1. The Invertebrates Animals are multicelled heterotrophs that move about for at least part of their life cycle Animals develop in a series of stages –Ectoderm, endoderm, and often mesoderm form in the early embryo –Cells interact in functional units (epithelium and connective tissues)

2. Comparing Key Groups Evolutionary trends toward –Greater size –Compartmentalization (division of labor among cells, tissues, and organs) –Integration of specialized activities that keep the organism alive Most animals are bilateral –Mouth –anus

3. Body Organization Cephalization –Sensory cells concentrated at the head Segmentation –Repetition of body units, front-to-back

4. Body Cavities Most bilateral animals have a coelom and a complete gut

5. Sponges (Phylum Porifera) Sponges –No symmetry, tissues, or organs –Flattened cells line the body wall (many pores; spikes of silica and/or proteins) –Skeleton of silicon, calcium, or spongin (protein fibers) –Filter feeders (flagellated collar cells absorb food; amoeboid cells digest and distribute it) –Hermaphrodites –Zygote develops into free-living larva

6. Cnidarians (Phylum Cnidaria) Jellyfishes, corals, and sea anemones –Radial, tentacled carnivores (bag like with only one opening –Gastrovascular cavity (respiration and digestion) –True epithelial tissues with a jellylike matrix in between (mesoglea) –Simple nervous system (nerve net) –Hydrostatic skeleton –Some are commercial, some symbiotic with algae Eaten by molluscs and flatworms for nematodes. Base of food web.

7. Unique Cnidarian Weapons Nematocysts –Used to capture prey and for defense

8. Flatworms (Phylum Platyhelminthes) Free-living turbellarians (planarians), parasitic tapeworms and flukes –Simplest animals with organ systems –Bilateral protostomes –Paired nerve cords, ganglia –Hermaphrodites

9. Annelids Segmented worms (earthworms, polychaetes) and leeches –Closed circulatory system –Digestive and excretory systems, solute-regulating nephridia –Nervous system, ganglia in each segment –Muscles and fluid in chambers act as a hydrostatic skeleton –Hermaphrodites

10. Mollusks (Phylum Mollusca) Soft body with mantle. Including gastropods (snails), bivalves (scallops), chitons, nudibranchs, cephalopods –100,000 named species

11. Cephalopods Another class of molluscs. The fastest (squids), largest (giant squids), and smartest (octopuses) invertebrates Have a mantle –Sheetlike part of the body mass, draped back on itself

12. Echinoderms Sea stars, sea urchins, sea cucumbers, etc. –Invertebrates of the deuterostome lineage –Exoskeleton with spines, spicules, or plates of calcium carbonate –Water-vascular system with tube feet –Adults are radial, but bilateral traits appear in larval stages and other features