Chapter 32
An Introduction to Animal Diversity
K. Animalia: Metazoa • Overview: Welcome to Your Kingdom • The animal kingdom is the most diverse group of living organisms: 1.3 million named species
PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece
Lectures by Chris Romero Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 32.1 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
General Features of the Animalia
Cell Structure and Specialization
• Animals are multicellular, heterotrophic eukaryotes with tissues that develop from embryonic layers
• Animals are multicellular, diploid eukaryotes:
• Several characteristics of animals – Sufficiently define the group
Multicellularity = Synapomorphy of Animalia • Animals undergo a unique Embryonic Development: Blastula, and later Gastrula (Eumetazoans) • Hox Genes: special pattern-formation genes • Their bodies are held together by structural proteins
such as collagen (synapomorphy?) • Cells lack cell walls (plesiomorphy) • Nervous tissue and muscle tissue are unique to Bilaterian animals = Synapomorphy of Bilateria Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Nutritional Mode
Reproduction and Development
• Animals are heterotrophs (plesiomorphy)
• Most animals reproduce sexually
– The Eumetazoa ingest their food in a Gut: Synapomorphy
– With the diploid stage dominating the life cycle (multicellular stage = diploid)
• After a sperm fertilizes an egg – The zygote undergoes cleavage, leading to the formation of a blastula: a multicellular embryo
• Eumetazoa Synapomorphy: – The blastula undergoes gastrulation: creating embryonic tissue layers & a gastrula with a gut Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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Animalia: Synapomorphy • Early embryonic development in animals 1 The zygote of an animal undergoes a succession of mitotic cell divisions called cleavage.
2 Only one cleavage stage–the eight-cell embryo–is shown here.
• All animals, and only animals have
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
Cleavage 6 The endoderm of the archenteron develops into the tissue lining the animal’s digestive tract.
Eight-cell stage
Zygote
Blastula
• Although the Hox family of genes has been highly conserved
Cross section of blastula
Blastocoel
– It can produce a wide diversity of animal morphology
Endoderm 5 The blind pouch formed by gastrulation, called the archenteron, opens to the outside via the blastopore.
– Hox genes that regulate the development of body form (homeotic genes)
Ectoderm Gastrula
Gastrulation
Blastopore
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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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Fig. 28-23
Origins and History of the Animalia
RESULTS
• The history of animals may span more than a billion years
Choanoflagellates Animals Unikonta Fungi
Common ancestor of all eukaryotes
• The great diversity of the Animal kingdom includes both living species and an even greater diversity of extinct species
Amoebozoans Diplomonads Excavata Euglenozoans Alveolates Chromalveolata Stramenopiles DHFR-TS gene fusion
Rhizarians
Rhizaria
Red algae Green algae
Archaeplastida
Plants Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Super Group Unikonta • The common ancestor of living animals
Synapomorphy: Single flagellum (ancestrally)
Gymnamoebas Entamoebas
Opisthokonts
Nucleariids Fungi
Unikonta
Amoebozoans
– May have lived 1.2 billion–800 million years ago Slime molds
– May have resembled modern choanoflagellates, protists that are the closest living relatives of animals
Choanoflagellates Animals Single cell Stalk
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Sister Groups: Animalia & Choanoflagellates • Shared cell structure of sponge choanocyte, also found in other animals
• The common ancestor of living animals – was probably a colonial, flagellated protist
• DNA similarities
Digestive cavity
Somatic cells
Individual choanoflagellate Choanoflagellates
OTHER EUKARYOTES
Reproductive cells
Sponges Animals
Colonial protist, an aggregate of identical cells
Hollow sphere of unspecialized cells (shown in cross section)
Beginning of cell specialization
Infolding
Gastrula-like “protoanimal”
Collar cell (choanocyte)
Figure 32.4
Other animals
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Neoproterozoic Era (1 Billion–524 Million Years Ago)
Paleozoic Era: Age of Fish (542–251 MYA)
• Early members of the animal fossil record
• The Cambrian explosion – Marks the earliest fossil appearance of many major groups of living animals
– Include the Ediacaran fauna
– Permian extinction ends the Paleozoic
Figure 32.5a, b
(a)
(b)
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Paleozoic Era: Age of Fish (542–251 MYA) This is a computer generated image issued by the University of Bristol in England released on Tuesday Nov. 20, 2007 showing a size comparison between a human an ancient sea scorpion. A fossil found in Germany indicates the ancient sea scorpion was once 2.5 metres (8 feet) long, making it the biggest bug ever known to have existed. This is a computer generated image issued by the University of Bristol in England released on Tuesday Nov. 20, 2007 showing a size comparison between a human an ancient sea scorpion. A fossil found in Germany indicates the ancient sea scorpion was once 2.5 metres (8 feet) long, making it the biggest bug ever known to have existed. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 32.6 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Mesozoic Era: Age of Reptiles (251–65.5 MYA) • During the Mesozoic era – Dinosaurs were the dominant terrestrial vertebrates – Coral reefs emerged, becoming important marine ecological niches for other organisms – Mass extinction (Meteor, Cretaceous period) ends the Mesozoic
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Cenozoic Era: Age of Mammals (65.5 MYA to Present)
Animal Classification: Body Plan vs. Molecules
• The beginning of this era
• Groups of the Animalia have been characterized by ‘body plans’
– Followed mass extinctions of both terrestrial and marine animals
• Modern mammal orders and insects – Diversified during the Cenozoic
• 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Symmetry
Radial Symmetry
• Animals can be categorized
• Some animals have radial symmetry
– According to the symmetry of their bodies, or lack of it
– Like in a flower pot
– Assymetrical organisms lack symmetry, e.g. some sponges
(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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Bilateral Symmetry • Some animals exhibit bilateral symmetry – Or two-sided symmetry
• Bilaterally symmetrical animals have – A dorsal (top) side and a ventral (bottom) side – A right and left side
(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.
