1. Overview: Welcome to Your Kingdom
The animal kingdom extends far beyond humans and other animals we may encounter
Video: Coral Reef

3. Several characteristics, taken together, sufficiently define the group
Concept 32.1: Animal are multicellular, heterotrophic eukaryotes with tissues that develop from embryonic layers
There are exceptions to nearly every criterion for distinguishing animals from other life forms
Several characteristics, taken together, sufficiently define the group

4. 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. Video: Sea Urchin Embryonic Development
After a sperm fertilizes an egg, the zygote undergoes cleavage, leading to formation of a blastula
The blastula undergoes gastrulation, forming embryonic tissue layers and a gastrula
Video: Sea Urchin Embryonic Development

9. LE 32-2_3 Blastocoel Cleavage Cleavage Zygote Eight-cell stage
Blastula
Cross section
of blastula
Blastocoel
Endoderm
Ectoderm
Gastrula
Gastrulation
Blastopore

10. Many animals have at least one larval stage
A larva is sexually immature and morphologically distinct from the adult; it eventually undergoes metamorphosis

11. Concept 32.2: The history of animals may span more than a billion years
The animal kingdom includes not only great diversity of living species but also the even greater diversity of extinct ones
The common ancestor of living animals may have lived 1.2 billion–800 million years ago
This ancestor may have resembled modern choanoflagellates, protists that are the closest living relatives of animals

12. Concept 32.3: Animals can be characterized by “body plans”
Zoologists sometimes categorize animals according to morphology and development
A grade is a group of animal species with the same level of organizational complexity
A body plan is the set of traits defining a grade

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

14. Some animals have radial symmetry, the form found in a flower pot

15. LE 32-7a
Radial symmetry

16. The two-sided symmetry seen in a shovel is an example of bilateral symmetry

17. LE 32-7b
Bilateral symmetry

18. 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

19. 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

20. Animal embryos have concentric layers called germ layers that form tissues and organs
Ectoderm is the germ layer covering the embryo’s surface
Endoderm is the innermost germ layer
Diploblastic animals have ectoderm and endoderm
Triploblastic animals also have an intervening mesoderm layer

21. Body Cavities
In triploblastic animals, a body cavity may be present or absent
A true body cavity is called a coelom and is derived from mesoderm

22. Coelom Body covering (from ectoderm) Tissue layer lining coelom
LE 32-8a
Coelom
Body covering
(from ectoderm)
Tissue layer
lining coelom
and suspending
internal organs
(from mesoderm)
Digestive tract
(from endoderm)
Coelomate

23. A pseudocoelom is a body cavity derived from the blastocoel, rather than from mesoderm

24. Body covering (from ectoderm) Pseudocoelom Muscle layer (from
LE 32-8b
Body covering
(from ectoderm)
Pseudocoelom
Muscle layer
(from
mesoderm)
Digestive tract
(from endoderm)
Pseudocoelomate

25. Acoelomates are organisms without body cavities

26. Wall of digestive cavity (from endoderm)
LE 32-8c
Body covering
(from ectoderm)
Tissue-
filled region
(from
mesoderm)
Wall of digestive cavity
(from endoderm)
Acoelomate

27. Protostome and Deuterostome Development
Based on early development, many animals can be categorized as having protostome or deuterostome development

28. Cleavage In protostome development, cleavage is spiral and determinate
In deuterostome development, cleavage is radial and indeterminate

29. Protostome development (examples: molluscs, annnelids, arthropods)
LE 32-9a
Protostome development
(examples: molluscs,
annnelids, arthropods)
Deuterostome development
(examples: echinoderms,
chordates)
Cleavage
Eight-cell stage
Eight-cell stage
Spiral and determinate
Radial and indeterminate

30. Coelom Formation
In protostome development, the splitting of 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

31. Protostome development (examples: molluscs, annnelids, arthropods)
LE 32-9b
Protostome development
(examples: molluscs,
annnelids, arthropods)
Deuterostome development
(examples: echinoderms,
chordates)
Coelom formation
Coelom
Archenteron
Coelom
Mesoderm
Blastopore
Blastopore
Mesoderm
Schizocoelous: solid
masses of mesoderm
split and form coelom
Enterocoelous:
folds of archenteron
form coelom

32. Fate of the Blastopore
In protostome development, the blastopore becomes the mouth
In deuterostome development, the blastopore becomes the anus

33. Protostome development (examples: molluscs, annnelids, arthropods)
LE 32-9c
Protostome development
(examples: molluscs,
annnelids, arthropods)
Deuterostome development
(examples: echinoderms,
chordates)
Fate of the blastopore
Anus
Mouth
Digestive tube
Mouth
Anus
Mouth develops
from blastopore
Anus develops
from blastopore