I. Phyla.

    A. Platyhelminthes - Flatworms.
    B. Nematoda   - Roundworms.
    C. Annelida   - Segmented Worms.

II. General Characteristics of all Worms.

    A. Bilateral symmetry.
    B. Cephalization.
    C. Gas exchanged across body surface or at cell level.
    D. Body composed of three cell layers.

III.  Platyhelminthes.

    A. General Characteristics.
        1. True organs.
            a. Digestive.
            b. Sex.
            c. Neural.
        2. Mostly parasitic.

    B. Digestive and excretory functions.
        1. Only one opening.
        2. No circulatory system.
        3. Gut extends throughout body.

    C. Turbellaria.
        1. Small, free-living, inhabit freshwater.
        2. Ventral surface is ciliated.
        3. Light-sensing eyespots.
        4. Feed on smaller organisms or dead organic matter.
        5. Reproduction.
            a. Asexual: budding, transverse fission.
            b. Hermaphroditic, but never self-fertilize.
            c. Some parthenogenic (development from unfertilized eggs).

    D. Characteristics of parasitic flatworms.
        1. Few sense organs as adults.
        2. Thick tegument covers ths body to protect from digestive fluids.
        3. Suckers and/or hooks for attaching to a host.
        4. Absorb nutrients pre-digested directly from the host.
        5. Most of the body is devoted to reproductive organs.

    E. Flukes.
        1. Parasitic.
        2. 1 to few cm long.
        3. Suckers at anterior end and one on ventral surface.
        4. Suck host tissue or body fluids through a mouth.
        5. Simple digestive system.
        6. Most hermaphroditic.
        7. Serious health problem in undeveloped areas.
        8. Life cycle of the sheep liver fluke.
            a. Egg hatches from sheep feces.
            b. Ciliated larva.
            c. Enters a snail – intermediate host.
            d. Asexual reproduction.
            e. Emerges as tailed larvae.
            f. Form cyst on vegetation.
            g. Sheep eats the cyst.
            h. Fluke migrates to the liver.

    F. Tapeworms.
        1. Parasitic.
        2. No head, mouth, digestive system.
        3. Anterior end called scolex; has hooks and suckers.
        4. Attaches to lining of host’s intestine.
        5. Rest of the body is reproductive organs.
        6. Produces sections called proglottids by budding.
        7. Each proglottid has a complete set of reproductive organs.
        8. Proglottid full of fertilized eggs breaks off and passes out of host with feces.
        9. Life cycle of the pork tapeworm.
            a. Pig eats a proglottid.
            b. Eggs hatch in the intestine.
            c. Larvae migrate to muscle tissue and form cysts (bladderworms), each with a scolex.
            d. A person eats infected, poorly cooked pork, and the scolex attaches to the intestine.

IV. Nematoda.

    A. Fascinating Facts.
        1. The most abundant animals – 5 billion in top 3 inches of an acre of soil.
        2. 10,000 to 500,000 species estimated.
        3. Found in every environment – from hot springs to the arctic.
        4. Female can produce 200,000 eggs per day.

    B. General Characteristics.
        1. Very small – less than 1 inch.
        2. Digestive, reproductive, excretory, neural systems.
        3. No circulatory system.
        4. Nutrients diffuse through the fluid in the pseudocoelom.
        5. Cuticle covers outside of body.
        6. Many parasitic
            a. Damaging to humans in unsanitary conditions.
            b. Trichinella spiralis - trichinosis.
    C. Systems.
        1. Digestive: mouth, pharynx, intestine, anus.
        2. Reproductive: genital pore, vagina, uterus, ovary.
        3. Always reproduce sexually; separate sexes.

V. Annelida.

    A. General Characteristics.
        1. Metamerical segmentation, partitioned by septa.
        2. Closed circulatory system.
        3. Some blood vessels especially muscular, function as "hearts".
        4. Gas exchanged across body surface.
        5. Gills may enlarge surface area.

    B. Bristle worms.
        1. Mostly marine.
        2. Parapodia on each segment - fleshy paddle-like appendages.
        3. Setae - bristles on the parapodia; made of chitin.
        4. Separate sexes.

    C. Earthworms.
        1. Have setae (four pairs per segment), but no parapodia.
        2. Locomotion by planting the anterior setae, then pulling the posterior end forward.
        3. Ingest soil, extract organic matter, excrete inorganic material.
        4. Hermaphroditic.
        5. Australian earthworm 3 m long, 5 cm thick.
        6. Systems.
            a. Digestive: mouth, pharynx, esophagus, crop, gizzard, intestine, anus.
            b. Circulatory: dorsal blood vessel, ventral blood vessel, aortic arches.
            c. Excretory: nephridia filter waste from the blood and expel it.
            d. Nervous: “brain” is a pair of ganglia; double ventral nerve cord.
            e. Reproductive: testes, seminal vesicles; ovaries, oviducts.

    D. Leeches.
        1. Most ectoparasites; some predators or scavengers.
        2. .5 to 20 cm.
        3. Body often flattened.
        4. 34 segments.
        5. Sucker at each end of body.
        6. No circulatory system.
        7. Hermaphroditic.
        8. Mammalian parasites.
            a. "Teeth" to break through skin.
            b. Local anesthetic to keep host unaware.
            c. Anticoagulant.
            d. Quickly remove much blood - survive months between meals.

Lesson 17    Outline list    Lesson 19