Architectural Pattern of an Animal

1. Architectural Pattern of an Animal Chapter 9

2. The Appearance of Major Body Plans • The Cambrian explosion marks the earliest fossil appearance of all major groups of living animals plus some groups that are only known from fossils. • All major body plans appeared at this time. • Result of extensive selection. • Are limiting determinant of future adaptational variants.

3. Body Plans • One way in which zoologists categorize the diversity of animals is according to general features of morphology and development. • A group of animal species that share the same level of organizational complexity is known as a grade.

4. Hierarchical Organization – 5 Levels • Protoplasmic grade of organization – protists are the simplest eukaryotes, but they still carry out life functions and show division of labor among the various cell structures. • Metazoans are multicellular animals that have cells specialized for particular functions. This is the Cellular grade of organization. • Shown by the simplest metazoans – Volvox, sponges.

5. Hierarchical Organization – 5 Levels • Cell-tissue Grade – Usually, specialized cells are grouped together and perform their common function as a coordinated unit, a tissue. • Jellyfish • Tissue-organ Grade – Tissues are then assembled into organs like the heart (primarily muscle tissue, but connective, nervous, and epithelial also present). • Flatworms

6. Hierarchical Organization – 5 Levels • Organ-system grade – In the highest level of organization, organs work together as organ systems like the circulatory system.

7. Animal Body Plans • Body plans are constrained by ancestry, major features may become modified, but are rarely lost. • Animal body plans differ in their grade of organization, body symmetry, number of germ layers, and type of body cavity.

8. Symmetry • Spherical symmetry occurs when anyplane passing through the center divides the body into mirror image halves. • Mostly found among the protists.

9. Symmetry • Radial symmetry applies when more than two planes passing through the longitudinal axis can divide the organism into mirror image halves. • Jellyfish • Biradial symmetry – two planes will divide the organism. • Comb jellies

10. Radiata • The Cnidarians (jellyfish, corals & sea anemones) and Ctenophores (comb jellies), the radial or biradial animals, comprise the Radiata. • No front/back • Weak swimmers • Can interact with environment in all directions.

11. Symmetry • Bilateral symmetry is found in organisms where one plane can pass through the organism dividing it into right and left halves. • Better for directional movement. • Monophyletic group called Bilateria.

12. Cephalization • Bilateral symmetry is associated with cephalization, differentiation of a head. • Nervous tissue, sense organs, and often the mouth are located in the head. • Advantages for organisms moving head first – directional movement. • Elongation along anteroposterior axis.

13. Regions of a Bilaterally Symmetrical Animal • Anterior-posterior (transverse plane) • Dorsal-ventral (frontal plane) • Left-right (sagittal plane) • Proximal-distal • Medial-lateral

14. Body Cavities • Examples of body cavities include the gut, blastocoel, and a pseudocoel or coelom. • The gut forms from the archenteron during gastrulation. • The blastocoel persists in some, but usually fills with mesoderm. • Pseudocoel and coelom are fluid filled body cavities that cushion organs and provide support.

15. Body Cavities • In protostomes, mesoderm forms as endodermal cells from near the blastopore migrate into the blastocoel. • Three body plans possible: • Acoelomate (no body cavity) • Pseudocoelomate (body cavity between endoderm & mesoderm) • Coelomate (body cavity surrounded by mesoderm)

16. Body Cavities • Coeloms surrounded by mesoderm can arise in two ways: • Schizocoely – mesodermal cells fill the blastocoel, forming a solid band of tissue around the gut, then a space opens inside the mesodermal band. • Enterocoely – portions of the gut lining form pockets that pinch off and form a ring of mesoderm.

17. Developmental Patterns • Sponges develop only to blastula stage, then reorganize to form adult. • Gastrulation allows animals to proceed to tissue level organization. • Diploblastic – 2 germ layers • Cnidarians, Ctenophores • Triploblastic – 3 germ layers

18. Other Key Features of Body Plans • In some organisms, the gut does not form a complete tube. • Waste must come back out the mouth. • Food must be digested & waste expelled before eating again. • A complete gut forms a tube within a tube body plan.

19. Other Key Features of Body Plans • Segmentation is a serial repetition of similar body segments along the body. • Each segment is a metamere or somite. • May include external & internal components. • Obscured in many animals, like humans. • Permits greater body mobility and complexity of structure & function.

20. Components of Metazoan Bodies • Extracellular Components - noncellular components of metazoan animals: • Body fluids • Extracellular structural elements

21. Tissue Structure and Function • A tissue is a group of similar cells specialized for performing a common function. • Different types of tissues have different structures that are suited to their functions. • Tissues are classified into four main categories: • Epithelial • Connective • Muscle • Nervous • Cellular Components - Tissues

22. Epithelial Tissue • Epithelial tissue covers the outside of the body and lines organs and cavities within the body. • Squamous, cuboidal, columnar. • Simple vs. stratified.

23. Connective Tissue • Connective tissue functions mainly to bind and support other tissues. • Contains sparsely packed cells scattered throughout an extracellular matrix.

24. Muscle Tissue • Muscle tissue is composed of long cells called muscle fibers capable of contracting in response to nerve signals. • Smooth • Skeletal • Cardiac

25. Nervous Tissue • Nervous tissue senses stimuli and transmits signals throughout the animal. • A neuron (nerve cell) receive signals at the dendrites and send them out via the axons.

26. Complexity and Body Size • Increased complexity allows for an increase in body size. • Larger size decreases the surface area to volume ratio. • Necessitates complex systems for respiration, nutrition, and excretion – diffusion not adequate. • Buffers environmental fluctuation. • Escape predators.

27. Complexity and Body Size • 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.