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1 CHAPTER 9 Architectural Pattern of an Animal New Designs for Living Zoologists recognize 34 major phyla of living multicellular animals Survivors of around 100 phyla that appeared 600 million years ago during Cambrian explosion Most important evolutionary event in geological history of life Virtually all major body plans were established Major body plans Result of extensive selection Are limiting determinant of future adaptational variants Hierarchical Organization of Animal Complexity Grades of Organization Unicellular protozoans Simplest eukaryotic organisms Protoplasmic Grade of Organization Perform all basic functions with confines of single cell Hierarchical Organization of Animal Complexity Hierarchical Organization of Animal Complexity Metazoa Multicellular animals Cells are specialized parts of whole organism Cannot live alone Cellular Grade of Organization Simplest metazoans Cells demonstrate division of labor but are not strongly associated to perform a specific collective function Tissue Grade of Organization Cells grouped together Perform common function as a unit (tissue) Tissue Tissue Organ Grade of Organization (Eumetazoans) Tissues assembled into larger functional units called organs Chief functional cells of organ Parenchyma Supportive tissues Stroma

2 Hierarchical Organization of Animal Complexity Organ System Grade of Organization Organs work together to perform a common function Highest level of organization Associated with most animal phyla Animal Symmetry Symmetry Correspondence of size and shape of parts on opposite sides of a median plane Spherical symmetry Any plane passing through center divides body into mirrored halves Best suited for floating and rolling Found chiefly among some unicellular forms Rare in animals Radial symmetry Body divided into similar halves by more than 2 planes passing through longitudinal axis Biradial symmetry Variant form radial symmetry Have part that is single or paired rather than radial Only 2 planes passing through longitudinal axis produces mirrored halves Usually sessile, freely floating, or weakly swimming animals No anterior or posterior end Can interact with environment in all directions Bilateral Symmetry Organism can be divided along a sagittal plane into two mirror portions Right and left halves Much better fitted for directional (forward) movement Associated with cephalization Differentiation of a head region with concentration of nervous tissue and sense organs Advantageous to an animal moving through its environment head first Always accompanied by differentiation along an anteroposterior axis

3 Regions of bilaterally symmetrical animals Anterior Head end Posterior Tail end Dorsal Back side Ventral Front or belly side Medial Midline of body Lateral Sides Distal Parts farther from the middle of body Proximal Parts are nearer the middle of body Frontal plane (coronal plane) Divides bilateral body into dorsal and ventral halves Sagittal plane Divides body into right and left halves Transverse plane (cross section) Divides body into anterior and posterior portions Body cavity Sponges Acoelomate: no body cavity In sponges After blastula formation, cells reorganize to form adult body Blastula has no external opening No gut forms Other animal phyla Development proceeds from blastula to gastrula Invagination of surface cells form the archenteron or primitive gut Opening to archenteron is the blastocoel Becomes the mouth or the anus Gut is lined by endoderm Outer layer of cells is ectoderm Embryo now has 2 cavities Gut and blastocoel Blastocoel persists in some animals In others, becomes filled with a 3 rd germ layer, mesoderm Cells forming mesoderm Derived from endoderm 22 mechanisms of formation In Protostomes Mesoderm forms as endodermal cells near blastopore migrate into the blastocoel Three body plans are possible Acoelomate plan Mesodermal cells completely fill the blastocoel Gut is only body cavity

4 Pseudocoelomate plan Mesodermal cells line the outer edge of the blastocoel 22 body cavities formed Persistent blastocoel (pseudocoelom pseudocoelom) and a gut cavity Pseudocoelom is a false body cavity (only partially lined with mesoderm) Schizocoelous plan Mesodermal cells fill blastocoel Mesoderm splits The space is called a coelom True body cavity (completely lined by mesoderm) 22 body cavities formed Gut and coelom In Deuterostomes Mesoderm forms by an enterocoelous plan Cells from central gut lining form pouches Pouches expand into blastocoel Wall forms mesodermal ring Pouches enclose a space, coleom Pouches pinch off from gut lining Coelom completely fills blastocoel 2 body cavities form Gut and coelom Developmental Origins in Triploblasts Body Plans Triploblastic animals follow one of several major developmental pathways Most common pathways are by spiral or radial cleavage Radial cleavage Typically accompanied by 3 traits Blastopore becomes the anus and new opening becomes the mouth Coelom formation is by enterocoely Cleavage is regulative Animals with these features called deuterostomes

