Introduction to Invertebrates Chapter 29

Introduction to Invertebrates 2Outline Evolution of Animals Multicellularity  Sponges True Tissues  Cnidarians and Comb Jellies ­Hydra ­Obelia Bilateral Symmetry  Flatworms  Roundworms Body Cavities  Acoelomates  Psuedocoelomates  Eucoelomates

Introduction to Invertebrates 3 Evolution of Animals All animals are multicellular heterotrophic organisms that must take in preformed food Classification Criteria  Level of organization ­Cellular, tissue, organ  Body Plan ­Sac, tube-within-a-tube  Segmentation ­Segmentation leads to specialization

Introduction to Invertebrates 4 Evolution of Animals Classification Criteria, cont  Symmetry ­Radial - Two identical halves ­Bilateral - Definite right and left halves  Type of Coelom ­Pseudocoelom ­Coelom  Early Developmental Pattern ­Protostome - First embryonic opening becomes the mouth ­Dueterostome - Second embryonic opening becomes the mouth

5 Traditional Phylogenetic Tree of Animals

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Introduction to Invertebrates Evolution of the Animal Body Plan 1.Animal body plans generally become increasingly complex, from asymmetrical, to radial, to bilateral. 2.Body plans are determined by the pattern of genes being expressed or not expressed, at different times and regions of the developing embryo. 3.In the first stages of development, the anterior and posterior ends of the embryo are defined. 4.In animals that have bilateral symmetry and segments, the next step in development is diving the embryo into segments. 7

Introduction to Invertebrates Evolution of the Animal Body Plan 5After the segmentation pattern is established, the Hox (homeotic) genes determine what each segment will be. a.Hox genes bind to the genetic area that determines the body plan during development. b.Each Hox gene determines the developmental fate of a particular region of the body. 1)In mice, Hox C8 determines that 12 segments become the thoracic vertebrate. 2)In snakes, Hox C8 determines the development of hundreds of thoracic vertebrae. c.Hox genes are found in all animals and there is a shared similarity among animal groups. d.Hox genes have evolved from a common ancestor. 8

9 Simple Sponge Anatomy

Introduction to Invertebrates 10 True Tissue Layers Total of three possible germ layers  Ectoderm  Endoderm, and  Mesoderm phlya Ctenophora and Cnidaria develop only ectoderm and endoderm  Diploblasts  Radially symmetrical

11 Comb Jelly Compared to Cnidarian

12 Cnidarian Diversity

13 Anatomy of Hydra

14 Obelia Life Cycle

15 Ribbon Worm, Lineus

16 Planarian Anatomy

17 Parasitic Flatworms - Schistosomiasis

18 Parasitic Flatworm – Tapeworm,Taenia

Introduction to Invertebrates 19PseudocoelomPseudocoelom:  A “false” body cavity that is incompletely lined by mesoderm  Provides a space for internal organs and can serve as hydrostatic skeleton Roundworms (phylum Nematoda)  Non-segmented, generally colorless worms  Several parasitic roundworms infect humans

20 Roundworm Anatomy

21 Filarial Worm

22 Rotifer

Introduction to Invertebrates Ending Slide Chapter 29