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Chapter 26 The Higher Invertebrates Arthropods Annelids This table represents a comparison of the major invertebrate phyla and their important evolutionary developments. mouth coelom segmented body Mollusks anus head bilateral symmetry, cephalization false coelom complete digestive system mouth Roundworms Flatworms no coelom (no cavity between gut and body wall) unsegmented body Cnidarians, comb jellies radial symmetry, no cephalization saclike gut Sponges Success in Symmetry No symmetry, tissues or organs • Reproduce sexually and asexually. • Spicules • Osculum • Colar cells • Filter feeders Describe how a sponge goes through the process of filter feeding animation Cnidarians Radial symmetry Tissues Nematocysts 3 Classes Scyphozoans - Jellyfish Anthozoans - Sea anemones, corals Hydrozoans - Hydra mesogleafilled bell outer epithelium (epidermis) mesoglea inner epithelium (gastrodermis) outer epithelium mouth tentacle mouth Oral lobe (armlike extension of mouth) mesoglea inner epithelium Fig. 26.8, p. 428 mouth epidermis mesoglea tentacle interacting cells of nerve net gastrodermis sheet of epidermal cells with contractile properties Variations On the Cnidarian Body Plan Obelia Both polyp and medusa body forms Acoelomate Animals and the Simplest Organ Systems Simple and complex organs Organs One or more kinds of tissues, arranged in a particular pattern & proportions. Organ system When organs interacts with others; improves performance of a task. Flatworms Turbellarians, flukes, & tapeworms. Phylum - Platyhelminthes Flatworms Bilateral Cephalized Acoelomate Most are hermaphroditic 3 Classes Turbellarians (planarians) Trematodes (Flukes) Cestoda (Tapeworms) Organ Systems of a Planarian Class Turbullaria Nervous System Digestive System Reproductive System Flukes Trematoda Parasitic Sexual or asexual phases At least two hosts a. Mates in human host b. Leave host feces; hatch as ciliated larvae c. Ciliated larvae enter snail host d. Multiply asexually; exit forked larvae e. Swim and wait for human skin contact f. Borrow thru skin; migrate to intestine Life Cycle of Schistosoma japonicum Tapeworms Cestoda Parasitic Scolex Proglottids Hermaphroditic a. Inverted scolex larvae; muscle tissue b. Infected meat eaten c. Scolex emerges attaches to intestine d. Proglottids form e. Fertilized proglottids break off f. Cattle ingest eggs or proglottids Life cycle of Taenia saginata (beef tapeworm) Ribbon Worms – Nematoda Like flatworms Bilateral, acoelomate Ciliated surface Unlike flatworms Circulatory system Complete gut Separate sexes Roundworms Nematoda Pseudocoelomate Bilateral Cylindrical body Cuticle Complete digestive system Male and female Phylum - Rotifers Bilateral Cephalized Crown of cilia Pseudocoelomate Mostly fresh water Philodina roseola Two Early Developmental Modes of Animals Protostome & Deuterostome Differences: Cleavage Spiral (diagonal) Radial (parallel) Coelom formation Fate of blastopore Protostome, mouth develops first then anus Deuterostome, opposite digestive development Two Major Divergences Protostomes (lineage of coelomate) Mollusks, annelids, arthropods Spiral cleavage First embryonic opening --> mouth Coelom arises from spaces in mesoderm Deuterostomes Echinoderms, chordates Radial cleavage First embryonic opening --> anus Coelom arises from outpouchings in gut wall How a coelom forms in a protostome embryo: pouch will form mesoderm around coelom developing gut How a coelom forms in a deuterostome embryo: coelum solid mass of mesoderm developing gut In-text, p. 436 Slide 31 The Amazing Mollusks (Phylum Mollusca) A Sampling of Molluscan Diversity Mollusca Soft body Secrete Shell Mantle Tissue over visceral mass that secretes shell Fleshy foot Gills Important molluscan characteristics: Second largest group of invertebrates. Soft-bodied. Bilateral symmetry. Breathe through gills. Most species have: A head A “foot” A visceral mass Gut (complete) Heart Kidneys Reproductive organs Some have eyes & tentacles. Most have a shell or a remnant. Many have a radula for feeding. Mollusk Groups Gastropods Snails, slugs & nudibranchs Chitons “Univalves” Bivalves Clams, oysters, scallops & mussels Cephalopods