Lecture Overview

1. Lecture Overview Introduction to the Animals The Simplest Animals The Advent of Bilateral Symmetry The Advent of a Body Cavity Redesigning the Embryo

2. General Features of Animals All animals are multicellular heterotrophs They all require oxygen for respiration Animals are diverse in form There are ~ 10 million living species ~ 99% are invertebrates (lacking a backbone) ~ 1% are vertebrates (possessing a backbone) There are about 36 phyla Most occur in the sea Three phyla dominate life on land Arthropoda; Mollusca; Chordata

3. Animals lack cell walls They are usually quite flexible Animals are mobile They move more rapidly and in more complex ways than members of other kingdoms Most animals reproduce sexually An animal develops from a zygote by a characteristic process of embryonic development Morula ? Blastula ? Gastrula Details vary widely between phyla Provide clues to evolutionary relatedness

4. The Animal Family Tree Taxonomists have traditionally created phylogenies (family trees) based on two main criteria Anatomical features Embryonic development

5. The second branch: Symmetry Eumetazoa have two branches Radiata Have radial symmetry

7. Puzzling minor groups do not fit well into the standard either-or organization A New Look at the Animal Family Tree

8. Molecular systematics uses unique sequences within certain genes to identify clusters of related groups The animal phylogenetic tree is viewed as a hierarchy of clades nested within larger clades Using DNA/RNA/protein data, a variety of molecular phylogenies have been produced in the last decade They all have the same deep branch structure as the traditional animal family tree However, most agree on a revolutionary difference The protostomes are broken into two distinct clades

9. There are three prominent hypotheses for the origin of metazoans from single-celled protists 1. The multinucleate hypothesis The ancestor was a multinuclear protist like today�s ciliates 2. The colonial flagellate hypothesis The ancestor was a colonial protist Hollow spherical colony of flagellated cells 3. The polyphyletic origin hypothesis Sponges evolved independently of eumetazoans Molecular evidence clearly favors hypothesis #2 �Evo-Devo� and Roots of the Animal Family Tree

10. Nearly all the major animal body plans can be seen in Cambrian rocks dating from 543-525 mya However, the branches of the animal family tree arose in the earlier Ediacaran era Biologists have long debated what caused this Cambrian explosion of animal diversity Proposed reasons include Emergence of predatory lifestyles Geological factors, such as the buildup of minerals in the oceans �Evo-Devo� and Roots of the Animal Family Tree

11. A third possibility for the Cambrian explosion comes from the new field of �evo-devo� �Evo-Devo� and Roots of the Animal Family Tree

12. Sponges: AnimalsWithout Tissues The Kingdom Animalia consists of two subkingdoms Parazoa Animals that lack symmetry and possess neither tissues nor organs 1 phylum: Porifera Eumetazoa Animals that have symmetry and in most cases tissues and organs About 35 phyla

13. Sponges are the simplest animals Bodies consist of little more than masses of specialized cells embedded in a gel-like matrix The adult sponge is shaped like a vase It is anchored in place on the seafloor

14. Sponges are perforated by tiny holes Basis of the Phylum name Porifera Unique flagellated cells called choanocytes or collar cells, line the body cavity of the sponge Beating of the flagella draws water in through the pores and drives it through the cavity The sponge is a �filter-feeder� The choanocytes of sponges very closely resemble a kind of protist called choanoflagellates These may be the ancestors of all animals

17. Cnidarians: Tissues Lead to Greater Specialization The structure of eumetazoans is much more complex than that of sponges Radially symmetric eumetazoans form two distinct embryonic layers An outer ectoderm ? epidermis An inner endoderm ? gastrodermis A jelly-like layer called the mesoglea forms between the epidermis and gastrodermis

18. There are two radially symmetric phyla Together, they are called Radiata 1. Cnidaria

19. Carnivores that capture their prey with tentacles Bear unique stinging cells called cnidocytes Contain a small but powerful harpoon called a nematocyst A major evolutionary innovation among the radiates is extracellular digestion of food In radiates, digestion begins in the gastrovascular cavity Cnidarians

21. Cnidarians have two basic body forms

23. Solid Worms: Bilateral Symmetry Radiates are radially symmetrical Have a regular arrangement of parts around a central axis

24. Bilaterally symmetrical animals have evolved a definite head end, a process called cephalization Solid worms are the simplest of all bilaterally symmetrical animals

25. Members of Platyhelminthes The largest phylum of solid worms Simplest animals in which organs occur Some species are free-living Most species are parasitic Tapeworms Flukes Flatworms

