Chapter 32

1. Chapter 32 An Introduction to Animal Diversity

2. Overview: Welcome to Your Kingdom • The animal kingdom: • Extends far beyond humans & other animals we may encounter • Living animals that have been identified: • 1.3 million living species Video: Coral Reef

3. Fig. 32-1

4. Animal are: • Animals are eukaryotes that are: • Multicellular • Heterotrophic • With tissues that developed from embryonic layers • Several characteristics, taken together, sufficiently define the group

5. Nutritional Mode, Cell Structure and Specialization • Animals are heterotrophs that ingest their food • They 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

6. Reproduction and Development • Most animals reproduce sexually • The diploid stage usually dominates the life cycle • After a sperm fertilizes an egg, the zygote undergoes rapid cell division called cleavage • Cleavage leads to formation of a blastula • The blastula undergoes gastrulation, forming a gastrula with different layers of embryonic tissues Video: Sea Urchin Embryonic Development

7. Fig. 32-2-3 Blastocoel Endoderm Cleavage Cleavage Blastula Ectoderm Archenteron Eight-cell stage Zygote Gastrulation Gastrula Blastocoel Blastopore Cross section of blastula

8. Many animals have at least one larval stage • A larva is: • Sexually immature, and • Morphologically distinct from the adult • It eventually undergoes metamorphosis

9. All animals, and only animals, have: • A family of genes called Hox genes • They regulate the development of body form • This Hox family of genes is highly conserved • Yet, it can produce a wide diversity of animal morphology

10. The history of animals spans more than half a billion years • The animal kingdom includes: • A great diversity of living species • An even greater diversity of extinct species • The common ancestor of living animals: • May have lived between 675 and 875 million years ago • May have resembled: • Modern choanoflagellates (protists that are the closest living relatives of animals)

11. Fig. 32-3 Single cell Stalk • Fossil Evidence of Animal Evolution from a Common Ancestor Over Four Geologic Era

12. Neoproterozoic Era (1 Billion–524 Million Years Ago) • Early members of the animal fossil record include: • The Ediacaran biota,which dates from 565 to 550 million years ago

13. Fig. 32-4 1.5 cm 0.4 cm (a) Mawsonites spriggi (b) Spriggina floundersi

14. Paleozoic Era (542–251 Million Years Ago) • The Cambrian explosion (535 to 525 million years ago): • Marks the earliest fossil appearance of many major groups of living animals • Several hypotheses explain the increase in diversity of animal phyla during the Cambrian explosion period: • New predator-prey relationships • A rise in atmospheric oxygen • The evolution of the Hox gene complex

15. Fig. 32-5

16. Mesozoic Era (251–65.5 Million Years Ago) • Coral reefs emerged, becoming important marine ecological niches for other organisms • Dinosaurs were the dominant terrestrial vertebrates during this era • The first mammals emerged

17. Cenozoic Era (65.5 Million Years Ago to the Present) • The Cenozoic era begins : • After mass extinctions of both terrestrial & marine animals • These extinctions included: • The large, non-flying dinosaurs • The marine reptiles • Modern mammal orders and insects diversified during the Cenozoic

18. Animals can be characterized by “body plans” • Zoologists sometimes categorize animals according to: • A body plan • A body plan is: • A set of morphological & developmental traits • A grade: • Is a group of animal species whose members share key biological features • It is not necessarily a clade, or monophyletic group

19. Symmetry • Animals can be categorized according to the symmetry of their bodies, or lack of it • Some animals have radial symmetry • Others have two-sided symmetry called bilateral symmetry • 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

20. Symmetry (a) Radial symmetry (b) Bilateral symmetry

21. 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 • During animal embryonic development: • Three germ layers give rise to the tissues & organs

22. Layers • Ectoderm: • Is the germ layer covering the embryo’s surface • Endoderm: • Is the innermost germ layer • It lines the developing digestive tube • The digestive tube is called the archenteron • Diploblastic: • Animals having ectoderm and endoderm • Triploblastic: • Animals with additional intervening mesoderm • Most possess a body cavity

23. Body Cavities • A true body cavity is: • Called a coelom • Derived from mesoderm • Coelomates: • Are animals that possess a true coelom

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

25. A pseudocoelom: • Is a body cavity derived from the mesoderm and endoderm • Pseudocoelomates: • Triploblastic animals that possess a pseudocoelom

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

27. (c) Acoelomate • Triploblastic animals that lack a body cavity are called acoelomates Body covering (from ectoderm) Tissue- filled region (from mesoderm) Wall of digestive cavity (from endoderm)

