1. Chapter 32 An Introduction to Animal Diversity

2. Overview: Welcome to Your Kingdom • The animal kingdom extends far beyond humans and other animals we may encounter Video: Coral Reef

4. 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

5. Nutritional Mode • Animals are heterotrophs that ingest their food

6. Cell Structure and Specialization • Animals are multicellular eukaryotes • Their cells lack cell walls

7. Their bodies are held together by structural proteins such as collagen • Nervous tissue and muscle tissue are unique to animals

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

9. 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 Video: Sea Urchin Embryonic Development

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

11. Many animals have at least one larval stage • A larva is sexually immature and morphologically distinct from the adult; it eventually undergoes metamorphosis

12. 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

13. 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

14. LE 32-3 Single cell Stalk

15. 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

16. Neoproterozoic Era (1 Billion–524 Million Years Ago) • Early members of the animal fossil record include the Ediacaran fauna

18. Paleozoic Era (542–251 Million Years Ago) • The Cambrian explosion marks the earliest fossil appearance of many major groups of living animals • There are several hypotheses regarding the cause of the Cambrian explosion

20. Mesozoic Era (251–65.5 Million Years Ago) • During the Mesozoic era, dinosaurs were the dominant terrestrial vertebrates • Coral reefs emerged, becoming important marine ecological niches for other organisms

21. 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 • Modern mammal orders and insects diversified during the Cenozoic

22. Concept 32.3: Animals can be characterized by “body plans” • Zoologists sometimes categorize animals according to morphology and development • A grade is a group of animal species with the same level of organizational complexity • A body plan is the set of traits defining a grade

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

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

25. LE 32-7a Radial symmetry

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

27. LE 32-7b Bilateral symmetry

28. 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

29. 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

30. 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

31. 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

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

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

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

35. Acoelomates are organisms without body cavities

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

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

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

39. 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

40. 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

41. 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

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

43. 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

44. Concept 32.4: Leading hypotheses agree on major features of the animal phylogenetic tree • Zoologists recognize about 35 animal phyla • Current debate in animal systematics has led to the development of two phylogenetic hypotheses, but others exist as well

45. One hypothesis of animal phylogeny based mainly on morphological and developmental comparisons

46. LE 32-10 Porifera Platyhelminthes Ctenophora Phoronida Brachiopoda Mollusca Arthropoda Cnidaria Echinodermata Chordata Annelida Ectoprocta Rotifera Nemertea Nematoda “Radiata” Deuterostomia Protostomia Bilateria Eumetazoa Metazoa Ancestral colonial flagellate

47. One hypothesis of animal phylogeny is based mainly on molecular data

48. LE 32-11 Ctenophora Platyhelminthes Mollusca Arthropoda Chordata Brachiopoda Phoronida Annelida Rotifera Echinodermata Ectoprocta Nemertea Nematoda Calcarea Cnidaria Silicarea “Radiata” Deuterostomia Lophotrochozoa Ecdysozoa “Porifera” Bilateria Eumetazoa Metazoa Ancestral colonial flagellate

49. Points of Agreement • All animals share a common ancestor • Sponges are basal animals • Eumetazoa is a clade of animals with true tissues • Most animal phyla belong to the clade Bilateria • Vertebrates and some other phyla belong to the clade Deuterostomia

50. Disagreement over the Bilaterians • The morphology-based tree divides bilaterians into two clades: deuterostomes and protostomes • In contrast, recent molecular studies assign two sister taxa to protostomes: the ecdysozoans and the lophotrochozoans