28. Have incomplete gut with only one opening Cannot eat, digest and excrete food simultaneously Have an excretory system consisting of a network of tubules running throughout the body Have a simple nervous system Lack a circulatory system Most are hermaphroditic Flatworms

29. Roundworms: The Evolutionof a Body Cavity The evolution of an internal body cavity was important for three reasons Circulation Rapid passage of material Movement Muscle-driven body movement Organ function Little deformation by surrounding muscles

30. Three kinds of body plans

31. There are seven phyla The pseudocoel serves as a hydrostatic skeleton Gains rigidity from being filled with fluid under pressure Therefore muscles can work against this �skeleton� Lack a defined circulatory system Two important phyla Roundworms: Pseudocoelomates

32. Nematodes are bilaterally symmetrical, cylindrical, unsegmented worms Covered by a thick, flexible cuticle Mouth is equipped with piercing organs called stylets Food passes through the mouth by the sucking action of the pharynx Lack flagella or cilia Reproduction is sexual Phylum Nematoda

34. Caenorhabritis elegans Only animal whose complete cellular anatomy is known Trichinella sp. Cause trichinosis Acquired from pigs Ascaris lumbricoides Intestinal roundworm Infects one out of every six people worldwide Phylum Nematoda

35. Mollusks: Coelomates The bulk of the animal kingdom consists of coelomates Development of specialized tissues in animals involves primary induction In this process one of the three primary tissues interacts with another A major advantage of the coelomate body plan is that it allows mesoderm�endoderm contact

36. Only major phylum of coelomates without a segmented body The second largest animal phylum, after Arthropods The body consists of three distinct parts Head-foot; Visceral mass; Mantle Gills capture O2 from water and release CO2 The radula is a rasping, tongue-like organ Used to scrape algae off rocks Mollusks

37. The three major groups of mollusks

39. Characteristics of Animals Multicellular Heterotrophs Lack Cell Walls Mobile Sexual Reproduction

40. Characterization of Animals Phylogenies based on: Anatomical Features Embryological Development

41. Generalized Animal Phylogeny

42. Annelids: The Riseof Segmentation Segmentation is the building of a body from a series of similar segments It offers evolutionary flexibility Small change in existing segment can produce a new segment with a different function The first segmented animals to evolve were the annelid worms, phylum Annelida

43. Most annelid species are marine About one-third are terrestrial Representative annelids

44. The basic body plan is a tube within a tube Three characteristics Repeated segments Separate segments able to expand or contract independently Specialized segments Front segments contain the worm�s sensory organs Connections Materials and information pass through partitions in the segments Segmentation underlies the body organization of all complex coelomate animals

46. Arthropods: Advent ofJointed Appendages Arthropods belong to the phylum Arthropoda The most successful of all animal groups

47. All arthropods have jointed appendages They have a rigid external skeleton made up of chitin This exoskeleton protects the animals and provides sites for muscle attachment It is brittle, so its thickness limits arthropod body size

49. Arthropods that lack jaws, or mandibles Their mouthparts, called chelicerae, are the foremost appendages of the body Mandibulates are arthropods that have mandibles Chelicerates

50. Arachnida is the largest class of chelicerates 57,000 named species Largely terrestrial organisms Spiders, ticks, mites, scorpions Chelicerates

51. Crustaceans Mandibulates

52. Crustaceans Mandibulates

53. Millipedes and Centipedes Mandibulates

54. Insects Mandibulates

55. Insects Mandibulates

56. Protostomes andDeuterostomes In the coelomates there are two different developmental patterns In protostomes, the mouth develops from or near the blastopore The anus (if present) develops later from another region of the embryo In deuterostomes, the anus develops from or near the blastopore The mouth develops later from another region of the embryo

59. Deuterostomes differ from protostomes in three other fundamental embryological features

60. Echinoderms:The First Deuterostomes Echinoderms have an endoskeleton composed of hard calcium-rich ossicles that are often fused They consist of about 6,000 living marine species

61. Echinoderms are bilaterally symmetrical as larvae But they become radially symmetrical as adults This could be an environmental adaptation Adults have a five-part body plan The key evolutionary innovation is the development of a water vascular system A fluid-filled system with a central ring canal and five radial canals Thousands of tiny, hollow tube feet extend from each radial canal

63. Chordates:Improving the Skeleton Chordates are members of the phylum Chordata

64. Distinguishing features of chordates

66. Vertebrates