– Anterior (head) and posterior (tail) ends – Cephalization, the development of a head
Figure 32.7b Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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Tissues
Tissues
• Animal body plans
• Animal embryos
– Also vary according to the organization of the animal’s tissues
• Tissues
– Form germ layers, embryonic tissues
• Diploblastic animals have two germ layers: • endoderm & ectoderm
– Are collections of specialized cells isolated from other tissues by membranous layers
• Triploblastic animals have three germ layers: • endoderm, ectoderm & mesoderm
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Body Cavities • In triploblastic animals a body cavity may be present: – Coelomate
Coelom
Digestive tract (from endoderm)
Body covering (from ectoderm) Tissue layer lining coelom and suspending internal organs (from mesoderm)
(a) Coelomate Body covering (from ectoderm) Pseudocoelom
– Pseudocoelomate
Coelomates have a ‘true’ body cavity • A true body cavity is called a coelom – derived from mesoderm
• Coeloms provide a hydrostatic skeleton and space for organs
Muscle layer (from mesoderm)
Body covering (from ectoderm)
Coelom
Digestive tract (from endoderm) (b) Pseudocoelomate
• Or, Absent
Body covering (from ectoderm)
– Acoelomate
Tissuefilled region (from mesoderm)
(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)
Wall of digestive cavity (from endoderm)
Figure 32.8a
(c) Acoelomate Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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Pseudocoelomates have a ‘fake’ coelom
Acoelomates lack a body cavity
• A pseudocoelom is a body cavity
• Organisms without body cavities
– derived from the blastocoel, not from mesoderm
– Are considered acoelomates
Body covering (from ectoderm)
Body covering (from ectoderm) (c) Acoelomate. Acoelomates such as flatworms lack a body cavity between the digestive tract and outer body wall.
(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 endoderm)
Digestive tract (from ectoderm)
Figure 32.8b Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Tissuefilled region (from mesoderm)
Figure 32.8c Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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Protostome and Deuterostome Development
Cleavage
• Based on certain features seen in early development
• In protostome development
– Most Bilaterian animals can be categorized as having one of two developmental modes: – Protostome development, first hole becomes the mouth, or
– Cleavage is spiral and determinate
• In deuterostome development – Cleavage is radial and indeterminate Protostome development (examples: molluscs, annelids, arthropods)
– Deuterostome development, second hole becomes the mouth
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.
Eight-cell stage
Spiral and determinate
Radial and indeterminate
Figure 32.9a Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Mesoderm and Coelom Formation
Fate of the Blastopore
• Protostomes form Mesoderm & the Coelom by
• In protostome development
– Schizocoelous development
– The blastopore (first hole) becomes the mouth
• Deuterostomes form Mesoderm & the Coelom by – Enterocoelous development
• In deuterostome development – The blastopore becomes the anus
Coelom
Coelom Mesoderm
Blastopore
Schizocoelous: solid masses of mesoderm split and form coelom
Mouth
Anus
Archenteron
Blastopore
Mesoderm
Digestive tube
Enterocoelous: folds of archenteron form coelom
Figure 32.9b Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Mouth
Figure 32.9c
Mouth develops from blastopore
Anus Anus develops from blastopore
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Animal Phylogenies: Divergent Hypotheses
Points of Agreement
• Phylogenetic hypotheses for the Animalia agree on major features of the tree
• All animals share a common ancestor
• Zoologists currently recognize about 35 animal phyla; mostly marine • The current debate in animal systematics differs primarily on the characters used: – Morphology & Development vs. – Molecular Data
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• Sponges are basal animals: Parazoa • Eumetazoa is a clade of animals with true tissues and guts • Most animal phyla belong to the clade Bilateria • Vertebrates (and some other phyla) belong to the clade Deuterostomia
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Animalia Phylogeny: Points of Agreement PARAZOA ‘Radiata’ P. Porifera
Disagreement over the Bilaterians
EUMETAZOA
P. Cnidaria
BILATERIA
P. Ctenophora
• The morphology-based tree divides the bilaterians into two clades: – deuterostomes and protostomes
7. Triploblastic: Three Germ Layers Endoderm, Ectoderm & Mesooderm 8. Muscle and Nervous Tissues 9. Bilateral Symmetry 10. Cephalization
Radial Symmetry?
