spriggina floundersi
Figure 32.4b 0.4 cm Figure 32.4 Ediacaran fossils. (b) Spriggina floundersi 18
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Paleozoic Era (542–251 Million Years Ago)
The Cambrian explosion (535 to 525 million years ago) marks the earliest fossil appearance of many major groups of living animals There are several hypotheses regarding the cause of the Cambrian explosion and decline of Ediacaran biota New predator-prey relationships A rise in atmospheric oxygen The evolution of the Hox gene complex © 2011 Pearson Education, Inc.
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Figure 32.5 Figure 32.5 A Cambrian seascape. 20
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Animals began to make an impact on land by 460 million years ago
Animal diversity continued to increase through the Paleozoic, but was punctuated by mass extinctions Animals began to make an impact on land by 460 million years ago Vertebrates made the transition to land around 360 million years ago © 2011 Pearson Education, Inc.
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Mesozoic Era (251–65.5 Million Years Ago)
Coral reefs emerged, becoming important marine ecological niches for other organisms The ancestors of plesiosaurs were reptiles that returned to the water During the Mesozoic era, dinosaurs were the dominant terrestrial vertebrates The first mammals emerged Flowering plants and insects diversified © 2011 Pearson Education, Inc.
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Cenozoic Era (65.5 Million Years Ago to the Present)
The beginning of the Cenozoic era followed mass extinctions of both terrestrial and marine animals These extinctions included the large, nonflying dinosaurs and the marine reptiles Mammals increased in size and exploited vacated ecological niches The global climate cooled © 2011 Pearson Education, Inc.
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Concept 32.3: Animals can be characterized by “body plans”
Zoologists sometimes categorize animals according to a body plan, a set of morphological and developmental traits Some developmental characteristics are conservative For example, the molecular control of gastrulation is conserved among diverse animal groups © 2011 Pearson Education, Inc.
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Early stages of development
Figure 32.6 RESULTS 1 Early stages of development 100 m 2 32-cell stage Site of gastrulation 3 Early gastrula stage Site of gastrulation Figure 32.6 Inquiry: Did -catenin play an ancient role in the molecular control of gastrulation? 4 Embryos with blocked -catenin activity 25
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Early stage of development
Figure 32.6a 100 m Early stage of development Figure 32.6 Inquiry: Did -catenin play an ancient role in the molecular control of gastrulation? 26
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Site of gastrulation 32-cell stage Figure 32.6b
Figure 32.6 Inquiry: Did -catenin play an ancient role in the molecular control of gastrulation? 27
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Site of gastrulation Early gastrula stage Figure 32.6c
Figure 32.6 Inquiry: Did -catenin play an ancient role in the molecular control of gastrulation? Early gastrula stage 28
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Embryos with blocked -catenin activity
Figure 32.6d Embryos with blocked -catenin activity Figure 32.6 Inquiry: Did -catenin play an ancient role in the molecular control of gastrulation? 29
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Symmetry Animals can be categorized according to the symmetry of their bodies, or lack of it Some animals have radial symmetry, with no front and back, or left and right © 2011 Pearson Education, Inc.
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(b) Bilateral symmetry
Figure 32.7 (a) Radial symmetry Figure 32.7 Body symmetry. (b) Bilateral symmetry 31
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Two-sided symmetry is called bilateral symmetry
Bilaterally symmetrical animals have A dorsal (top) side and a ventral (bottom) side A right and left side Anterior (head) and posterior (tail) ends Cephalization, the development of a head © 2011 Pearson Education, Inc.
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Radial animals are often sessile or planktonic (drifting or weakly swimming)
Bilateral animals often move actively and have a central nervous system © 2011 Pearson Education, Inc.
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Tissues Animal body plans also vary according to the organization of the animal’s tissues Tissues are collections of specialized cells isolated from other tissues by membranous layers During development, three germ layers give rise to the tissues and organs of the animal embryo © 2011 Pearson Education, Inc.
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Ectoderm is the germ layer covering the embryo’s surface
Endoderm is the innermost germ layer and lines the developing digestive tube, called the archenteron © 2011 Pearson Education, Inc.
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Sponges and a few other groups lack true tissues
Diploblastic animals have ectoderm and endoderm These include cnidarians and comb jellies Triploblastic animals also have an intervening mesoderm layer; these include all bilaterians These include flatworms, arthropods, vertebrates, and others © 2011 Pearson Education, Inc.
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Body Cavities Most triploblastic animals possess a body cavity
A true body cavity is called a coelom and is derived from mesoderm Coelomates are animals that possess a true coelom © 2011 Pearson Education, Inc.
