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ANIMAL KINGDOM MAIN CHARACTERISTICS • Multicellular, eukaryotic, heterotrophs • Specialized cells; most have tissues • Response to stimuli by nervous and muscular tissue • Most capable of locomotion; few sessile • Most diploid and reproduce sexually ANIMALS LIVE IN DIVERSE HABITATS • Marine • Origin of animal life • Provides buouyancy • Body fluids isotonic to environment • Plankton, nekton, sessile • Freshwater • Cells hypertonic to environment • Osmoregulation • More challenging than marine: food, oxygen, sunlight, temperature • Terrestrial – Threat of Dessication: • Body covering to reduce evaporation • Respiratory organs deep in body cavity • Reproduction • Eggs • Means of thermoregulation EVOLUTION OF ANIMALS • Common protist ancestor: choanoflagellate • Evo-Devo • Diversity • Hox genes CHARACTERISTICS USED TO FURTHER CLASSIFY ANIMALS… BODY SYMMETRY • Asymmetry • Radial symmetry • Bilateral symmetry CEPHALIZATION • Concentration of sensory structures in a head • Nerve cells concentrate in head brain • Nerve cord extends toward rear • Found in bilaterally symmetrical organisms • Adaptations to locomotion EMBRYONIC DEVELOPMENT • Zygote • Undergoes cleavage • Develops into blastula • Undergoes gastrulation 2 TYPES OF CLEAVAGE PATTERNS • Radial • Parallel or right angles to axis • Indeterminate • Spiral • Diagonal to axis • Determinate GERM LAYERS • Form in all animals except sponges DIPLOBLASTIC • 3 layers: • Ectoderm – outer layer • Endoderm – inner layer • Mesoderm – middle layer TRIPLOBLASTIC OVERVIEW OF ANIMAL TYPES • Sponges – loose arrangement of different types of cells; do not have tissues • Diploblastic • Cnidarians and Ctenophores • Only have 2 germ layers • Triploblastic • Have 3rd germ layer - mesoderm BODY CAVITY Triploblastic organisms further grouped base on presence and type of coelom – fluid-filled cavity between digestive tract and body wall BODY CAVITY CLASSIFICATION • Acoelomates • Solid body; no cavity • Flatworms and ribbon worms • Pseudocoelomates • Have a body cavity but it is not completely lined with mesoderm • Nematodes and rotifers • Coelomates • Tube-within-a-tube body plan • Coelom completely lined with mesoderm • Comparison 2 MAIN GROUPS OF BILATERAL ANIMALS: • During gastrulation, group of cells move in forming sac … embryonic gut • If blastopore becomes mouth – organism is a protostome • If blastopores becomes anus deuterostome PROTOSTOMES VS. DEUTEROSTOMES PROTOSTOMES DEUTEROSTOMES • Flatworms, annelids, arthropods, mollusks • Echinoderms and chordates • Spiral, determinant cleavage • Radial, indeterminate cleavage • Schizocoely • Enterocoely Fig. 29-7, p. 627
