32
An Chapter Introduction to Animal Diversity
PowerPoint Lectures for Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
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Overview: Welcome to Your Kingdom The animal kingdom
Extends far beyond humans and other animals we may encounter
Figure 32.1
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Concept 32.1: Animal are multicellular, heterotrophic eukaryotes with tissues that develop from embryonic layers Several characteristics of animals
Sufficiently define the group
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Nutritional Mode Animals are heterotrophs
That ingest their food
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Cell Structure and Specialization Animals are multicellular eukaryotes Their cells lack cell walls
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Their bodies are held together
By structural proteins such as collagen
Nervous tissue and muscle tissue
Are unique to animals
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Reproduction and Development Most animals reproduce sexually
With the diploid stage usually dominating the life cycle
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After a sperm fertilizes an egg
The zygote undergoes cleavage, leading to the formation of a blastula
The blastula undergoes gastrulation
Resulting in the formation of embryonic tissue layers and a gastrula
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Early embryonic development in animals
1 The zygote of an animal undergoes a succession of mitotic cell divisions called cleavage. 2 Only one cleavage stagethe eight-cell embryois shown here. 3 In most animals, cleavage results in the formation of a multicellular stage called a blastula. The blastula of many animals is a hollow ball of cells.
Blastocoel
Cleavage
6 The endoderm of the archenteron develops into the tissue lining the animal's digestive tract.
Cleavage
Zygote
Eight-cell stage Blastocoel Endoderm
Blastula
Cross section of blastula
5 The blind pouch formed by gastrulation, called the archenteron, opens to the outside via the blastopore.
Ectoderm Gastrula
Blastopore
Gastrulation
4 Most animals also undergo gastrulation, a rearrangement of the embryo in which one end of the embryo folds inward, expands, and eventually fills the blastocoel, producing layers of embryonic tissues: the ectoderm (outer layer) and the endoderm (inner layer).
Figure 32.2
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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
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Concept 32.2: The history of animals may span more than a billion years The animal kingdom includes not only great diversity of living species
But the even greater diversity of extinct ones as well
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The common ancestor of living animals
May have lived 1.2 billion800 million years ago May have resembled modern choanoflagellates, protists that are the closest living relatives of animals
Single cell Stalk
Figure 32.3
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Was probably itself a colonial, flagellated protist
Somatic cells Digestive cavity
Reproductive cells Colonial protist, an aggregate of identical cells Hollow sphere of unspecialized cells (shown in cross section)
Beginning of cell specialization
Infolding
Gastrula-like "protoanimal"
Figure 32.4
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Neoproterozoic Era (1 Billion524 Million Years Ago)
Early members of the animal fossil record
Include the Ediacaran fauna
Figure 32.5a, b
(a)
(b)
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Paleozoic Era (542251 Million Years Ago) The Cambrian explosion
Marks the earliest fossil appearance of many major groups of living animals Is described by several current hypotheses
Figure 32.6
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Mesozoic Era (25165.5 Million Years Ago) During the Mesozoic era
Dinosaurs were the dominant terrestrial vertebrates Coral reefs emerged, becoming important marine ecological niches for other organisms
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Cenozoic Era (65.5 Million Years Ago to the Present)
The beginning of this era
Followed mass extinctions of both terrestrial and marine animals
Modern mammal orders and insects
Diversified during the Cenozoic
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Concept 32.3: Animals can be characterized by "body plans" One way in which zoologists categorize the diversity of animals
Is according to general features of morphology and development
A group of animal species
That share the same level of organizational complexity is known as a grade
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The set of morphological and developmental traits that define a grade
Are generally integrated into a functional whole referred to as a body plan
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Symmetry Animals can be categorized
According to the symmetry of their bodies, or lack of it
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Some animals have radial symmetry
Like in a flower pot
(a) Radial symmetry. The parts of a radial animal, such as a sea anemone (phylum Cnidaria), radiate from the center. Any imaginary slice through the central axis divides the animal into mirror images.
Figure 32.7a
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Some animals exhibit bilateral symmetry
Or two-sided symmetry
(b) Bilateral symmetry. A bilateral animal, such as a lobster (phylum Arthropoda), has a left side and a right side. Only one imaginary cut divides the animal into mirror-image halves.
Figure 32.7b
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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
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Tissues body Animal 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
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Animal embryos
Form germ layers, embryonic tissues, including ectoderm, endoderm, and mesoderm
Diploblastic animals
Have two germ layers
Triploblastic animals
Have three germ layers
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Body Cavities In triploblastic animals
A body cavity may be present or absent
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A true body cavity
Is called a coelom and is derived from mesoderm
Body covering (from ectoderm)
Coelom
(a) Coelomate. Coelomates such as annelids have a true coelom, a body cavity completely lined by tissue derived from mesoderm.
