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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) 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 Body Organization • Cephalization – Sensory cells concentrated at the head • Segmentation – Repetition of body units, front-to-back Body Cavities • Most bilateral animals have a coelom and a complete gut 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 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. Unique Cnidarian Weapons • Nematocysts – Used to capture prey and for defense Flatworms (Phylum Platyhelminthes) • Free-living turbellarians (planarians), parasitic tapeworms and flukes – Simplest animals with organ systems – Bilateral protostomes – Paired nerve cords, ganglia – Hermaphrodites 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 Mollusks (Phylum Mollusca) • Soft body with mantle. • Including gastropods (snails), bivalves (scallops), chitons, nudibranchs, cephalopods – 100,000 named species 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 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