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An Introduction to Animal Diversity

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1 An Introduction to Animal Diversity
Chapter 32 An Introduction to Animal Diversity

2 Overview: Welcome to Your Kingdom
The animal kingdom extends far beyond humans and other animals we may encounter 1.3 million living species of animals have been identified Video: Coral Reef

3 Fig. 32-1 Figure 32.1 Which of these organisms are animals?

4 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

5 Nutritional Mode Animals are heterotrophs that ingest their food

6 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 to animals

7 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 blastula The blastula undergoes gastrulation, forming a gastrula with different layers of embryonic tissues Video: Sea Urchin Embryonic Development

8 Cleavage Zygote Eight-cell stage Fig. 32-2-1
Figure 32.2 Early embryonic development in animals

9 Cross section of blastula
Fig Cleavage Cleavage Blastula Zygote Eight-cell stage Blastocoel Figure 32.2 Early embryonic development in animals Cross section of blastula

10 Cross section of blastula
Fig Blastocoel Endoderm Cleavage Cleavage Blastula Ectoderm Archenteron Zygote Eight-cell stage Gastrulation Gastrula Blastocoel Blastopore Figure 32.2 Early embryonic development in animals Cross section of blastula

11 Many animals have at least one larval stage
A larva is sexually immature and morphologically distinct from the adult; it eventually undergoes metamorphosis

12 All 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

13 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 875 million years ago This ancestor may have resembled modern choanoflagellates, protists that are the closest living relatives of animals

14 Individual choanoflagellate Choanoflagellates OTHER EUKARYOTES Sponges
Fig. 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

15 Neoproterozoic Era (1 Billion–524 Million Years Ago)
Early members of the animal fossil record include the Ediacaran biota, which dates from 565 to 550 million years ago

16 (a) Mawsonites spriggi (b) Spriggina floundersi
Fig. 32-4 1.5 cm 0.4 cm Figure 32.4 Ediacaran fossils (a) Mawsonites spriggi (b) Spriggina floundersi

17 (a) Mawsonites spriggi
Fig. 32-4a 1.5 cm Figure 32.4 Ediacaran fossils (a) Mawsonites spriggi

18 (b) Spriggina floundersi
Fig. 32-4b 0.4 cm Figure 32.4 Ediacaran fossils (b) Spriggina floundersi

19 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 New predator-prey relationships A rise in atmospheric oxygen The evolution of the Hox gene complex

20 Fig. 32-5 Figure 32.5 A Cambrian seascape

21 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

22 Mesozoic Era (251–65.5 Million Years Ago)
Coral reefs emerged, becoming important marine ecological niches for other organisms During the Mesozoic era, dinosaurs were the dominant terrestrial vertebrates The first mammals emerged

23 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 Modern mammal orders and insects diversified during the Cenozoic

24 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 A grade is a group whose members share key biological features A grade is not necessarily a clade, or monophyletic group

25 RESULTS Site of gastrulation Site of gastrulation 100 µm Fig. 32-6
Figure 32.6 Did β–catenin play an ancient role in the molecular control of gastrulation?

26 Fig. 32-6a RESULTS Figure 32.6 Did β–catenin play an ancient role in the molecular control of gastrulation? 100 µm

27 RESULTS Site of gastrulation Fig. 32-6b
Figure 32.6 Did β–catenin play an ancient role in the molecular control of gastrulation?

28 RESULTS Site of gastrulation Fig. 32-6c
Figure 32.6 Did β–catenin play an ancient role in the molecular control of gastrulation?

29 Fig. 32-6d RESULTS Figure 32.6 Did β–catenin play an ancient role in the molecular control of gastrulation?

30 Symmetry Animals can be categorized according to the symmetry of their bodies, or lack of it Some animals have radial symmetry

31 (b) Bilateral symmetry
Fig. 32-7 (a) Radial symmetry Figure 32.7 Body symmetry (b) Bilateral symmetry

32 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

33 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

34 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 Diploblastic animals have ectoderm and endoderm Triploblastic animals also have an intervening mesoderm layer; these include all bilaterians

35 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

36 Fig. 32-8 Coelom Body covering (from ectoderm) Tissue layer lining coelom and suspending internal organs (from mesoderm) Digestive tract (from endoderm) (a) Coelomate Body covering (from ectoderm) Pseudocoelom Muscle layer (from mesoderm) Digestive tract (from endoderm) (b) Pseudocoelomate Figure 32.8 Body cavities of triploblastic animals Body covering (from ectoderm) Tissue- filled region (from mesoderm) Wall of digestive cavity (from endoderm) (c) Acoelomate

37 Coelom Body covering (from ectoderm) Tissue layer lining coelom
Fig. 32-8a Coelom Body covering (from ectoderm) Tissue layer lining coelom and suspending internal organs (from mesoderm) Digestive tract (from endoderm) Figure 32.8a Body cavities of triploblastic animals (a) Coelomate

38 A pseudocoelom is a body cavity derived from the mesoderm and endoderm
Triploblastic animals that possess a pseudocoelom are called pseudocoelomates

