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Animals: The Invertebrates Chapter 25 Characteristics of Animals • Multicelled heterotrophic eukaryotes • Require oxygen for aerobic respiration • Reproduce sexually, and perhaps asexually • Motile at some stage • Develop from embryos Chordates Major Animal Phyla Echinoderms 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 Placozoa • One living species, Tricoplax adherens • Simplest known animal • Two-layer body, 3 mm across Figure 25.5 Page 418 Sponges - Phylum Porifera • No symmetry • No tissues • No organs • Reproduce sexually • Microscopic swimming larval stage 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 • Only animals that produce nematocysts • Nerve net • Hydrostatic skeleton • Saclike gut capsule’s lid at free surface of epidermal cell trigger barbed thread inside capsule nematocyst Figure 25.8 Page 420 Cnidarian Diversity • Scyphozoans – Jellyfish • Anthozoans – Sea anemones – Corals • Hydrozoans 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 Flatworms: Phylum Platyhelminthes • Acoelomate, bilateral, cephalized animals • All have simple or complex organ systems • Most are hermaphrodites Three Classes • Turbellarians (Turbellaria) • Flukes (Trematoda) • Tapeworms (Cestoda) 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 Roundworms (Nematoda) • False coelom • Complete digestive system pharynx intestine false coelom eggs in uterus gonad anus muscularized body wall Figure 25.13 Page 423 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 Rotifers • Bilateral • Cephalized • False coelom • Crown of cilia at head end • Complete gut Figure 25.17 Page 425 Two Coelomate Lineages Protostomes • Mollusks • Annelids • Arthropods Deuterostomes • Echinoderms • Chordates Cleavage Patterns Protostome embryo (spiral cleavage) Deuterostome embryo (radial cleavage) In-text figure Page 426 Mollusks: Phylum Mollusca • Bilateral, soft-bodied, coelomate • Most have a shell or reduced version of one • Mantle drapes over body and secretes shell • Most have a fleshy foot • Many have a radula for shredding food Molluscan Diversity • Gastropods • Chitins • Bivalves • Cephalopods Torsion • Twisting of body parts during larval development • Occurs only in gastropods mouth gill anus Figure 25.18 Page 426 Body Plan of a Snail heart mantle cavity anus gill mantle digestive gland foot radula Figure 25.18 Page 426 Body Plan of a Clam mouth left mantle retractor muscle retractor muscle foot palps left gill shell Figure 25.21 Page 429 Cephalopods • Only the nautilus retains external shell • Other cephalopods are streamlined, active swimmers • All move by jet propulsion – Water is forced out of mantle cavity through a funnel-shaped siphon • Have large brains relative to body size 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 Annelids: Phylum Annelida Segmented, coelomate worms • Class Polychaeta • Class Oligochaeta • Class Hirudinea Polychaetes • Most are marine • Bristles extend from paired, fleshy parapods on each segment • Head end is specialized “jaws” toothlike structures pharynx (everted) antenna palp (food handling) tentacle eyes chemicalsensing pit parapod Fig. 25.24c Page 430 Leeches - Class Hirudinea • Predators and parasites • Less obvious body segmentation • Most have sharp jaws Earthworm - An Oligochaete No parapodia, few bristles per segment Dorsal blood vessel Circular muscle Coelom Longitudinal muscle Nephridium Nerve cord Figure 25.25a Page 431 Seta (retracted) Nerve cord Earthworm Nephridium bladderlike storage region of nephridium nephridium’s thin loop reabsorbs some solutes, relinquishes them to blood blood vessels body wall funnel (coelomic fluid with waste enters here) external pore (fluid containing wastes discharged here) Figure 25.25b Page 431 Earthworm Circulatory System Hearts Figure 25.25c Page 431 Earthworm Digestive System Coelomic chambers Esophagus Crop Gizzard Pharynx Mouth Figure 25.25d Page 431 Earthworm Nervous System Brain Nerve cord Figure 25.25e Page 431 Arthropods: Phylum Arthropoda • The phylum with the greatest number of species • Four lineages: – Trilobites (all extinct) – Chelicerates (spiders, mites, scorpions) – Crustaceans (crabs, shrimps, barnacles) – Uniramians (insects, centipedes, millipedes) Adaptations for Success • Hardened exoskeleton • Jointed appendages • Fused and modified segments • Respiratory structures • Specialized sensory structures • Division of labor Do not post on Internet Figure 25.26 Page 432 Chelicerates • Originated in seas • A few are still marine: horseshoe crabs, sea spiders • The arachnids are all terrestrial Spiders Mites Scorpions Chiggers “Daddy longlegs” Ticks Body Plan of a Spider eye brain heart digestive gland Malpighian tubule poison gland book lung ovary silk gland pedipalp mouth sperm receptacle anus spinners chelicera Figure 25.28 Crustaceans • Most are marine, some freshwater, a few terrestrial • Head has two pairs of antenna, three pairs of food-handling appendages Copepods Crayfish Barnacles Lobsters Shrimps Crabs Isopods (pillbugs) Lobster Body Plan one of two eyes antennae (two pairs) fused segments of cephalothorax segments of abdomen food-handling appendages (three pairs) swimmerets tail fin first leg five walking legs (five pairs total) Figure 25.29a Page 434 Crab Life Cycle Larval and juvenile stages molt repeatedly and grow in size egg Figure 25.30 Page 435 Millipedes and Centipedes • Segmented bodies with many legs • Millipedes – Two pairs of legs per “segment” – Scavengers • Centipedes – Flattened, with one pair of legs per segment – Predators Insect Body Plan • Thorax usually has three pairs of legs and one or two pairs of wings • Abdomen contains most internal organs and specialized structure for reproduction • Three-part gut • Malpighian tubules attach to midgut and serve in elimination of wastes Insect Headparts Butterfly Mosquito Grasshopper antenna labrum mandible Fly maxilla palps labium Figure 25.32 Page 436 Insect Diversity • The only winged invertebrates • More than 800,000 known species • Most successful species are small in size and have a great reproductive capacity Types of Insect Development Growth and molting egg young adult Incomplete metamorphosis Different stages exploit different resources at different times egg adult nymphs Complete metamorphosis egg larvae pupa adult Unwelcome Arthropods • Poisonous spiders • Disease-carrying ticks • Venomous scorpions • Agricultural pests Do not post on Internet Corn rootworm (Diabrotica virgifera) Figure 25.38 Page 439 Echinoderms • Deuterostomes • Body wall has spines or Do not post photos on Internet plates • No brain • Adults are radial with Sea urchin bilateral features Sea cucumber Figure 25.39 Brittle star Page 440 Echinoderm Diversity • Crinoids (sea lilies and feather stars) • Sea stars • Brittle stars • Sea urchins, heart urchins, sand dollars • Sea cucumbers Body Plan of a Sea Star sieve plate gonad coelom anus upper stomach lower stomach digestive gland eyespot Figure 25.40a Page 441 Water Vascular System sieve plate ampulla Figure 25.40b Page 441