What is an animal?

1. What is an animal?

2. Animals are multicellular, heterotrophic eukaryotes with tissues that develop from embryonic layers.

3. How do animals differ from plants?

4. Animals lack cell walls and have have collagen as their most abundant protein. Animals have nerve and muscle cells. Animals have three distinct cell junc- tions: tight junctions, desmosomes, and gap junctions.

5. A Traditional View of Animal Diversity Based on Body-Plan Grades

6. Body Symmetry in Animals

7. Body Plans of the Bilateria

8. Early Embryonic Development

9. Animal Phylogeny Based on Sequencing of SSU-rRNA

10. Protostomes vs. Deuterostomes Indeterminate cleavage means the cells in the early divisions retain the capacity to develop into a complete embryo.

11. Sea Urchin Development From Single Cell to Larva

12. The Acrosomal and Cortical Reactions During Sea Urchin Fertilization

13. (d) Blastula. A single layer of cells surrounds a large blastocoel cavity. Although not visible here, the fertilization envelope is still present; the embryo will soon hatch from it and begin swimming. (b) Four-cell stage. Remnants of the mitotic spindle can be seen between the two cells that have just completed the second cleavage division. (c) Morula. After further cleavage divisions, the embryo is a multicellular ball that is still surrounded by the fertilization envelope. The blastocoel cavity has begun to form. • Cleavage partitions the cytoplasm of one large cell into many smaller cells called blastomeres (a) Fertilized egg. Shown here is the zygote shortly before the first cleavage division, surrounded by the fertilization envelope. The nucleus is visible in the center. Figure 47.7a–d

14. Fertilization in Mammals

15. Cleavage in an Echinoderm (sea urchin) Embryo

16. Cleavage in a Frog Embryo

17. Cross Section of a Frog Blastula

18. Gastrulation in a Frog Embryo

19. The three layers produced by gastrulation are called embryonic germ layers • The ectoderm forms the outer layer of the gastrula • The endoderm lines the embryonic digestive tract • The mesoderm partly fills the space between the endoderm and ectoderm

20. Eye Forebrain Neural tube Notochord Somite Heart Coelom Archenteron Endoderm Lateral fold Blood vessels Mesoderm Ectoderm Yolk stalk Somites YOLK Yolk sac Form extraembryonic membranes Neural tube Late organogenesis. Rudiments of most major organs have already formed in this chick embryo, which is about 56 hours old and about 2–3 mm long (LM). (b) Early organogenesis. The archenteron forms when lateral folds pinch the embryo away from the yolk. The embryo remains open to the yolk, attached by the yolk stalk, about midway along its length, as shown in this cross section. The notochord, neural tube, and somites subsequently form much as they do in the frog. (a) Figure 47.15a, b • Organogenesis in the chick is quite similar to that in the frog

21. ECTODERM MESODERM ENDODERM • Epithelial lining ofdigestive tract • Epithelial lining ofrespiratory system • Lining of urethra, urinarybladder, and reproductivesystem • Liver • Pancreas • Thymus • Thyroid and parathyroidglands • Epidermis of skin and itsderivatives (including sweatglands, hair follicles) • Epithelial lining of mouthand rectum • Sense receptors inepidermis • Cornea and lens of eye • Nervous system • Adrenal medulla • Tooth enamel • Epithelium or pineal andpituitary glands • Notochord • Skeletal system • Muscular system • Muscular layer of stomach, intestine, etc. • Excretory system • Circulatory and lymphaticsystems • Reproductive system(except germ cells) • Dermis of skin • Lining of body cavity • Adrenal cortex Figure 47.16 • Many different structures are derived from the three embryonic germ layers during organogenesis