4. Gastrulation 5. Gut 6. Diploblastic: Two Germ Layers Endoderm & Ectoderm 1.
Multicellularity: Diploid
2.
Hox Genes
3.
Embryonic Development
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• In contrast, several recent molecular studies divide the bilaterians into three clades: – deuterostomes, ecdysozoans & lophotrochozoans
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Animalia: Morphology/Developmental Phylogeny
Fig. 32-10
“Porifera”
Nematoda
Rotifera
Nemertea
Annelida
Arthropoda
Mollusca
Chordata
Platyhelminthes
Brachiopoda
Echinodermata
Phoronida
Ectoprocta
Cnidaria
Ctenophora
Ectoprocta
Deuterostomia
Porifera
Ctenophora
Brachiopoda Echinodermata
Bilateria
Deuterostomia
Eumetazoa
“Radiata”
Metazoa
ANCESTRAL COLONIAL FLAGELLATE
Cnidaria
Protostomia
Bilateria
Chordata Platyhelminthes Protostomia
Eumetazoa
Rotifera Mollusca Annelida
Metazoa
Arthropoda Ancestral colonial flagellate
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Acoela
Arthropoda
Rotifera
Annelida
Mollusca
Nemertea
Ectoprocta
Platyhelminthes
Phoronida
Brachiopoda
Chordata
Echinodermata
Cnidaria
Silicarea
Nematoda
Ecdysozoa
Bilateria
Deuterostomia
Lophotrochozoa
Bilateria
Deuterostomia
Calcarea
Cnidaria
“Radiata”
“Porifera”
Silicea
Ctenophora Eumetazoa
Ctenophora
Metazoa
ANCESTRAL COLONIAL FLAGELLATE
“Porifera”
Fig. 32-11
Animalia: Molecular Phylogeny Calcarea
Nematoda
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Echinodermata Chordata Platyhelminthes Lophotrochozoa
Eumetazoa
Rotifera Ectoprocta Brachiopoda Mollusca Annelida
Ecdysozoa
Metazoa
Ancestral colonial flagellate
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Nematoda Arthropoda
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Fig. 32-UN1
Fig. 32-9
Eumetazoa
Ctenophora Cnidaria Acoela (basal bilaterians) Deuterostomia Bilateral summetry Three germ layers
Lophotrochozoa Ecdysozoa
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• Ecdysozoans share a common characteristic – They shed their exoskeletons through a process called ecdysis
Eight-cell stage
(b) Coelom formation
Coelom
Ectoderm Mesoderm Endoderm
(a) Cleavage
Radial and indeterminate
Spiral and determinate Key
Bilateria (most animals)
True tissues
Eight-cell stage
Metazoa
Sponges (basal animals)
Deuterostome development (examples: echinoderm, chordates)
Protostome development (examples: molluscs, annelids)
Common ancestor of all animals
Archenteron Coelom Mesoderm
Blastopore
Blastopore
Solid masses of mesoderm split and form coelom.
Mesoderm
Folds of archenteron form coelom.
Anus
Mouth
(c) Fate of the blastopore
Digestive tube
Mouth Mouth develops from blastopore.
Anus Anus develops from blastopore.
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• Lophotrochozoans often share one of two common characteristics: – a lophophore (feeding structure) – a development stage: trochophore larva Apical tuft of cilia
Mouth
Anus
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Future Directions in Animal Systematics • Phylogenetic studies based on larger databases
Fig. 32.13a, b
(a) An ectoproct, a lophophorate
(b) Structure of trochophore larva
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Animalia Phylogeny: Points of Agreement PARAZOA
EUMETAZOA ‘Radiata’
P. Porifera
P. Cnidaria
P. Ctenophora
BILATERIA DEUTEROSTOMIA PROTOSTOMIA - OR Lophotrochoza / Ecdysozoa
– Will likely provide further insights into animal evolutionary history
Radial Symmetry?
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7. Triploblastic: Three Germ Layers Endoderm, Ectoderm & Mesooderm 8. Muscle and Nervous Tissues 9. Bilateral Symmetry 10. Cephalization 4. Gastrulation 5. Gut 6. Diploblastic: Two Germ Layers Endoderm & Ectoderm
1.
Multicellularity: Diploid
2.
Hox Genes
3.
Embryonic Development
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Alternate Cladogram of the Metazoa http://www.sciencedaily.com/releases/ 2009/01/090126203157.htm
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