1. Chapter 32 An Overview of Animal Diversity
Reading Questions Notes Summary

2. Animal Kingdom Characteristics
Animal are multicellular, heterotrophic eukaryotes with tissues that develop from embryonic layers
Animals are multicellular eukaryotes
Their cells lack cell walls
Their bodies are held together by structural proteins such as collagen
Nervous tissue and muscle tissue are unique, defining characteristics of animals
Tissues are groups of cells that have a common structure, function, or both

3. 1. Embryological Development Stages
Most animals reproduce sexually, with the diploid stage usually dominating the life cycle
After a sperm fertilizes an egg, the zygote undergoes rapid cell division called cleavage
Cleavage leads to formation of a multicellular, hollow blastula
The blastula undergoes gastrulation, forming a gastrula with different layers of embryonic tissues
The gastrual has a blastopore (the opening) and the archenteron ( the blind pouch)

4. Figure 32.2

5. Many animals have at least one larval stage
A larva is sexually immature and morphologically distinct from the adult; it eventually undergoes metamorphosis
A juvenile resembles an adult, but is not yet sexually mature

6. 2. What are Hox genes?
Most 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

7. Homeotic genes are regulatory genes that control the placement and spatical organization of body parts in animals, plants and fungi by controlling the developmental fate of a group of cells.. in animals were named Hox genes.

8. Hox genes (homeobox containing genes) regulate the formation of anterior – posterior axis of the animal body. (Head, thorax, abdomen,)
Homeoboxes are 180 nucleotide sequence of DNA which specifies for a 60-amino acid homeodomain in proteins These proteins in turn affect development of cells into certain body parts.

9. Hox genes in more complex animals arose through duplication of earlier homeobox genes in the genetic code.
Certain homeoboxes and homeotic genes are conserved and show up in the genetic code between different animals. (Example: drosophila, mice and humans)

10. This implies that homeoboxes arose very early in the evolution of animals and are conserved in the animal DNA.
Duplication and variation of these Hox genes allow for a versatile potential of diversity to arise in the morphology in animal evolution.

11. 3. Dominant life forms during the eras
Neoproterozoic Era (1 Billion–542 Million Years Ago)
Early members of the animal fossil record include the Ediacaran biota, which dates from 565 to 550 million years ago
Animals include sponges and cnidarians (jellyfish, coral, sea anemone)
Simple body plans
Radial symmetry
Some bilateral symmetrical animals with repeating body segments

12. Paleozoic Era (542–251 Million Years Ago)
The Cambrian explosion (535 to 525 million years ago) marks the earliest fossil appearance of many major groups of living animals
Animals included arthropods, chordates, and echinoderms
There are several hypotheses regarding the cause of the Cambrian explosion and decline of Ediacaran biota (Figure 32.5)
New predator-prey relationships
A rise in atmospheric oxygen
The evolution of the Hox gene complex

13. Animal diversity continued to increase through the Paleozoic, but was punctuated by mass extinctions
Fishes become the top predators in the marine food web
Animals began to make an impact on land by 460 million years ago
Arthropods adapted to terrestrial environments (leading to insects)

14. Vertebrates made the transition to land around 360 million years ago
Some animals have adaptations that allow them to start living on land and diversified into numerous terrestrial groups which include the amphibians (frogs and salamanders and reptiles

15. Mesozoic Era (251–65.5 Million Years Ago)
Coral reefs emerged, becoming important marine ecological niches for other organisms
The ancestors of plesiosaurs were reptiles that returned to the water
During the Mesozoic era, dinosaurs were the dominant terrestrial vertebrates
The first mammals emerged
Flowering plants and insects diversified

16. 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
These extinctions included the large, nonflying dinosaurs and the marine reptiles
Mammals increased in size and exploited vacated ecological niches
The global climate cooled

17. The Burgess Shale located in BC is famous for its fossils which document the diversity of Cambrian animals. The fossils give us a picture of the types strange animals that existed during the Cambrian explosion.