Octopus, squid, cuttlefish, nautilus Largest group of mollusks. Crawl about on their “foot”. Many have coiled shells. Most show torsion – a twisting realignment of body parts. Secrete mucus to keep skin moist, reduce friction when crawling. Scrape food (mainly algae) off substrates by using a file-like radula. Often serve as intermediate hosts for parasitic worms. The Gastropods The Gastropods Torsion of the Viscera mouth anus gill Cilia near this region creates currents that sweeps waste away. excretory organ anus gill heart digestive gland mantle cavity (secretes the shell) stomach heart stomach shell radula mantle mouth radula (magnified) foot The Chitons Slow-moving or sedentary (sessile). Most use a radula to scrape algae off surfaces (like Gastropods). Have a large, broad muscular foot. Foot allows chitons to cling to surfaces tightly. Dorsal shell divided into eight plates. Mantle acts like suction cup, helping chiton stay attached to substrate. Include clams, oysters, scallops & mussels. Bivalve means “two shells”. Large foot specialized for burrowing. Gills used for respiration and trapping food particles. Water is drawn into mantle cavity through inhalant siphon, filtered through gills and expelled through exhalant siphon. Some bivalves (like scallops) can swim by clapping their valves together. The Bivalves retractor muscle retractor muscle mouth mantle gill water flows out through exhalant siphon palps water flows in through inhalant siphon foot shell Cilia on gills allow for suspension feeding by creating a movement of water through siphons The Cephalopods •Most highly developed brains of all invertebrates (eyes; learning & memory possible). •Beak-like crushing jaws. •Some have venomous bites. •Move swiftly via jet propulsion. •Only mollusks with closed digestive gland circulatory systems. esophagus stomach kidney brain internal shell arm jaw mantle reproductive organ radula ink sac gill siphon anus accessory heart (Speeds up circulation) heart tentacle Cephalopods have separate sexes! The Annelids (Phylum Annelida) Polychaetes tentacles eyes parapods Bodies divided into segments. Bilateral symmetry. Bristles on each body segment (except leeches). These can be retracted and provide traction for burrowing. Feed upon decomposing organic material. Thin cuticle allows gas exchange through skin. Two muscle types, circular & longitudinal. Complete digestive tract, closed circulatory system, brain & ventral nerve cord. Excretory nephridia. The Annelids (Phylum Annelida) Earthworm cross-section circular muscles dorsal blood vessel longitudinal muscles intestine coelom typhlosole Hydrostatic skeleton intestinal cavity seta (retracted) How do earthworms move? • circular muscles • longitudinal muscles • hydrostatic skeleton • setae cuticle ventral blood vessel nerve cord nephridium Regulates fluid balance Thin & flexible; permits gas exchange 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) Earthworm excretory system Earthworm circulatory system aortic arches (hearts) blood vessels (ventral and dorsal) Earthworm digestive system pharynx intestine mouth esophagus crop (storage) gizzard (mashing) Earthworm nervous system brain ganglion nerve cord Parasitic Annelids Before feeding After feeding Leeches are one of the few annelids without bristles. Have suckers at both ends of body to help with movement. Have razor-sharp jaws used to make incision in host’s skin. Secrete anticoagulant through mouth to prevent host’s blood from clotting. Gut has many side branches for storing victim’s blood. One feeding can last leech for one year. Like all annelids, leeches have segmented bodies. The Incredibly Diverse Arthropods (Phylum Arthropoda) Over 1 million different species, to date. Largest group of animals. New species discovered every week! Probably evolved from the annelids. Inhabit nearly every region of Earth. Four major lineages: Did you know that arthropods demonstrate the MOST diversity Trilobites (now extinct) Chelicerates (spiders, scorpions, ticks) Crustaceans (crabs, crayfish, shrimp) Uniramians (insects, centipedes, millipedes). Arthropod evolutionary success is due to six primary adaptations: A hardened exoskeleton. Specialized segments. Feeding Sensing Locomotion