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Body covering (from ectoderm)
Figure 32.8 (a) Coelomate Coelom Body covering (from ectoderm) Tissue layer lining coelom and suspending internal organs (from mesoderm) Digestive tract (from endoderm) (b) Pseudocoelomate Body covering (from ectoderm) Pseudocoelom Muscle layer (from mesoderm) Digestive tract (from endoderm) Figure 32.8 Body cavities of triploblastic animals. (c) Acoelomate Body covering (from ectoderm) Tissue- filled region (from mesoderm) Wall of digestive cavity (from endoderm) 38
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Body covering (from ectoderm)
Figure 32.8a (a) Coelomate Coelom Body covering (from ectoderm) Tissue layer lining coelom and suspending internal organs (from mesoderm) Digestive tract (from endoderm) Figure 32.8 Body cavities of triploblastic animals. 39
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A pseudocoelom is a body cavity derived from the mesoderm and endoderm
Triploblastic animals that possess a pseudocoelom are called pseudocoelomates © 2011 Pearson Education, Inc.
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Body covering (from ectoderm)
Figure 32.8b (b) Pseudocoelomate Body covering (from ectoderm) Pseudocoelom Muscle layer (from mesoderm) Digestive tract (from endoderm) Figure 32.8 Body cavities of triploblastic animals. 41
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Triploblastic animals that lack a body cavity are called acoelomates
© 2011 Pearson Education, Inc.
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Body covering (from ectoderm) Tissue- filled region (from mesoderm)
Figure 32.8c (c) Acoelomate Body covering (from ectoderm) Tissue- filled region (from mesoderm) Wall of digestive cavity (from endoderm) Figure 32.8 Body cavities of triploblastic animals. 43
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Coelomates and pseudocoelomates belong to the same grade
A grade is a group whose members share key biological features A grade is not necessarily a clade, an ancestor and all of its descendents © 2011 Pearson Education, Inc.
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Protostome and Deuterostome Development
Based on early development, many animals can be categorized as having protostome development or deuterostome development © 2011 Pearson Education, Inc.
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Cleavage In protostome development, cleavage is spiral and determinate
In deuterostome development, cleavage is radial and indeterminate With indeterminate cleavage, each cell in the early stages of cleavage retains the capacity to develop into a complete embryo Indeterminate cleavage makes possible identical twins, and embryonic stem cells © 2011 Pearson Education, Inc.
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Protostome development (examples: molluscs, annelids)
Fig ure 32.9 Protostome development (examples: molluscs, annelids) Deuterostome development (examples: echinoderms, chordates) (a) Cleavage Eight-cell stage Eight-cell stage Spiral and determinate Radial and indeterminate (b) Coelom formation Coelom Archenteron Coelom Mesoderm Blastopore Blastopore Mesoderm Solid masses of mesoderm split and form coelom. Folds of archenteron form coelom. Figure 32.9 A comparison of protostome and deuterostome development. (c) Fate of the blastopore Anus Mouth Digestive tube Key Ectoderm Mouth Anus Mesoderm Mouth develops from blastopore. Anus develops from blastopore. Endoderm 47
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Protostome development (examples: molluscs, annelids)
Figure 32.9a (a) Cleavage Protostome development (examples: molluscs, annelids) Deuterostome development (examples: echinoderms, chordates) Eight-cell stage Eight-cell stage Key Ectoderm Mesoderm Figure 32.9 A comparison of protostome and deuterostome development. Spiral and determinate Radial and indeterminate Endoderm 48
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Coelom Formation In protostome development, the splitting of solid masses of mesoderm forms the coelom In deuterostome development, the mesoderm buds from the wall of the archenteron to form the coelom © 2011 Pearson Education, Inc.
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Protostome development (examples: molluscs, annelids)
Figure 32.9b (b) Coelom formation Protostome development (examples: molluscs, annelids) Deuterostome development (examples: echinoderms, chordates) Coelom Archenteron Coelom Key Figure 32.9 A comparison of protostome and deuterostome development. Mesoderm Blastopore Blastopore Mesoderm Ectoderm Solid masses of mesoderm split and form coelom. Folds of archenteron form coelom. Mesoderm Endoderm 50
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Fate of the Blastopore The blastopore forms during gastrulation and connects the archenteron to the exterior of the gastrula In protostome development, the blastopore becomes the mouth In deuterostome development, the blastopore becomes the anus © 2011 Pearson Education, Inc.
