1. CHAPTER 32 AN INTRODUCTION TO ANIMAL DIVERSITY
Prepared by
Brenda Leady, University of Toledo
Copyright (c) The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2. Characteristics Multicellular heterotroph Lack cell walls
Most have nerves, muscles, capacity to move at some point in the life cycle
Ability to reproduce sexually
Specialized sensory structures and nervous system
Cells exist in extensive extracellular matrix
Unique cell junctions

3. Traditional classifications
Most biologists agree kingdom is monophyletic
Animal genomes are very similar
Most likely ancestor a colonial flagellated protist similar to choanoflagellates
About 35 recognized animal phyla

5. Traditional classification based on body plans
4 main morphological and developmental features used
Presence or absence of different tissue types
Type of body symmetry
Presence or absence of a true body cavity
Patterns of embryonic development

6. Tissues
Metazoa divided into Parazoa (no specialized tissues or organs) and Eumetazoa (more than one type of tissue and organs)
Symmetry
Eumetazoa are radially symmetrical (Radiata) or bilaterally symmetrical (Bilateria)
Bilateral animals have cephalization and dorsal and ventral ends
Radial animals have oral and aboral sides

8. Number of cell layers Radial animals have 2 embryonic cell layers
Diplobalstic
Bilateral animals have 3 germ layers
Triploblastic
Cell layers develop during gastrulation
Inner layer – endoderm
Outer layer – ectoderm
Mesoderm - 3rd layer in bilateral animals
Forms muscles and most other organs

10. Body cavity
True coelom – body cavity is completely lined with mesoderm (coelomates)
Pseudocoelom – coelom is not completely lined by tissue derived from mesoderm (pseudicoelomates)
Acoelomates – lack a body cavity entirely
Fluid-filled body cavity can protect internal organs or be used as hydrostatic skeleton

12. Embryonic development
Cleavage in the zygote can be spiral (protostomes) or radial (deuterostomes)
Protostome
Cleavage determinate
Blastopore becomes mouth
Schizocoelous coelom development
Deuterostome
Cleavage is indeterminate- pluripotent stem cells
Blastopore becomes anus
Enterocoleus coleom development

14. Other methods of classification
Possession of exoskeleton
Development of notochord
Presence or absence of metamerism (segmentation)
Traced to changes in Hox genes

16. Changes in Hox Gene Expression Control Body Segment Specialization
Based on relatively simple changes in the expression patterns of Hox genes
Hox genes designated 1-13
Shifts in patterns of gene expression in the embryo along the anteroposterior axis govern transition from one type of vertebra to another and short or long necks
Mice, chicken, goose, and snake
Illustrates descent with modification

18. Molecular views of animal diversity
Now using new molecular techniques to classify animals by comparing similarities in the DNA and the ribosomal RNA of animals, especially sequences of nucleotides in the gene that encodes RNA of the small ribosomal subunit (SSU rRNA)
Advantage generally more objective and subject to more rigorous testing

20. Aguinaldo and Colleagues Used 18S rDNA to Analyze the Taxonomic Relationships of Arthropods to Other Taxa
Sequenced the complete gene encoding SSU rRNA
Relationships among 50 species determined
Data indicated existence of monophyletic clade- the Ecdysozoa – containing arthropods, nematodes and a number of smaller phyla
Ramifications of studies involving Drosophila melanogaster and Caenorhabditis elegans

22. Similarities between traditional and molecular phylogeny
The clade called Metazoa is monophyletic, meaning all animals came from a single common ancestor.
At the earliest stages of evolution, molecular phylogeny supports the traditional view of the split between Parazoa and Eumetazoa.
There is also agreement about an early split between Radiata and Bilateria, with most animal phyla belonging to the Bilateria.
Molecular phylogeny also agrees that the echinoderms and chordates belong to a clade called the Deuterostomia.

23. 2 key differences between traditional and molecular phylogeny
Division of protostomes into 2 clades
Traditionally split into Deuterostomia and Protostomia based on embryonic development
Deuterostomes still separate but protostomes divided into Lophotrochozoa and Ecdysozoa
Presence or absence of a body cavity
Traditionally split into coelomates, pseudocoelomates and acoelomates
Molecular evidence indicates presence or absence not a useful characteristic