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

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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

Figure 32.3 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

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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

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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

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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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