View
225
Download
2
Category
Preview:
Citation preview
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
IB-202-1 (3-8-06)
An Introduction to Animal Diversity
Chapter 32
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Much Diversity in the Marine Environment (Oceans)
• Overview: Welcome to Your Kingdom
• The animal kingdom
– Extends far beyond humans and other animals we may encounter
Figure 32.1
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Concept 32.1: Animal are multicellular, heterotrophic eukaryotes with tissues that develop from embryonic layers
• Several characteristics of animals
– Sufficiently define the group
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Nutritional Mode
• Animals are heterotrophs
– That ingest their food (reduced carbon)
– They lack cell walls (no cellulose)
– Their bodies are held together by structural proteins such as collagen
• Nervous tissue and muscle tissue are unique to animals
– Most animals reproduce sexually (egg and sperm with each contributing a haploid number of chromosomes to the zygote)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Cell Structure and Specialization
• Animals are multicellular eukaryotes
• Animal cells lack cellulose cell walls which means that they cannot tolerate intracellular pressure like plant cells. If they swell they will burst.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Reproduction and Development
• Most animals reproduce sexually
– With the diploid stage usually dominating the life cycle
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Zygote
Cleavage
Eight-cell stage
Cleavage
Blastula Cross section of blastula
Blastocoel
Blastocoel
Gastrula Gastrulation
Endoderm
Ectoderm
Blastopore
• Early embryonic development in animals
Figure 32.2
In most animals, cleavage results in theformation of a multicellular stage called a blastula.The blastula of many animals is a hollow ball of cells.
3
The endoderm ofthe archenteron de-
velops into the tissuelining the animal’s
digestive tract.
6
The blind pouchformed by gastru-
lation, calledthe archenteron,
opens to the outsidevia the blastopore.
5
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).
4
Only one cleavagestage–the eight-cellembryo–is shown here.
2 The zygote of an animal undergoes a succession of mitotic cell divisions called cleavage.
1
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• The common ancestor of living animals
– May have lived 1.2 billion–800 million years ago
– May have resembled modern choanoflagellates, protists that are the closest living relatives of animals
Figure 32.3
Single cell
Stalk
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
– Was probably itself a colonial, flagellated protist
Figure 32.4
Colonial protist,an aggregate ofidentical cells
Hollow sphere of unspecialized cells (shown in cross section)
Beginning of cell specialization
Infolding Gastrula-like “protoanimal”
Somatic cells Digestivecavity
Reproductive cells
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Paleozoic Era (542–251 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• The set of morphological and developmental traits that define a grade
– Are generally integrated into a functional whole referred to as a body plan
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Symmetry
• Animals can be categorized
– According to the symmetry of their bodies, or lack of it
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Some animals have radial symmetry
– Like in a flower pot
Figure 32.7a
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.
(a)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Some animals exhibit bilateral symmetry
– Or two-sided symmetry
Figure 32.7b
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.
(b)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Animal embryos
– Form germ layers, embryonic tissues, including ectoderm, endoderm, and mesoderm
• Diploblastic animals
– Have two germ layers (ectoderm & endoderm)
• Triploblastic animals
– Have three germ layers (ectoderm, endoderm and mesoderm. Mesodermal layer is derived from endoderm cells)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Body Cavities
• In triploblastic animals
– A body cavity may be present or absent
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• A true body cavity
– Is called a coelom and is derived from mesoderm
Figure 32.8a
Coelom
Body covering(from ectoderm)
Digestive tract(from endoderm)
Tissue layerlining coelomand suspendinginternal organs(from mesoderm)
Coelomate. Coelomates such as annelids have a true coelom, a body cavity completely lined by tissue derived from mesoderm.
(a)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• A pseudocoelom
– Is a body cavity derived from the blastocoel, rather than from mesoderm
Figure 32.8b
PseudocoelomMuscle layer(from mesoderm)
Body covering(from ectoderm)
Digestive tract(from ectoderm)
Pseudocoelomate. Pseudocoelomates such as nematodes have a body cavity only partially lined by tissue derived from mesoderm.
(b)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Organisms without body cavities
– Are considered acoelomates
Figure 32.8c
Body covering(from ectoderm) Tissue-
filled region(from mesoderm)
Digestive tract(from endoderm)
Acoelomate. Acoelomates such as flatworms lack a body cavity between the digestive tract and outer body wall.
(c)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Developmental Patterns (Deuterostome andProtostome)
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Cleavage
• In protostome development
– Cleavage is spiral and determinate
• In deuterostome development
– Cleavage is radial and indeterminate
Figure 32.9a
Protostome development(examples: molluscs, annelids,
arthropods)
Deuterostome development(examples: echinoderms,
chordates)
Eight-cell stage Eight-cell stage
Spiral and determinate Radial and indeterminate
(a) Cleavage. In general, protostomedevelopment begins with spiral, determinate cleavage.Deuterostome development is characterized by radial, indeterminate cleavage.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Figure 32.9b
Archenteron
Blastopore MesodermCoelom
BlastoporeMesoderm
Schizocoelous: solidmasses of mesodermsplit and form coelom
Enterocoelous:folds of archenteronform coelom
Coelom (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).
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Fate of the Blastopore
• In protostome development
– The blastopore becomes the mouth
• In deuterostome development
– The blastopore becomes the anus
Figure 32.9c
Anus
Anus
Mouth
Mouth
Mouth developsfrom blastopore
Anus developsfrom blastopore
Digestive tube
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• One hypothesis of animal phylogeny based mainly on morphological and developmental comparisons
Figure 32.10
Po
rife
ra
Cn
ida
ria
Cte
no
ph
ora
Ph
oro
nid
a
Ect
op
roc
ta
Bra
ch
iop
od
a
Ech
ino
de
rmat
a
Ch
ord
ata
Pla
tyh
elm
inth
es
Mo
llu
sca
An
nel
ida
Art
hro
po
da
Ro
tife
ra
Ne
me
rte
a
Ne
ma
tod
a
“Radiata” Deuterostomia Protostomia
Bilateria
Eumetazoa
Metazoa
Ancestral colonialflagellate
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• One hypothesis of animal phylogeny based mainly on molecular data
Figure 32.11
Ca
lcar
ea
Sili
care
a
Cte
no
ph
ora
Cn
ida
ria
Ech
ino
de
rmat
a
Ch
ord
ata
Bra
ch
iop
od
a
Ph
oro
nid
a
Ect
op
roc
ta
Pla
tyh
elm
inth
es
Ne
me
rte
a
Mo
llu
sca
An
nel
ida
Ro
tife
ra
Ne
ma
tod
a
Art
hro
po
da
“Radiata”
“Porifera” Deuterostomia Lophotrochozoa Ecdysozoa
Bilateria
Eumetazoa
Metazoa
Ancestral colonialflagellate
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Points of Agreement
• All animals share a common ancestor
• Sponges are basal animals
• Eumetazoa is a clade of animals with true tissues
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Most animal phyla belong to the clade Bilateria
• Vertebrates and some other phyla belong to the clade Deuterostomia
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Ecdysozoans share a common characteristic
– They shed their exoskeletons through a process called ecdysis
Figure 32.12
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Lophotrochozoans share a common characteristic
– Called the lophophore, a feeding structure
• Other phyla
– Go through a distinct larval stage called a trochophore larva
Figure 32.13a, b
Apical tuftof cilia
Mouth
Anus(a) An ectoproct, a lophophorate (b) Structure of trochophore larva
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Future Directions in Animal Systematics
• Phylogenetic studies based on larger databases
– Will likely provide further insights into animal evolutionary history
Recommended