Sperm transfer Silk spinning Jointed appendages (only arthropods modified for flight) Specialized respiratory structures. Gills Tracheas (pores to tubes which allows for flight) Efficient nervous system & highly developed sensory organs (esp. site; compound eye) Division of labor in the life cycle. Types of Metamorphosis Growth and molting egg young egg nymphs adult Incomplete metamorphosis adult Complete metamorphosis egg larvae pupa adult The exoskeleton: a coat of armor! Made of chitin & protein, it’s light & flexible. Restricts water loss. Provides support & defense. Allows internal muscle attachment, enabling greater strength for organisms. Some disadvantages: Restricts size increases. Must be shed (molted) periodically (see at left). Restricts range of motion. Except for horseshoe crabs, all are terrestrial. Most are predators, some (ticks) are parasitic. Several pairs of simple eyes. Four pairs of walking legs. Chelicerae (fangs) in spiders used to inject venom. Pedipalps used for holding & tasting food. No antennae. Spiders produce silken webs. Book lungs for respiration. Scorpions- tip of abdomen modified into stinger with venom gland. The Chelicerates eyes digestive gland heart Malpighian tubule brain poison gland anus book lung pedipalp mouth sperm receptacle chelicera (fangs; inflict wounds & inject ovary silk gland spinners Ectoparasites of vertebrates. Feed on blood. Carry bacteria responsible for causing Rocky Mountain Spotted Fever and Lyme Disease (shown below). Ticks female male Shrimp, crayfish, crabs, The Crustaceans lobsters & pillbugs. 16 to 20 body segments. Head & thorax fused into a cephalothorax. Two pairs of antennae. Compound eyes on stalks. Three pairs of mouthparts. Five pairs of walking legs. First pair of walking legs modified into powerful chelipeds for defense. Gills used for respiration. antennae (two pairs) food-handling appendages (three pairs) one of two compound eyes fused segments of cephalothorax segments of abdomen swimmerets tail fin first leg (cheliped) five walking legs (five pairs total) External crayfish anatomy Note: 2 pairs of antennae; unique in arthropods Millipedes 4 legs per body segment. Cylindrical body shape. Feed on decaying plants. Secrete foul-smelling chemical for defense. Centipedes 2 legs per body segment. Flattened body shape. Fast, aggressive carnivores. Have fangs & venom glands. The Insects Body divided into head, thorax, abdomen (thorax adapted for locomotion) One pair of antennae. Locomotion: three pairs of walking legs, usually one pair of wings. Compound and simple eyes. Breathe through spiracles into tracheal tubes. Malpighian tubules remove nitrogen wastes from blood (conserves water) Nitrogen wastes combined with solid waste to conserve water. Only winged invertebrates. Aggressive competitors with man. Insect feeding adaptations Chewing (grasshopper) Sipping or Siphoning (butterfly) Sopping (housefly) Piercing & Sucking (mosquito) Arthropods, esp. insects, owe their evotionary success to … Hardened exoskeleton Specialized segments with joined appendages Efficient respiratory & sensory structures. Division of labor in their life cycles. Insect Life Cycles: Post Embryonic a. Growth and molting • Embryo • Nymph • Larvae egg young adult b. Incomplete metamorphosis • Pupae • Adult Note: egg nymphs adult c. Complete metamorphosis • Use different resources at different stages of development. • Winged; most successful • Only invertebrate with wings egg larvae adult • Check out the diversity of the appendages among the following insects. • How does this diversity help insects in term of feeding and food supply? The Puzzling Echinoderms (Phylum Echinodermata) Echinoderm means “spiny skinned” All contain calcium spines, spicules or plates in their body walls. Radial & bilateral symmetry. No brain, but nervous system present. Water vascular system with tube feet for locomotion. Swallow prey whole or push stomach out of body onto prey, partially digesting it before swallowing it. upper stomach anus gonad ossicle (stiffening, support structure) lower stomach coelom digestive gland eyespot the water-vascular system sieve plate or madreporeite ampulla ring canal tube feet Click to view water vascular system