Download What is an animal?

Chapter 32
An Introduction to Animal
Diversity
PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
What is an animal?
• Animals are multicellular, heterotrophic eukaryotes
with tissues that develop from embryonic layers.
Several characteristics of animals sufficiently define
the group:
–
Animals are heterotrophs that ingest their food
–
Animals are multicellular eukaryotes
–
The cell wall of animals LACKS a cell wall
–
Animal bodies are held together by structural proteins such as
collagen
–
Nervous tissue and muscle tissue are unique to animals
–
Most animals reproduce sexually with the diploid stage usually
dominating the life cycle
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Cleavage & Gastrulation in Animals
• After a sperm fertilizes an egg the zygote undergoes
cleavage, leading to the formation of a blastula
– Cleavage is the process of cytokinesis in animal
cells, characterized by pinching of the plasma
membrane – and the succession of rapid cell
divisions without growth during early embryonic
development – CONVERTS ZYGOTE INTO A BALL
OF CELLS
– A blastula is a hollow ball of cells marking the end
stage of cleavage during early embryonic
development
• 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
stage–the eight-cell
embryo–is 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
Cleavage
6 The endoderm of
the archenteron develops into the tissue
lining the animal’s
digestive tract.
Zygote
Eight-cell stage
Blastula
Cross section
of blastula
Blastocoel
Endoderm
5 The blind pouch
formed by gastrulation, called
the archenteron,
opens to the outside
via the blastopore.
Ectoderm
Gastrula
Gastrulation
Blastopore
Figure 32.2
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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).
Hox Genes
• All animals, and only animals have Hox genes that
regulate the development of body form
– Hox genes are special regulatory genes that control
the transformation of a zygote to an animal of specific
form
• Hox genes are responsible for the development of
“body parts” in animals – they specify the position of
the body part on the developing embryo.
• Mutations in hox genes result in the conversion of one
body part to another.
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Common Ancestor of Living Animals
– The common ancestor of living animals was
probably itself a colonial, flagellated protist
Digestive
cavity
Somatic cells
Reproductive cells
Colonial protist,
an aggregate of
identical cells
Hollow sphere of
unspecialized
cells (shown in
cross section)
Beginning of cell
specialization
Figure 32.4
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Infolding
Gastrula-like
“protoanimal”
Paleozoic Era (542–251 Million Years Ago)
• The Cambrian explosion marks the earliest
fossil appearance of many major groups of
living animals
Figure 32.6
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Mesozoic Era (251–65.5 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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Animal Body Plans
• 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
– 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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Body Symmetry in Animals
• Animals can be categorized
– According to the symmetry of their bodies, or
lack of it
– Radial v/s Bilateral
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Radial Symmetry
• Some animals have radial symmetry
– Like in a flower pot – these organisms are
typically sessile in their environment
(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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Bilateral Symmetry
• 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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Bilateral Animals
• Bilaterally symmetrical animals have
– A dorsal (top) side and a ventral (bottom) side
– A right and left side
– Anterior (head) and posterior (tail) ends
• Bilateral Symmetry facilitates cephalization,
the development of a head – an evolutionary
trend toward the concentration of sensory
equipment on the anterior end (toward the
head)
– Bilateral organisms are typically motile in their
environment
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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
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Germ Layer Formation during Gastrulation
• Animal embryos form germ layers (embryonic tissues),
including ectoderm, endoderm, and mesoderm
– Ectoderm covers the surface of the embryo and gives
rise to the outer covering of the animal
– Endoderm is the innermost germ layer which lines the
digestive tract and organs
– Mesoderm lies between the endoderm and the
ectoderm – it forms muscles and most other organs
between the digestive tube and outer covering of the
animal
• 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
– A body cavity is a “tube-within-a-tube” body
plan consisting of a fluid-filled space
separating the digestive tract from the outer
body wall.
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Coelomates
• A true body cavity is called a coelom and is
derived from and completely lined with
mesoderm
–
Annelids, Mollusks, Arthropods, Echinoderms, and Chordates
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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Body covering
(from ectoderm)
Pseudocoelomates
• A pseudocoelom is a body cavity derived from
the blastocoel, rather than from mesoderm –
this body cavity is NOT completely lined with
mesoderm
–
Nematodes & Rotifers
Body covering
(from ectoderm)
Pseudocoelom
(b) Pseudocoelomate. Pseudocoelomates
such as nematodes have a body cavity only
partially lined by tissue derived from
mesoderm.
Digestive tract
(from ectoderm)
Figure 32.8b
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Muscle layer
(from
mesoderm)
Acoelomates
• Organisms without body cavities are
considered acoelomates – this is a “solid” body
plan
–
Platyhelminthes (flatworms)
Body covering
(from ectoderm)
(c) Acoelomate. Acoelomates such as
flatworms lack a body cavity between
the digestive tract and outer body wall.
Digestive tract
(from endoderm)
Figure 32.8c
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Tissuefilled region
(from
mesoderm)
Feeding Systems in Coelomates and Acoelomates
• Acoelomates, such as flatworms, have a gastrovascular
cavity with only one opening – which serves as a dual role
of mouth and anus.
