1. An Introduction to Animal Diversity
Chapter 32
An Introduction to Animal Diversity

2. Overview: Welcome to Your Kingdom The animal kingdom
Extends far beyond humans and other animals we may encounter
Figure 32.1

3. Several characteristics of animals
Concept 32.1: Animal are multicellular, heterotrophic eukaryotes with tissues that develop from embryonic layers
Several characteristics of animals
Sufficiently define the group

4. Animals are heterotrophs
Nutritional Mode
Animals are heterotrophs
That ingest their food

5. Cell Structure and Specialization
Animals are multicellular eukaryotes
Their cells lack cell walls

6. Their bodies are held together
By structural proteins such as collagen
Nervous tissue and muscle tissue
Are unique to animals

7. Reproduction and Development
Most animals reproduce sexually
With the diploid stage usually dominating the life cycle

8. 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

9. Cross section of blastula
Early embryonic development in animals
The zygote of an animal undergoes a succession of mitotic cell divisions called cleavage. 1
Only one cleavage
stage–the eight-cell
embryo–is shown here. 2
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. 3
Zygote
Cleavage
Eight-cell stage
Blastula
Cross section of blastula
Blastocoel
Gastrula
Gastrulation
Endoderm
Ectoderm
Blastopore
The endoderm of
the archenteron de-
velops into the tissue
lining the animal’s
digestive tract. 6
The blind pouch
formed by gastru-
lation, called
the archenteron,
opens to the outside
via 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
Figure 32.2

10. 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

11. 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
Single cell
Stalk
Figure 32.3

12. Animals can be categorized
Symmetry
Animals can be categorized
According to the symmetry of their bodies, or lack of it

13. Some animals have radial symmetry
Like in a flower pot
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)
Figure 32.7a

14. Some animals exhibit bilateral symmetry
Or two-sided symmetry
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)
Figure 32.7b

15. 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

16. Tissues Animal body plans Tissues
Also vary according to the organization of the animal’s tissues
Tissues
Are collections of specialized cells isolated from other tissues by membranous layers

17. Triploblastic animals
Animal embryos
Form germ layers, embryonic tissues, including ectoderm, endoderm, and mesoderm
Diploblastic animals
Have two germ layers
Triploblastic animals
Have three germ layers

18. In triploblastic animals
Body Cavities
In triploblastic animals
A body cavity may be present or absent

19. 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 layer
lining coelom
and suspending
internal organs
(from mesoderm)
Coelomate. Coelomates such as annelids have a true coelom, a body cavity completely lined by tissue derived from mesoderm.
(a)

20. A pseudocoelom
Is a body cavity derived from the blastocoel, rather than from mesoderm
Pseudocoelom
Muscle layer
(from
mesoderm)
Body covering
(from ectoderm)
Digestive tract
Pseudocoelomate. Pseudocoelomates such as nematodes have a body cavity only partially lined by tissue derived from mesoderm.
(b)
Figure 32.8b

21. Organisms without body cavities
Are considered acoelomates
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)
Figure 32.8c

22. 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

23. In protostome development
Cleavage
In protostome development
Cleavage is spiral and determinate
In deuterostome development
Cleavage is radial and indeterminate
Protostome development
(examples: molluscs, annelids,
arthropods)
Deuterostome development
(examples: echinoderms,
chordates)
Eight-cell stage
Spiral and determinate
Radial and indeterminate
(a) Cleavage. In general, protostome development begins with spiral, determinate cleavage. Deuterostome development is characterized by radial, indeterminate cleavage.
Figure 32.9a

24. One hypothesis of animal phylogeny based mainly on molecular data
Calcarea
Silicarea
Ctenophora
Cnidaria
Echinodermata
Chordata
Brachiopoda
Phoronida
Ectoprocta
Platyhelminthes
Nemertea
Mollusca
Annelida
Rotifera
Nematoda
Arthropoda
“Radiata”
“Porifera”
Deuterostomia
Lophotrochozoa
Ecdysozoa
Bilateria
Eumetazoa
Metazoa
Ancestral colonial
flagellate
Figure 32.11

25. Points of Agreement
All animals share a common ancestor
Sponges are basal animals
Eumetazoa is a clade of animals with true tissues

26. Most animal phyla belong to the clade Bilateria
Vertebrates and some other phyla belong to the clade Deuterostomia

27. Ecdysozoans share a common characteristic
They shed their exoskeletons through a process called ecdysis
Figure 32.12

28. The End