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
Video: Coral Reef

4. 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

5. Nutritional Mode
Animals are heterotrophs that ingest their food

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

7. Their bodies are held together by structural proteins such as collagen
Nervous tissue and muscle tissue are unique to animals

8. Reproduction and Development
Most animals reproduce sexually, with the diploid stage usually dominating the life cycle

9. 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

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

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

12. 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

13. 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

14. LE 32-3
Single cell
Stalk

15. LE 32-4 Somatic cells Digestive cavity Reproductive cells
Hollow sphere
of unspecialized
cells (shown in
cross section)
Colonial protist,
and aggregate of
identical cells
Beginning of cell
specialization
Infolding
Gastrula-like
“protoanimal”

16. Neoproterozoic Era (1 Billion–524 Million Years Ago)
Early members of the animal fossil record include the Ediacaran fauna

18. Paleozoic Era (542–251 Million Years Ago)
The Cambrian explosion marks the earliest fossil appearance of many major groups of living animals
There are several hypotheses regarding the cause of the Cambrian explosion

20. 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

21. Cenozoic Era (65.5 Million Years Ago to the Present)
The beginning of the Cenozoic era followed mass extinctions of both terrestrial and marine animals
Modern mammal orders and insects diversified during the Cenozoic

22. 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

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

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

25. LE 32-7a
Radial symmetry

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

27. LE 32-7b
Bilateral symmetry

28. 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

29. 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

30. 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

31. 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

32. 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

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

34. 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

35. Acoelomates are organisms without body cavities

36. 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

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

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

39. 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

40. 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

41. 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

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

43. 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

44. Concept 32.4: Leading hypotheses agree on major features of the animal phylogenetic tree
Zoologists recognize about 35 animal phyla
Current debate in animal systematics has led to the development of two phylogenetic hypotheses, but others exist as well

45. One hypothesis of animal phylogeny based mainly on morphological and developmental comparisons

46. LE 32-10 “Radiata” Deuterostomia Protostomia Bilateria Eumetazoa
Porifera
Cnidaria
Ctenophora
Phoronida
Ectoprocta
Brachiopoda
Echinodermata
Chordata
Platyhelminthes
Mollusca
Annelida
Arthropoda
Rotifera
Nemertea
Nematoda
“Radiata”
Deuterostomia
Protostomia
Bilateria
Eumetazoa
Metazoa
Ancestral colonial
flagellate

47. One hypothesis of animal phylogeny is based mainly on molecular data

48. LE 32-11 “Radiata” “Porifera” Deuterostomia Lophotrochozoa Bilateria
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

49. Points of Agreement All animals share a common ancestor
Sponges are basal animals
Eumetazoa is a clade of animals with true tissues
Most animal phyla belong to the clade Bilateria
Vertebrates and some other phyla belong to the clade Deuterostomia

50. Disagreement over the Bilaterians
The morphology-based tree divides bilaterians into two clades: deuterostomes and protostomes
In contrast, recent molecular studies assign two sister taxa to protostomes: the ecdysozoans and the lophotrochozoans

51. Ecdysozoans shed their exoskeletons through a process called ecdysis

53. Lophotrochozoans have a feeding structure called a lophophore
Other phyla go through a distinct larval stage called a trochophore larva

54. An ectoproct, a lophophorate Structure of trochophore larva
LE 32-13
Apical tuft
of cilia
Mouth
100 µm
Anus
An ectoproct, a lophophorate
Structure of trochophore larva

55. Future Directions in Animal Systematics
Phylogenetic studies based on larger databases will likely provide further insights into animal evolutionary history