2. CH 24 WHAT IS AN ANIMAL?

3. CHARACTERISTICS OF ALL ANIMALS Eukaryotic Multicellular Specialized cells (tissues & organs) Ingestive heterotrophs 1.5 million species

4. STRUCTURES FOR SUPPORT AND DEVELOPMENT Exoskeletons – - hard or tough outer coverings - provide a framework for support - protect soft body tissues - prevent water loss - protection against predators Found on many invertebrates

5. Invertebrates – animals without backbones - 95-99% of animal species - most have an exoskeleton - exoskeletons are shed to make a new one as the animal grows - Some invertebrates, sea urchins and sea stars; have internal skeletons (endoskeletons)

6. Invertebrates Examples – animals without backbones - Sponges, Cnidarians – first animals to evolve from a multicellular ancestor - Worms: flatworms, roundworms, segmented worms - Mollusks: octopus, snails, squids, clams - Arthropods: crustaceans, spiders, insects - Echinoderms: sea stars, sea urchins, sand dollars - Invertebrate Chordates: lancelet, tunicates

7. Vertebrates – animals with a backbone Endoskeleton – internal skeletons grow with the animal - calcium carbonate -sea urchins/sea stars (invertebrates) - cartilage – sharks - bone – fishes, amphibians, reptiles, birds, mammals

8. SEXUAL REPRODUCTION (MOST)  Sperm + Egg = Zygote  Cleavage - - > zygote divides  Embryo -> an organism in the early stages of development

9. CELL LAYERS (Most have three layers)  Ectoderm - outer layer (skin & nervous tissue)  Endoderm - inner layer (digestive organs)  Mesoderm – middle layer (muscles, circulatory, excretory and respiratory systems)

10. SYMMETRY  Radial - round, or sphere shaped  Bilateral – right and left halves form a mirror image  Asymmetrical – no definite shape

11. BODY PLANES  Dorsal - back surface  Ventral - belly surface  Anterior - top (head)  Posterior - tail end

12. BODY CAVITIES Coelum - fluid-filled cavity - mesoderm (earthworms) Acoelomate - no body cavity (flatworms)