5 Developmental Origins in Triploblasts Body Plans Developmental Origins in Triploblasts Body Plans Spiral cleavage Produces embryos whose developmental pattern contrast with those of deuterostomes Blastopore becomes the mouth Cleavage is mosaic Mesoderm forms from 4d cell May be acoelomate, pseudocoelomate, or coelomate (schizocoely) Animals with these features are called lophotrochozoan protostomes Ecdysozoan protostomes Exhibit a range of cleavage patterns including spiral cleavage Coelomate or psuedocoelomate A Complete Gut Design and Segmentation Few diploblasts and triploblasts form blind gut Same opening for entrance of food and exit of wastes Most form a complete gut Allows for one way flow of food from mouth to anus Tube within within a tube tube design A Complete Gut Design and Segmentation Metamerism (Segmentation) Serial repetition of similar body segments along longitudinal axis of body Each segment is a metamere or somite Permits greater body mobility and complexity of structure and function Annelids, Arthropods, Chordates

6 Extracellular Components Noncellular components of metazoan animals Body fluids Extracellular structural elements Cellular Components: Tissues Histology is the study of types of tissues Four major types of tissues form during embryonic development Epithelial Tissue Connective Tissue Muscular Tissue Nervous Tissue Epithelial Tissue Sheet of cells that covers an internal or external surface Avascular Function Protection Absorption Secretion Simple epithelia Single layer of cells Found in all metazoa Stratified epithelia 22 or more cell layers Restricted to vertebrates Separated from underlying tissues by a basement membrane

7 Connective Tissue Widespread in body Contains relatively few cells, many fibers, and a ground substance or matrix 2 types of connective tissue proper In vertebrates Loose connective tissue Contains fibers and both fixed and wandering cells in a viscous fluid matrix Dense connective tissues Characterized by densely packed fibers and little matrix Connective tissue also includes blood, lymph, cartilage, and bone Muscular Tissue Most abundant tissue in most animals Originates from mesoderm Muscle cell called a muscle fiber Specialized for contraction 3 types Skeletal Striated, unbranched, multinuclei, and voluntary Cardiac Striated, branched, 1 2 nuclei, involuntary Smooth No striations, unbranched, 1 nucleus, involuntary Nervous Tissue Specialized to receive stimuli and conduct impulses from one region to another 2 basic cell types Neurons Structural and functional unit of nervous system Neuroglia Insulate and support neurons

8 Complexity and Body Size More complex grades of metazoan organization Permit and promote evolution of large body size As body increases in size Surface area area to to volume ratios have important consequences for animal respiration, heat, etc. Surface area increases as the square of body length Volume increases as the cube of body length Complexity and Body Size Complexity and Body Size A large animal has less surface area compared to its volume than does a smaller animal May be inadequate for respiration and nutrition by cells located deep within its body Flattening or infolding the body increases surface area, as in flatworms Most animals developed internal transports systems to shuttle nutrients, gases and waste products, as they became larger Cope s Law of Phyletic Increase Lineages began with small individuals and eventually evolved toward giant forms Large forms frequently became extinct Provided opportunities for new lineages, which in turn evolve larger forms Holds for many nonflying vertebrate and invertebrate groups Complexity and Body Size Benefits of Being Large Buffers against environmental fluctuations Provides protection against predators and promotes offensive tactics Cost of maintaining body temperature is less per gram of body weight than in small animals Energy costs of moving a gram of body weight over a given distance less for larger animals

9 Geologic Time Scale