Animals What is an animal? Eukaryotic multicellular organisms Heterotrophs Digest food within body Can move (for what purposes?) No cell walls Development After fertilization, cell begins to divide Forms a hollow ball of cells called a blastula Cavity in blastula folds in to form a gastrula Structure made up of 2 layers of cells with an opening at one end Gastrulation Germ layers produces 2-3 germ layers (cell layers) each develops into specific structures ectoderm (outside) --> outer covering endoderm (inside) --> gut lining mesoderm (middle) --> muscles and other internal organs Germ Layers Adaptations Symmetry Body plans Protection & support Symmetry Balance in proportions Leads to different types of movement Asymmetry Irregular shape Ex. sponge Radial symmetry Can be divided in half along any plane Ex. hydra Bilateral symmetry Divided along its length into right & left halves Ex. humans Symmetry Body Plans Development of body cavities Only found in bilaterally symmetric animals Allowed for Larger growth Organ systems Types of Body Plans Acoelomate 3 body layers but no body cavity Organs embedded in solid tissues Do have a digestive tract Often flattened to allow for diffusion of nutrients, water, oxygen, & wastes Ex. flatworms Types of Body Plans (contd) Pseudocoelomates Body cavity between endoderm & mesoderm Pseudocoelom-fluid filled cavity partly lined with mesoderm Allows for quick movements Ex. roundworms Coelomates Coelom-fluid filled space completely surrounded by mesoderm Allows for development of specialized organs Ex. humans, insects, fishes Body Plans Protection & Support Exoskeletons Hard, waxy covering on outside of body Provides a framework for support Protect soft body tissue, prevent water loss, provide protection Secreted by epidermis Provide place for muscle attachment Exoskeleton Endoskeleton Internal skeleton that provides support inside an animals body Protects internal organs Internal brace for muscles Invertebrates Do not have a backbone Some have no skeleton Jellyfish, worms Often have exoskeletons Ex. crabs, spiders, grasshoppers, dragonflies, beetles Echinoderms are invertebrates but have endoskeleton Ex. starfish, sea biscuit, sand dollar Vertebrates Have a backbone All are bilaterally symmetric All have endoskeletons Ex. fish, birds, reptiles, amphibians, mammals