–
This means that they lack a digestive tract altogether and absorb
nutrients across their body surface. There is no specialization of
compartments in this system.
–
Digestion is extracellular – meaning that the breakdown of food is
outside the cells.
• Coelomates, such as annelids, have a complete digestive
tract that includes specialization along the tract.
–
This means that the digestive tube extends between two
openings, the mouth and an anus.
–
Digestion is extracellular – meaning that the breakdown of food is
outside the cells.
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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
Spiral and determinate
Deuterostome development
(examples: echinoderms,
chordates)
Eight-cell stage
Radial and indeterminate
Figure 32.9a
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(a) Cleavage. In general, protostome
development begins with spiral,
determinate cleavage.
Deuterostome development is
characterized by radial, indeterminate
cleavage.
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
enterocoelous development
Coelom
Archenteron
Coelom
Mesoderm
Blastopore
Mesoderm
Blastopore
Enterocoelous:
Schizocoelous: solid
folds of archenteron
masses of mesoderm
form coelom
split and form coelom
Figure 32.9b
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(b) Coelom formation. Coelom
formation begins in the gastrula
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).
Fate of the Blastopore
• In protostome development
– The blastopore becomes the mouth
• In deuterostome development
– The blastopore becomes the anus
Mouth
Anus
Digestive tube
Mouth
Figure 32.9c
Mouth develops
from blastopore
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Anus
Anus develops
from blastopore
Embryonic Develop: Overview
• Embryonic development consists of three
stages: cleavage, gastrulation, and
organogenisis.
• Cleavage: rapid mitotic division of zygote
occurring immediately after fertilization
• Two Patterns: protostomes (spiral and
determinate) and deuterostomes (radial and
indeterminate)
• In both groups, cleavage produces a fluidfilled ball of cells called a blastula. Cells of
blastula are called blastomeres, and the
fluid filled center is called the blastocoel.
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Embryonic Develop: Overview
• Gastrulation is a process that involves
rearrangement of the blastula and begins with
the formation of the blastopore (an opening into
the blastula).
– Blastopore becomes mouth in protostomes
and anus in deuterostomes
– Some cells on the surface of the embryo may
migrate into the blastopore to form a new
cavity called the archenteron or “primitive gut”
– As a result of this cell movement, a threelayered embryo called a gastrula is formed
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Embryonic Develop: Overview
• In most animals, the gastrula consists of three
differentiated layers called the embryonic germ
layers, each of which develops into all parts of
the adult animal:
– Endoderm – forms viscera including lungs,
liver, and digestive organs
– Ectoderm – becomes skin and nervous system
– Mesoderm – gives rise to muscles, blood, and
bones
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Embryonic Develop: Overview
•
Organogenesis is the process by which cells continue to differentiate,
producing organs from the three embryonic germ layers
–
Once all organ systems have been developed, the embryo simply
increases in size
–
http://bcs.whfreeman.com/thelifewire/content/chp20/2002001.
html
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Order of Operations
• As far as the AP Biology exam is concerned,
the order of the stages and the various events
is extremely important:
• Zygote→Cleavage →Blastula →Gastrula →Organogenesis
• You should know the order of the events and a description of
each phase!
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Classifying Animals
• Most animal phyla belong to the clade Bilateria
• Vertebrates and some other phyla belong to
the clade Deuterostomia
• 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
• Ecdysozoans share a common characteristic
– They shed their exoskeletons through a
process called ecdysis
Figure 32.12
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Lophotrochozoans
• Lophotrochozoans share a common characteristic
called the lophophore, a feeding structure
• Other phyla go through a distinct larval stage
called a trochophore larva
Apical tuft
of cilia
Mouth
Figure 32.13a, b
(a) An ectoproct, a lophophorate
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Anus
(b) Structure of trochophore larva
Morphological Phylogenetic Tree
“Radiata”
Deuterostomia
Metazoa
Figure 32.10
Ancestral colonial
flagellate
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Nematoda
Nemertea
Rotifera
Arthropoda
Annelida
Protostomia
Bilateria
Eumetazoa
Mollusca
Platyhelminthes
Chordata
Echinodermata
Brachiopoda
Ectoprocta
Phoronida
Ctenophora
Cnidaria
Porifera
• One hypothesis of animal phylogeny based
mainly on morphological and developmental
comparisons
Molecular Phylogenetic Tree
Arthropoda
Nematoda
Rotifera
Annelida
Mollusca
Nemertea
Platyhelminthes
Ectoprocta
Phoronida
Brachiopoda
Chordata
Echinodermata
Cnidaria
Ctenophora
Silicarea
Calcarea
• One hypothesis of animal phylogeny based
mainly on molecular data
“Radiata”
“Porifera”
Deuterostomia
Lophotrochozoa
Bilateria
Eumetazoa
Metazoa
Figure 32.11
Ancestral colonial
flagellate
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Ecdysozoa