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Protostome development (examples: molluscs, annelids)
Figure 32.9c (c) Fate of the blastopore Protostome development (examples: molluscs, annelids) Deuterostome development (examples: echinoderms, chordates) Anus Mouth Digestive tube Key Ectoderm Figure 32.9 A comparison of protostome and deuterostome development. Mouth Anus Mesoderm Mouth develops from blastopore. Anus develops from blastopore. Endoderm 52
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Concept 32.4: New views of animal phylogeny are emerging from molecular data
Zoologists recognize about three dozen animal phyla Phylogenies now combine morphological, molecular, and fossil data Current debate in animal systematics has led to the development of multiple hypotheses about the relationships among animal groups © 2011 Pearson Education, Inc.
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One hypothesis of animal phylogeny is based mainly on morphological and developmental comparisons
© 2011 Pearson Education, Inc.
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ANCESTRAL COLONIAL FLAGELLATE Metazoa
Figure 32.10 Porifera Cnidaria ANCESTRAL COLONIAL FLAGELLATE Metazoa Ctenophora Eumetazoa Ectoprocta Brachiopoda Deuterostomia Echinodermata Chordata Bilateria Platyhelminthes Rotifera Figure A view of animal phylogeny based mainly on morphological and developmental comparisons. Protostomia Mollusca Annelida Arthropoda Nematoda 55
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One hypothesis of animal phylogeny is based mainly on molecular data
© 2011 Pearson Education, Inc.
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ANCESTRAL COLONIAL FLAGELLATE Ctenophora Metazoa
Figure 32.11 Porifera ANCESTRAL COLONIAL FLAGELLATE Ctenophora Metazoa Cnidaria Eumetazoa Acoela Echinodermata Chordata Deuterostomia Bilateria Platyhelminthes Rotifera Ectoprocta Lophotrochozoa Figure A view of animal phylogeny based mainly on molecular data. Brachiopoda Mollusca Annelida Nematoda Ecdysozoa Arthropoda 57
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Points of Agreement All animals share a common ancestor
Sponges are basal animals Eumetazoa is a clade of animals (eumetazoans) with true tissues Most animal phyla belong to the clade Bilateria, and are called bilaterians Chordates and some other phyla belong to the clade Deuterostomia © 2011 Pearson Education, Inc.
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Progress in Resolving Bilaterian Relationships
The morphology-based tree divides bilaterians into two clades: deuterostomes and protostomes In contrast, recent molecular studies indicate three bilaterian clades: Deuterostomia, Ecdysozoa, and Lophotrochozoa Ecdysozoans shed their exoskeletons through a process called ecdysis © 2011 Pearson Education, Inc.
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Figure 32.12 Figure Ecdysis. 60
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Some lophotrochozoans have a feeding structure called a lophophore
Others go through a distinct developmental stage called the trochophore larva © 2011 Pearson Education, Inc.
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Lophophore feeding structures of an ectoproct (b)
Figure 32.13 Apical tuft of cilia Lophophore Mouth Figure Morphological characteristics of lophotrochozoans. Anus (a) Lophophore feeding structures of an ectoproct (b) Structure of a trochophore larva 62
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Lophophore feeding structures of an ectoproct
Figure 32.13a Lophophore Figure Morphological characteristics of lophotrochozoans. (a) Lophophore feeding structures of an ectoproct 63
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Future Directions in Animal Systematics
Phylogenetic studies based on larger databases will likely provide further insights into animal evolutionary history © 2011 Pearson Education, Inc.
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Figure 32.UN01 Figure 32.UN01 In-text figure, p. 656 65
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535–525 mya: Cambrian explosion
Figure 32.UN02 535–525 mya: Cambrian explosion Origin and diversification of dinosaurs 365 mya: Early land animals 565 mya: Ediacaran biota Diversification of mammals Era Ceno- zoic Neoproterozoic Paleozoic Mesozoic 1,000 542 Figure 32.UN02 Summary figure, Concept 32.2 251 65.5 Millions of years ago (mya) 66
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Common ancestor of all animals
Figure 32.UN03 Common ancestor of all animals Porifera (basal animals) Metazoa Ctenophora Eumetazoa Cnidaria True tissues Acoela (basal bilaterians) Figure 32.UN03 Summary figure, Concept 32.4 Deuterostomia Bilateria (most animals) Bilateral symmetry Lophotrochozoa Three germ layers Ecdysozoa 67
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Figure 32.UN04 Figure 32.UN04 Test Your Understanding, question 7 68
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Figure 32.UN05 Figure 32.UN05 Appendix A: Answer for Test Your Understanding, question 7 69
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