18. Animal Body Plans & Symmetry
Animals can be categorized according to the symmetry of their bodies, or lack of it
Figure 32.7
Some animals have radial symmetry, with no front and back, or left and right
Radial animals are often sessile or planktonic (drifting or weakly swimming)

19. Two-sided symmetry is called bilateral symmetry
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
Bilateral animals often move actively and have a central nervous system

20. 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
During development, three germ layers give rise to the tissues and organs of the animal embryo
Sponges and a few other groups lack true tissues
Diploblastic animals have ectoderm and endoderm
These include cnidarians and comb jellies
Triploblastic animals also have an intervening mesoderm layer; these include all bilaterians
These include flatworms, arthropods, vertebrates, and others

21. Body Cavities Most triploblastic animals possess a body cavity
A true body cavity is called a coelom and is derived from mesoderm
Coelomates are animals that possess a true coelom
A pseudocoelom is a body cavity derived from the mesoderm and endoderm
Triploblastic animals that possess a pseudocoelom are called pseudocoelomates
Triploblastic animals that lack a body cavity are called acoelomates

22. Figure 32.8

23. A coelom or body cavity has many functions:
Its fluid cushions internal organs and prevents injury
Some coelomates (such as earthworms) have coeloms that contains noncompressible fluid that acts like a skeleton against which muscles can work
A body cavity allows for internal orgnas to grow and move independently of the outer body wall (ex. Movement of heart beating, lungs expanding, rippling of intestines)

24. Coelomates and pseudocoelomates belong to the same grade because of similar body plans
Phylogenetic studies indicate that true coeloms and pseudocoeloms have been independently gained and lost multiple times over the course of animal evolution
A grade is a group whose members share key biological features
A grade is not necessarily a clade, an ancestor and all of its descendants
So these terms are useful in describing body structure but must be interpreted with caution when referring to evolutionary history of animals

25. Protostomes and Deuterostomes
Based on early development, many animals can be categorized as having protostome development or deuterostome development

26. Figure 32.9

27. Protostome vs Deuterostome : Cleavage
In protostome development, cleavage is spiral and determinate
In deuterostome development, cleavage is radial and indeterminate
With indeterminate cleavage, each cell in the early stages of cleavage retains the capacity to develop into a complete embryo
Indeterminate cleavage makes possible identical twins, and embryonic stem cells

28. Protostome vs Deuterostome : Coelom Formation
In protostome development, the splitting of solid masses of mesoderm forms the coelom
In deuterostome development, the mesoderm buds from the wall of the archenteron to form the coelom

29. Protostome vs Deuterostome : Fate of the Blastopore
The blastopore forms during gastrulation and connects the archenteron to the exterior of the gastrula
In protostome development, the blastopore becomes the mouth
In deuterostome development, the blastopore becomes the anus

30. Animal Phylogeny Zoologists recognize about three dozen animal phyla
Phylogenies now combine morphological, molecular, and fossil data
Current debate in animal systematics has led to the development of multiple hypotheses about the relationships among animal groups

31. One hypothesis of animal phylogeny is based mainly on morphological and developmental comparisons
Figure 32.10

32. One hypothesis of animal phylogeny is based mainly on molecular data
Figure 32.11

33. Most scientists think the data and research support the second view of animal phylogeny tree based mainly on molecular data
As new information emerges, our understanding of evolutionary relationships in these animal phylogeny tree models may also change
Over time models in science always change to fit new data from research in order to find a better understanding of our world.

34. Points of Agreement All animals share a common ancestor
Sponges are basal animals
Eumetazoa is a clade of animals (eumetazoans) with true tissues
Most animal phyla belong to the clade Bilateria, and are called bilaterians
Chordates and some other phyla belong to the clade Deuterostomia

35. Progress in Resolving Bilaterian Relationships
The morphology-based tree divides bilaterians into two clades: deuterostomes and protostomes
In contrast, recent molecular studies indicate three bilaterian clades: Deuterostomia, Ecdysozoa, and Lophotrochozoa

36. Ecdysozoans shed their exoskeletons through a process called ecdysis
Figure 32.12

37. Some lophotrochozoans have a feeding structure called a lophophore
Others go through a distinct developmental stage called the trochophore larva
Figure 32.13