Chapter 32

1. Chapter 32 An Introduction to Animal Diversity

2. Modes of Nutrition • Animals differ in their mode of nutrition than plants and fungi. • Animals and fungi are heterotrophic. • Plants are autotrophic. • Fungi release exoenzymes. • Animals ingest their food. • They release enzymes to break down their food.

3. Animal Cells • Animal cells lack cell walls. • Fungi have them-- • Plants have them-- • The structural integrity of animal bodies is due to proteins--collagen. • Tight junctions, gap junctions, and desmosomes. • Muscle cells and nerve cells are also found in animals.

5. Animal Reproduction • Animals reproduce mostly via sexual reproduction. • Life cycle dominated by the diploid stage. • Usually a small, haploid, flagellated sperm fertilizes a non-motile egg forming a diploid zygote.

6. Cell Division • Cell Division is known as cleavage

7. Changes in the Zygote • After fertilization, the zygote undergoes cleavage. • Successive mitotic divisions with no cell growth. • This division leads to the formation of the blastula.

8. The Blastula • Is a hollow ball of animal cells. • The blastula then becomes the gastrula.

9. The Gastrula • The gastrula is the stage that gives rise to embryonic tissues. • The embryonic tissues eventually develop into adult body parts.

10. Stages of Development • Some animals go through transient stages of development. • Many of them go through at least 1 larval stage. • A larva is a sexually immature form of an animal that is morphologically distinct from the adult. • Frogs and flies are examples.

11. Stages of Development • Recall the importance of the homeobox genes. • Hox genes control the segmentation pattern in animals. • They are the result of many successive gene duplications throughout evolution. • They play important roles in the development and differentiation of animals. • They produce many of the observed morphological features.

12. Body Plans • Body plans are morphological traits or organizational plans that are shared by a group of animal species.

13. Symmetry • Some animals have symmetry, others don’t. • Radial symmetry--top and bottom, but no front and back. • Bilateral symmetry--top and bottom, front and back.

15. Tissues • The body plans of animals also varies according to tissue organization. • Tissues are collections of specialized cells separated from other tissues by membranous layers. • Tissues form after gastrulation has taken place.

16. Tissues • Development gives rise to germ layers which form the various tissues and organs of the body. • Ectoderm--outer portion of body--skin. • Endoderm--innermost layer. Lines the developing digestive tube. The lining of the digestive tract and organs derived from it.

17. Germ Layers • Ectoderm and endoderm are the previously mentioned germ layers. • Animals with just these two are called diploblasts. • Sponges and Coelenterates • Animals that have a third germ layer, the mesoderm, are called triploblasts. • Mesoderm forms the muscles and most other organs between the digestive tube and the outside of the animal.

18. Body Cavities • Some triploblasts have a body cavity filled with fluid. • Called a coelom; derived from mesoderm. • It separates the digestive tract from the outer body wall. • Animals with a coelom are called coelomates.

19. Body Cavities • Some triploblasts form a body cavity from the blastocoel rather than the mesoderm. • This cavity is functional and is called a pseudocoelom. • These animals are called pseudocoelomates.

20. Body Cavities • Some triploblasts lack a coelom altogether. • There is no body cavity between the digestive tract and the outer body wall. • These are called acoelomates.

22. Protostomes and Deuterostomes • Many animals can be classified as either protostomes or deuterostomes. • Three features distinguish their development: • 1. Cleavage • 2. Coelom Formation • 3. Fate of the Blastopore

23. Cleavage • Many protostomes have spiral cleavage. • Cleavage diagonal to the vertical axis of the embryo. • The 8-cell stage has smaller cells which lie in the grooves between the larger underlying cells.

24. Cleavage • This so-called determinant cleavage of some animals determines the developmental fate of each embryonic cell very early.

25. Cleavage • Radial cleavage is common in deuterostomes. • You either see cleavage planes parallel or perpendicular to the vertical axis of the embryo. • Here, the tiers of the cells are aligned.

26. Cleavage • Most deuterostomes have indeterminant cleavage. • This means that each cell in the embryo can fully develop into a complete embryo. • This makes identical twins possible. • This is why 4-cell stage sea stars can be divided to give 4 larvae. • This is why embryonic stem cells have the capacity to perform so many functions.

27. Deuterostomes • Have radial cleavage • Their archenteron gives rise to the coelom • The mouth arises from the end of the embryo opposite the blastopore. • (The blastopore becomes the anus)

28. The Archenteron • This is the endoderm-lined cavity that forms during animal development (gastrulation) and gives rise to the digestive tract.

29. Coelom Formation • In protostome development, as the archenteron forms during gastrulation, the mesoderm splits forming a coelomic cavity.

30. Coelom Formation • During deuterostome development, the mesoderm buds off of the wall of the archenteron. • This cavity becomes the coelom.

31. Fate of the Blastopore • This is the fundamental characteristic that distinguishes protostome and deuterostome development. • The blastopore is the indentation that leads to the formation of the archenteron.

32. Protostomes • After the archenteron develops, a second opening forms at the opposite end of the gastrula. • Now there are two openings.

33. Protostomes • In protostomes, the mouth develops from the first opening--the blastopore. • The anus develops from the second opening.

34. Deuterostomes • In deuterostomes, the mouth develops from the second opening. • The blastopore (first opening) becomes the anus.