39 Body covering (from ectoderm) Pseudocoelom Muscle layer (from
Fig. 32-8b Body covering (from ectoderm) Pseudocoelom Muscle layer (from mesoderm) Digestive tract (from endoderm) Figure 32.8b Body cavities of triploblastic animals (b) Pseudocoelomate

40 Triploblastic animals that lack a body cavity are called acoelomates

41 Wall of digestive cavity (from endoderm)
Fig. 32-8c Body covering (from ectoderm) Tissue- filled region (from mesoderm) Wall of digestive cavity (from endoderm) Figure 32.8c Body cavities of triploblastic animals (c) Acoelomate

42 Protostome and Deuterostome Development
Based on early development, many animals can be categorized as having protostome development or deuterostome development

43 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

44 Protostome development Deuterostome development (examples: echinoderm,
Fig. 32-9 Protostome development (examples: molluscs, annelids) Deuterostome development (examples: echinoderm, chordates) (a) Cleavage Eight-cell stage Eight-cell stage Spiral and determinate Radial and indeterminate Key (b) Coelom formation Coelom Ectoderm Mesoderm Archenteron Endoderm 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 Mouth Anus Mouth develops from blastopore. Anus develops from blastopore.

45 Protostome development (examples: molluscs, annelids)
Fig. 32-9a Protostome development (examples: molluscs, annelids) Deuterostome development (examples: echinoderms, chordates) (a) Cleavage Eight-cell stage Eight-cell stage Figure 32.9a A comparison of protostome and deuterostome development Spiral and determinate Radial and indeterminate

46 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

47 Protostome development (examples: molluscs, annelids)
Fig. 32-9b Protostome development (examples: molluscs, annelids) Deuterostome development (examples: echinoderms, chordates) (b) Coelom formation Coelom Key Ectoderm Archenteron Mesoderm Endoderm Coelom Mesoderm Figure 32.9b A comparison of protostome and deuterostome development Blastopore Blastopore Mesoderm Solid masses of mesoderm split and form coelom. Folds of archenteron form coelom.

48 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

49 Protostome development (examples: molluscs, annelids)
Fig. 32-9c Protostome development (examples: molluscs, annelids) Deuterostome development (examples: echinoderms, chordates) (c) Fate of the blastopore Anus Mouth Key Ectoderm Digestive tube Mesoderm Endoderm Figure 32.9c A comparison of protostome and deuterostome development Mouth Anus Mouth develops from blastopore. Anus develops from blastopore.

50 Concept 32.4: New views of animal phylogeny are emerging from molecular data
Zoologists recognize about three dozen animal phyla Current debate in animal systematics has led to the development of two phylogenetic hypotheses, but others exist as well

51 One hypothesis of animal phylogeny is based mainly on morphological and developmental comparisons

52 “Porifera” Cnidaria Metazoa ANCESTRAL COLONIAL FLAGELLATE Ctenophora
Fig “Porifera” Cnidaria ANCESTRAL COLONIAL FLAGELLATE Metazoa Ctenophora Eumetazoa Ectoprocta Brachiopoda Deuterostomia Echinodermata Chordata Bilateria Platyhelminthes Figure A view of animal phylogeny based mainly on morphological and developmental comparisons Rotifera Protostomia Mollusca Annelida Arthropoda Nematoda

53 One hypothesis of animal phylogeny is based mainly on molecular data

54 Silicea “Porifera” Metazoa Calcarea ANCESTRAL COLONIAL FLAGELLATE
Fig Silicea “Porifera” Calcarea ANCESTRAL COLONIAL FLAGELLATE Metazoa Ctenophora Cnidaria Eumetazoa Acoela Echinodermata Deuterostomia Chordata Bilateria Platyhelminthes Rotifera Ectoprocta Figure A view of animal phylogeny based mainly on molecular data Lophotrochozoa Brachiopoda Mollusca Annelida Nematoda Ecdysozoa Arthropoda

55 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

56 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

57 Fig Figure Ecdysis

58 Some lophotrochozoans have a feeding structure called a lophophore
Other phyla go through a distinct developmental stage called the trochophore larva

59 (b) Structure of a trochophore larva
Fig Lophophore Apical tuft of cilia Mouth Figure Morphological characteristics found among lophotrochozoans 100 µm Anus (a) An ectoproct (b) Structure of a trochophore larva

60 Future Directions in Animal Systematics
Phylogenetic studies based on larger databases will likely provide further insights into animal evolutionary history

61 Common ancestor of all animals Sponges (basal animals) Ctenophora
Fig. 32-UN1 Common ancestor of all animals Sponges (basal animals) Metazoa Ctenophora Eumetazoa Cnidaria True tissues Acoela (basal bilaterians) Deuterostomia Bilateria (most animals) Bilateral summetry Lophotrochozoa Three germ layers Ecdysozoa

62 Fig. 32-T1

63 Fig. 32-UN2

64 You should now be able to:
List the characteristics that combine to define animals Summarize key events of the Paleozoic, Mesozoic, and Cenozoic eras 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

65 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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