28. Protostome and Deuterostome Development • Based on early development, many animals can be categorized as having one of two developmental modes: • Protostome development, or • Deuterostome development

29. Cleavage • In protostome development: • Cleavage is spiral and determinate • In deuterostome development: • Cleavage is radial and indeterminate • With indeterminate cleavage: • Each cell in the early stages of cleavage retains the capacity to develop into a complete embryo • The production of identical twins becomes s

30. Fig. 32-9a (a) Cleavage Deuterostome development (examples: echinoderms, chordates) Protostome development (examples: molluscs, annelids) Eight-cell stage Eight-cell stage Spiral and determinate Radial and indeterminate

31. Coelom Formation • In protostome development: • The splitting of solid masses of mesoderm forms the coelom • In deuterostome development: • The mesoderm buds from the wall of the archenteron to form the coelom

32. Fig. 32-9b (b) Coelom formation Protostome development (examples: molluscs, annelids) Deuterostome development (examples: echinoderms, chordates) Coelom Key Ectoderm Archenteron Mesoderm Endoderm Coelom Blastopore Mesoderm Blastopore Mesoderm Solid masses of mesoderm split and form coelom. Folds of archenteron form coelom.

33. Fate of the Blastopore • The blastopore: • Forms during gastrulation • Connects the archenteron to the exterior of the gastrula • In protostome development: • The blastopore becomes the mouth • In deuterostome development: • The blastopore becomes the anus

34. Fig. 32-9c (c) Fate of the blastopore Protostome development (examples: molluscs, annelids) Deuterostome development (examples: echinoderms, chordates) Anus Mouth Key Ectoderm Digestive tube Mesoderm Endoderm Anus Mouth Mouth develops from blastopore. Anus develops from blastopore.

35. Fig. 32-9 Deuterostome development (examples: echinoderm, chordates) Protostome development (examples: molluscs, annelids) (a) Cleavage Eight-cell stage Eight-cell stage Radial and indeterminate Spiral and determinate (b) Coelom formation Key Coelom Ectoderm Mesoderm Archenteron Endoderm Coelom Blastopore Mesoderm Mesoderm Blastopore Solid masses of mesoderm split and form coelom. Folds of archenteron form coelom. (c) Fate of the blastopore Anus Mouth Digestive tube Mouth Anus Mouth develops from blastopore. Anus develops from blastopore.

36. New views of animal phylogeny is emerging from molecular data • Zoologists recognize about: • Three dozen animal phyla • Current debate in animal systematics has led to the development of: • Two phylogenetic hypotheses • But others exist as well

37. One hypothesis of animal phylogeny is based mainly on: • Morphological & developmental comparisons

38. Fig. 32-10 “Porifera” Cnidaria ANCESTRAL COLONIAL FLAGELLATE Metazoa Ctenophora Eumetazoa Ectoprocta Brachiopoda Deuterostomia Echinodermata Chordata Bilateria Platyhelminthes Rotifera Protostomia Mollusca Annelida Arthropoda Nematoda

39. Another hypothesis of animal phylogeny is based mainly on: • Molecular data

40. Fig. 32-11 Silicea “Porifera” Calcarea ANCESTRAL COLONIAL FLAGELLATE Metazoa Ctenophora Cnidaria Eumetazoa Acoela Echinodermata Deuterostomia Chordata Bilateria Platyhelminthes Rotifera Ectoprocta Lophotrochozoa Brachiopoda Mollusca Annelida Nematoda Ecdysozoa Arthropoda

41. Points of Agreement • All animals share a common ancestor • Sponges are basal animals • Eumetazoa is a clade of animals (eumetazoans) with true tissues • Most animal phyla belong to the clade Bilateria, and are called bilaterians • Chordates and some other phyla belong to the clade Deuterostomia

42. Disagreement over Bilaterian Relationships • The morphology-based tree divides bilaterians into two clades: • Deuterostomes • Protostomes • In contrast, recent molecular studies indicate three bilaterian clades: • Deuterostomia • Ecdysozoa, and • Lophotrochozoa • Ecdysozoans: • Shed their exoskeletons through a process called ecdysis

43. Fig. 32-12

44. Some lophotrochozoans have a feeding structure called a lophophore • Other phyla go through a distinct developmental stage called the trochophore larva

45. Fig. 32-13 Lophophore Apical tuft of cilia Mouth 100 µm Anus (a) An ectoproct (b) Structure of a trochophore larva

46. Future Directions in Animal Systematics • Phylogenetic studies based on larger databases will likely provide further insights into animal evolutionary history