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Chapter 32

Chapter 32. An Introduction to Animal Diversity. 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

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Chapter 32

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  1. Chapter 32 An Introduction to Animal Diversity

  2. 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

  3. Nutritional Mode • Animals are heterotrophs that ingest their food • 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 to animals

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

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

  6. 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

  7. 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

  8. LE 32-3 Single cell Stalk

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

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

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

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

  13. 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

  14. 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

  15. 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

  16. 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

  17. LE 32-8a Coelom Body covering (from ectoderm) Tissue layer lining coelom and suspending internal organs (from mesoderm) Digestive tract (from endoderm) Coelomate

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

  19. LE 32-8b Body covering (from ectoderm) Muscle layer (from mesoderm) Pseudocoelom Digestive tract (from endoderm) Pseudocoelomate

  20. Acoelomates are organisms without body cavities

  21. LE 32-8c Body covering (from ectoderm) Tissue- filled region (from mesoderm) Wall of digestive cavity (from endoderm) Acoelomate

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

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

  24. 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

  25. 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

  26. LE 32-9b Deuterostome development (examples: echinoderms, chordates) Protostome development (examples: molluscs, annnelids, arthropods) Coelom formation Coelom Archenteron Coelom Blastopore Mesoderm Mesoderm Blastopore Schizocoelous: solid masses of mesoderm split and form coelom Enterocoelous: folds of archenteron form coelom

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

  28. LE 32-9c Deuterostome development (examples: echinoderms, chordates) Protostome development (examples: molluscs, annnelids, arthropods) Fate of the blastopore Mouth Anus Digestive tube Mouth Anus Mouth develops from blastopore Anus develops from blastopore

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