Tissue layer lining coelom and suspending internal organs (from mesoderm) Digestive tract (from endoderm)
Figure 32.8a
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A pseudocoelom
Is a body cavity derived from the blastocoel, rather than from mesoderm
Body covering (from ectoderm)
(b) Pseudocoelomate. Pseudocoelomates such as nematodes have a body cavity only partially lined by tissue derived from mesoderm.
Pseudocoelom
Muscle layer (from mesoderm)
Digestive tract (from ectoderm)
Figure 32.8b
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Organisms without body cavities
Are considered acoelomates
Body covering (from ectoderm) (c) Acoelomate. Acoelomates such as flatworms lack a body cavity between the digestive tract and outer body wall.
Tissuefilled region (from mesoderm)
Digestive tract (from endoderm)
Figure 32.8c
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Protostome and Deuterostome Development Based on certain features seen in early development
Many animals can be categorized as having one of two developmental modes: protostome development or deuterostome development
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Cleavage In protostome development
Cleavage is spiral and determinate
In deuterostome development
Cleavage is radial and indeterminate
Protostome development (examples: molluscs, annelids, arthropods) Eight-cell stage Deuterostome development (examples: echinoderms, chordates) Eight-cell stage (a) Cleavage. In general, protostome development begins with spiral, determinate cleavage. Deuterostome development is characterized by radial, indeterminate cleavage.
Spiral and determinate
Radial and indeterminate
Figure 32.9a
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Coelom Formation
In protostome development
The splitting of the initially solid masses of mesoderm to form the coelomic cavity is called schizocoelous development
In deuterostome development
Formation of the body cavity is described as Coelom (b) Coelom formation. Coelom enterocoelous development formation begins in the gastrula
Archenteron Coelom Mesoderm Blastopore Mesoderm Blastopore Enterocoelous: Schizocoelous: solid folds of archenteron masses of mesoderm form coelom split and form coelom stage. In protostome development, the coelom forms from splits in the mesoderm (schizocoelous development). In deuterostome development, the coelom forms from mesodermal outpocketings of the archenteron (enterocoelous development).
Figure 32.9b
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Fate of the Blastopore In protostome development
The blastopore becomes the mouth
In deuterostome development
The blastopore becomes the anus
Anus Mouth
Digestive tube
Mouth
Anus Anus develops from blastopore
Figure 32.9c
Mouth develops from blastopore
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Concept 32.4: Leading hypotheses agree on major features of the animal phylogenetic tree Zoologists currently recognize about 35 animal phyla The current debate in animal systematics
Has led to the development of two phylogenetic hypotheses, but others exist as well
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One hypothesis of animal phylogeny based mainly on morphological and developmental comparisons
Ctenophora Arthropoda Phoronida Platyhelminthes Cnidaria Echinodermata Chordata Mollusca Ectoprocta Brachiopoda Annelida Rotifera Nematoda Nemertea Porifera
"Radiata"
Deuterostomia
Protostomia
Bilateria
Eumetazoa
Metazoa Ancestral colonial flagellate
Figure 32.10
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One hypothesis of animal phylogeny based mainly on molecular data
Echinodermata Brachiopoda Platyhelminthes Ctenophora Chordata Cnidaria Phoronida Arthropoda Ectoprocta Nemertea Mollusca Silicarea Annelida Nematoda Calcarea Rotifera
"Radiata"
"Porifera"
Deuterostomia
Lophotrochozoa
Ecdysozoa
Bilateria
Eumetazoa
Metazoa
Figure 32.11
Ancestral colonial flagellate
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Points of Agreement All animals share a common ancestor Sponges are basal animals Eumetazoa is a clade of animals with true tissues
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Most animal phyla belong to the clade Bilateria Vertebrates and some other phyla belong to the clade Deuterostomia
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Disagreement over the Bilaterians The morphology-based tree
Divides the bilaterians into two clades: deuterostomes and protostomes
In contrast, several recent molecular studies
Generally assign two sister taxa to the protostomes rather than one: the ecdysozoans and the lophotrochozoans
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Ecdysozoans share a common characteristic
They shed their exoskeletons through a process called ecdysis
Figure 32.12
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Lophotrochozoans share a common characteristic
Called the lophophore, a feeding structure
Other phyla
Go through a distinct larval stage called a Apical tuft of cilia trochophore larva
Mouth
Figure 32.13a, b
(a) An ectoproct, a lophophorate
Anus (b) Structure of trochophore larva
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Future Directions in Animal Systematics Phylogenetic studies based on larger databases
Will likely provide further insights into animal evolutionary history
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