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Chapter 32 An Introduction to Animal Diversity
1. What is an animal?
- Multicellular, heterotrophic eukaryote – ingestion
- Structural support from structural proteins – NOT cell walls
- Nervous tissue & muscle tissue for impulse conduction & movement
- Sexual reproduction with motile sperm swimming to non-motile egg
2. How did animals evolve?
- Current animal development
Figure 32.2 Early embryonic development in animals (layer 1)
Cleavage
Zygote
Eight-cell stage
Cleavage – cell division w/out cytokinesis
- More cells but same total volume – no cell growth
Figure 32.2 Early embryonic development in animals (layer 2)
Blastocoel
Cleavage
Cleavage
Zygote
Eight-cell stage
Blastula
Cross section
of blastula
Blastula – hollow ball of cells
-coel – opening or cavity
Figure 32.2 Early embryonic development in animals (layer 3)
Blastocoel
Cleavage
Cleavage
Zygote
Eight-cell stage
Blastula
Blastocoel
Cross section
of blastula
Endoderm
Ectoderm
Gastrula
Blastopore
Gastrulation
Gastrulation – movement of cells to form 2 layers
Blastopore – opening where cells move into
Ectoderm – outside layer
Endoderm – inside layer
Chapter 32 An Introduction to Animal Diversity
1. What is an animal?
- Multicellular, heterotrophic eukaryote – ingestion
- Structural support from structural proteins – NOT cell walls
- Nervous tissue & muscle tissue for impulse conduction & movement
- Sexual reproduction with motile sperm swimming to non-motile egg
2. How did animals evolve?
- Current animal development
- Current hypothesis
Figure 32.4 One hypothesis for the origin of animals from a
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
Infolding
Gastrula-like
“protoanimal”
Chapter 32 An Introduction to Animal Diversity
1. What is an animal?
2. How did animals evolve?
3. How are animals grouped & characterized?
- Body plans
- Symmetry
- None (sponge)
- Radial
- multiple central axis “cuts” provide mirror images
- Only have top & bottom
- Bilateral
- Only 1 central axis “cut” provides a mirror image
- Has top, bottom, left & right
Radial
Bilateral
Chapter 32 An Introduction to Animal Diversity
1. What is an animal?
2. How did animals evolve?
3. How are animals grouped & characterized?
- Body plans
- Symmetry & TISSUES
- None (sponge)
- Radial
- multiple central axis “cuts” provide mirror images
- Only have top & bottom
- Diploblastic – 2 cell layers
- Ectoderm
- Endoderm
- Bilateral
- Only 1 central axis cut provides a mirror image
- Has top, bottom, left & right
- Triploblastic – 3 cell layers
- Ectoderm & endoderm
- Mesoderm – in between ecto- & endoderm
- Cephalization – movement of sensory equipment towards the
anterior end of the organism – associated with movement
Chapter 32 An Introduction to Animal Diversity
1. What is an animal?
2. How did animals evolve?
3. How are animals grouped & characterized?
- Body plans
- Symmetry & tissues
- Body cavities
- Acoelomates – without a body cavity
- Pseudocoelomates – “false body cavity” – cavity not completely
lined with tissue derived from mesoderm
- Coelomates – body cavity completely lined with tissue
from mesoderm
Figure 32.8 Body plans of triploblastic animals
Coelom
(a) Coelomate. Coelomates such as
annelids have a true coelom, a body
cavity completely lined by tissue
derived from mesoderm.
Body covering
(from ectoderm)
Digestive tract
(from endoderm)
Tissue layer
lining coelom
and suspending
internal organs
(from mesoderm)
Body covering
(from ectoderm)
(b) Pseudocoelomate. Pseudocoelomates
such as nematodes have a body cavity only
partially lined by tissue derived from
mesoderm.
Muscle layer
(from
mesoderm)
Pseudocoelom
Digestive tract
(from ectoderm)
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)
Tissuefilled region
(from
mesoderm)
Chapter 32 An Introduction to Animal Diversity
1. What is an animal?
2. How did animals evolve?
3. How are animals grouped & characterized?
- Body plans
- Symmetry & tissues
- Body cavities
- Developmental plan
- Protostome
- Deuterostome
Figure 32.9 A comparison of protostome and deuterostome
development
Protostome development
(examples: molluscs, annelids,
arthropods)
Deuterostome development
(examples: echinoderms,
chordates)
(a)
Eight-cell stage
Eight-cell stage
Spiral and determinate
Cleavage. In general, protostome
development begins with spiral,
determinate cleavage. Deuterostome
development is characterized by radial,
indeterminate cleavage.
Radial and indeterminate
(b)
Coelom
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).
Archenteron
Coelom
Mesoderm
Blastopore
Blastopore
Schizocoelous: solid
masses of mesoderm
split and form coelom
Mesoderm
Enterocoelous:
folds of archenteron
form coelom
Mouth
Anus
Digestive tube
Mouth
Mouth develops
from blastopore
Anus
Anus develops
from blastopore
(c)
Fate of the blastopore. In protostome
development, the mouth forms from the
blastopore. In deuterostome
development, the mouth forms from a
secondary opening.
“Radiata”
Deuterostomia
Metazoa
Ancestral colonial
flagellate
Nematoda
Nemertea
Rotifera
Arthropoda
Annelida
Protostomia
Bilateria
Eumetazoa
Mollusca
Platyhelminthes
Chordata
Echinodermata
Brachiopoda
Ectoprocta
Phoronida
Ctenophora
Cnidaria
Porifera
Figure 32.10 One hypothesis of animal phylogeny based mainly
on morphological and developmental comparisons
Arthropoda
Nematoda
Rotifera
Annelida
Mollusca
Nemertea
Platyhelminthes
Ectoprocta
Phoronida
Brachiopoda
Chordata
Echinodermata
Cnidaria
Ctenophora
Silicarea
Calcarea
Figure 32.11 One hypothesis of animal phylogeny based mainly
on molecular data
“Radiata”
“Porifera”
Deuterostomia
Lophotrochozoa
Bilateria
Eumetazoa
Metazoa
Ancestral colonial
flagellate
Ecdysozoa
Figure 32.12 Ecdysis
Ecdysozoa – secrete an exoskeleton and molt
Nematoda & Arthropoda
Figure 32.13 Characteristics of lophotrochozoans
Apical tuft
of cilia
100 m
Mouth
(a)
Anus
An ectoproct, a lophophorate
(b)
Structure of trochophore larva