Chapter 18- Evolution of Animal Diversity Animals- multicellular, heterotrophic eukaryotes that obtain nutrients by ingestion First animals- – Probably evolved from protists that lived as colonies of cells – Eventually cells in colony specialized – Evolved into 2 groups: Invertebrates (no backbone) and Vertebrates (backbone) Invertebrate Animals – 1. Sponges- (Porifera) Among simplest animals Many radially symmetrical Filter water through porous body to obtain food – 2. Cnidarians- (Cnidaria) Simplest animal with tissues Radially symmetical 2 forms: – Polyp- hydra and coral – Medusas- jelly fish Tentacles (with cnidocytes) capture prey Tentacles (controlled by nerves) push prey through mouth into gastrovascular cavity Only 1 opening in digestive tract Only 2 layers in body

Body style- most animals (except cnidarians) are bilaterally symmetrical – Surfaces: anterior and posterior (head/tail), dorsal and ventral (top/bottom), lateral (sides) – 3. Flatworms (Platyhelminthes) Flukes and tapeworms Simplest bilaterally symmetrical animals Simple nervous system- brain, sense organs, nerve cord, branching nerves One opening digestive tract Body cavity – Fluid filled space between digestive tract and body wall – Sponges, cnidarians and flatworms lack cavity but nearly all other animals have body cavity – Pseudocoelom (false coelom)- body cavity not completely lined by tissue derived from mesoderm – Coelom- body cavity completely lined by tissue derived from mesoderm Soft bodies- fluid in coelom acts as hydroskeleton Skeletons- fluid acts as cushion when moving – 4. Roundworms (Nematoda) Nematodes Pseudocoelom 2 opening digestive system- mouth and anus

– 5. Mollusks (Mollusca) Gastropods- snails, slugs Bivalves- clams, scallops Cephalopods- octopi, squid Muscular foot and mantle- which may secrete shell Many feed with radula- scrapes food looks like chainsaw Coelom Circulatory system Segmentation- subdivision of body parts along its length into series of repeated parts- allows for great movement – 6. Annelids (Annelida) Earthworms, sandworms, leeches Segmented bodies Live in moist conditions Leeches used for medical reasons (remove blood, relieve swelling, anticoagulant) – 7. Arthropods (Arthropoda) Horseshoe crabs, lobster, insects, spiders Segmented bodies Has exoskeleton and jointed appendages Molt to grow Insects- largest, most successful phylum ever

– Echinoderms (Echinodermata) Sea star, sea urchins Marine animals Spiny skin and exoskeleton Radially symmetrical as adults Suction cup like feet function in respiration and locomotion – Chordates (Chordata) Segmented body 4 features in embryos and sometimes in adults: 1- dorsal hollow nerve cord 2- stiff notochord (longitudinal rod between digestive tract and nerve cord) 3- pharyngeal slits behind mouth 4- Muscular post anal tail 2 groups: 1- invertebrates- lack backbone – tunicates, lancelets 2- vertebrates- skull and backbone made in series of vertebrae – Ex: fish, birds, amphibian, reptile, mammal (see chart on next page) Phylogenetic tree gives animal diversity an evolutionary perspective – Traditional tree- depends on comparative anatomy and embryology – Molecular tree- depends on similar nuceoltide sequences in RNA **non-native species threatens diversity