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Invertebrates Invertebrates Nearly all animals are invertebrates (95%) Invertebrates are animals that lack backbones Let’s take a survey of the major phyla of animals! Chordates Echinoderms Major Animal Phyla Arthropods Annelids Coelomate Ancestry Mollusks Rotifers Roundworms Bilateral Ancestry Radial Ancestry Multicelled Ancestry Figure 25.2 Page 415 Flatworms Cnidarians Sponges Single-celled, protistanlike ancestors Symmetry Radial Bilateral Figure 25.3 Page 416 The Gut Region where food is digested and then absorbed Saclike gut One opening for taking in food and expelling waste Complete digestive system Opening at both ends; mouth and anus Body Cavities - Acoelomate epidermis gut cavity no body cavity; region between gut and body wall packed with organs Figure 25.4a Page 417 Body Cavities - Pseudocoel epidermis gut cavity unlined body cavity (pseudocoel) around gut Figure 25.4b Page 417 Body Cavities - Coelom gut cavity lined body cavity (coelom) peritoneum Figure 25.4c Page 417 Segmentation Repeating series of body units Units may or may not be similar to one another Earthworms - segments appear similar Insects - segments may be fused and/or have specialized functions Animal Origins Originated during the Precambrian (1.2 billion - 670 million years ago) From what? Two hypotheses: Multinucleated ciliate became compartmentalized Cells in a colonial flagellate became specialized Phylum Porifera Representative organism: sponge Have no true tissues (Parazoa) Sponges are sessile (nonmotile) Ancient Greeks believed them to be plants Filter-feeders: Their cells are relatively unspecialized Trap food from the water that flows through them Most sponges are hermaphrodites Each individual produces both sperm and eggs Sponge Structure water out glasslike structural elements amoeboid cell pore semifluid matrix central cavity flattened surface cells water in Figure 25.7a flagellum microvilli nucleus Page 419 Phylum Cnidaria Have stinging cells inside of nematocysts On tentacles capsule’s lid at free surface of epidermal cell trigger barbed thread inside capsule nematocyst Figure 25.8 Page 420 Phylum Cnidaria Representative Organisms: Jellyfish & Sea Anemones Have true tissues and radial symmetry Body plan: sac with a central digestive compartment known as the gastrovascular cavity (mouth & anus) 2 variations on the body plan: Polyp: sessile, mouth up, waits for prey (sea anemone) Medusa: floats, mouth down (jellyfish) Attack prey with tentacles 33-06b-JellySwimming-B.mov Two Main Body Plans outer epithelium (epidermis) mesoglea (matrix) Medusa Figure 25.9 Page 420 inner epithelium (gastrodermis) Polyp Obelia Life Cycle (Hydrozoan) reproductive polyp male medusa female medusa ovum sperm zygote feeding polyp polyp forming planula Figure 25.10 Page 421 Phylum Platyhelminthes Representative Organisms: Bilateral symmetry Acoelomates – Tapeworms, flukes, & planarians no body cavity enclosed by mesoderm Many are parasitic Planarian Organ Systems flame cell nucleus pharynx cilia protonephridia opening of tubule at body surface flame cell fluid filters through membrane folds Fig. 25.11a,b Page 422 Planarian Organ Systems brain nerve cord ovary testis oviduct genital pore penis Fig. 25.11cd Page 422 Flukes: Class Trematoda Parasitic worms Complicated life cycle Larval stage infects a mollusk Adult infects a Worms mate in human host Larvae bore into human skin Larvae form, leave snail Fertilized egg Asexual reproduction in intermediate host Ciliated larva vertebrate Southeast Asian blood fluke Figure 25.14 Page 424 Tapeworms: Class Cestoda Definitive host Larvae encysted in muscle tissue Intermediate host Scolex attaches to host intestinal wall Figure 25.15 Mature proglottid with fertilized eggs Page 424 Phylum Nematoda Representative organism: roundworms Pseudocoelomate have a body cavity, but not encased by mesoderm Round worms with tapered ends Can be parasitic (trichinosis) Roundworms (Nematoda) pharynx False coelom (pseudocoelomate) Complete digestive system intestine false coelom eggs in uterus gonad anus muscularized body wall Figure 25.13 Page 423 Two Coelomate Lineages Protostomes Deuterostomes Mollusks Echinoderms Annelids Chordates Arthropods Cleavage Patterns Protostome embryo (spiral cleavage) Blastopore becomes mouth Deuterostome embryo (radial cleavage) Blastopore becomes anus In-text figure Page 426 Phylum Mollusca Representative organisms: Coelomates snails, slugs, oysters, clams, octopuses, squids Have a true coelom Protostomes: Blastopore becomes mouth Phylum Mollusca Body plan has 3 main parts: Muscular foot used for movement Visceral mass covering the internal organs Mantle covers the visceral mass (may produce a protective shell) Cuttlefish Body Plan Closed circulatory system with heart and accessory heart esophagus digestive kidney stomach gland Figure 25.22 Page 429 brain arm jaw tentacle mantle reproductive internal siphon ink sac heart accessory organ shell radula anus gill heart Phylum Annelida Representative Organism: earthworm Annelids have segmented bodies Metanephridia (similar to kidneys) Worms are hermaphrodites Remove wastes from the blood Produce both sperm and eggs Setae provide traction for burrowing in the soil Earthworms eat their way through the soil 33-23-EarthwormLocomot-B.mov