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Fundamentals of Biology

Lesson 20

Arthropods


I. Phyla.

    A. Crustacea: lobsters, crabs, shrimp, crayfish.
    B. Arachnida: spiders, scorpions, ticks, mites.
    C. Insecta.
    D. Diplopoda: millipedes.
    E. Chilopoda: centipedes.

II. General Characteristics.

    A. "Jointed foot".
    B. Body segmentation.
    C. Exoskeleton of cuticle.
        1. Mostly made of chitin.
        2. Also contains glycoproteins, waxes, lipids that seal body fluids in and keep water out.
        3. Thin and flexible at joints.
        4. Molting during growth.
    D. Bundles of muscles attached to inside of cuticle on either side of joints.
    E. Open circulatory system with dorsal heart.
        1. Hemocoel: body cavity
        2. Filled with a clear hemolymph fluid that bathes most internal tissues.
    F. Ventral nervous system.
    G. Separation of sexes.
    H. Internal fertilization in terrestrial species; external fertilization in aquatic species.
    I. Regeneration as a means of repair.

III. Crustacea.

    A. General Characteristics.
        1. Most aquatic; some terrestrial, some parasitic.
        2. Some are filter feeders, using setae for filters.
        3. Cuticle impregnated with CaCO3 – makes it hard.
        4. Tiny species prominent in plankton.

    B. Body Structure.
        1. Two part division.
            a. Cephalothorax.
                i. Two pairs antennae.
                ii. Three pairs for feeding.
                iii. Appendages for walking: five in the common species.
            b. Abdomen.
        2. Respiration by gills.

    C. Crayfish.

IV. Arachnida.

    A. Body Structure.
        1. Two part division.
            a. Cephalothorax.
                i. No antennae or mandibles.
                ii. One pair of chelicerae: contain poisonous fangs.
                iii. One pair of pedipalps.
                    a) Sense and hold food while eating.
                    b) In male, transfer sperm.
                iv. Four pairs of legs.
            b. Abdomen.
        2. Respiration.
            a. Book lungs.
            b. Some have tracheae.

    B. Spiders.
        1. All spin silk with spinnerets.
        2. Silk is a fine, elastic protein.
        3. Silk produced as liquid, but hardens in air.
        4. All are carnivorous.
        5. Usually poison their prey.

V. Insecta.

    A. Fascinating Facts.
        1. 300 million individuals for every person.
        2. 900,000 species.
        3. Most terrestrial, some freshwater.

    B. Body Structure.
        1. Three part division.
            a. Head.
                i. One pair antennae.
                ii. Compound eyes.
                iii. Mouth.
            b. Thorax.
                i. Three pairs legs.
                ii. Zero, one, or two pairs wings.
            c. Abdomen.
        2. Mouth Types.
            a. Sponging (fly).
            b. Siphoning (butterfly).
            c. Piercing (mosquito).
            d. Chewing (grasshopper, most others).
                i. Labrum: upper lip.
                ii. Mandibles (pair) for chewing.
                iii. Maxillae (pair) for feeding.
                iv. Maxillary palps for feeding.
                v. Labium: lower lip.
                vi. Labial palps: fastened to the labium.
        3. Wing Types.
            a. Membranous: thin. transparent, with supporting veins (most insects).
            b. Scale-covered: delicate, colored scales (butterfly, moth).
            c. Leather-like: protective (grasshopper).
            d. Horny: protective (beetle).
        4. Digestive System.
            a. Mouth
            b. Salivary glands.
            c. Foregut.
                i. Esophagus.
                ii. Crop.
                iii. Gizzard.
            d. Midgut.
                i. Stomach.
                ii. Gastric ceca provide digestive juices.
                iii. Major site of digestion and absorption.
            e. Hindgut.
                i. Intestine.
                ii. Rectum.
                iii. Anus.
        5. Respiration.
            a. Spiracles: pores that admit air.
            b. Tracheae: finely branched tubes throughout body.
        6. Excretory System.
            a. Malpighian tubules: thin ring of tubules encircling junction of stomach and intestine.
            b. They extract nitrogenous wastes from the blood and empty into the intestine for elimination.
        7. Neural System.
            a. Sense of smell usually centered in the antennae.
            b. Taste receptors on the mouthparts.
            c. Tactile hairs over the body enable sense of touch.
            d. Compound eyes.
            e. Some have hearing organs.
        8. Reproduction.
            a. Male deposits sperm into the seminal receptacle.
            b. Ovipositor lays the eggs.
            c. Eggs are fertilized as they are laid.

    D. Type of development.
        1. Egg - Immature - Adult.
            a. Immature is a small version of adult.
            b. Silverfish.
        2. Egg - Nymph - Adult.
            a. Nymph is wingless version of adult.
            b. Grasshoppers, crickets, termites, aphids.
        3. Egg - Naiad - Adult.
            a. Naiad is aquatic version, with gills.
            b. Mayflies, dragonflies.
        4. Egg - Larva - Pupa - Adult (90% of cases).
            a. Larva is totally different from adult.
            b. Pupa is the immobile stage in which metamorphosis occurs.
            c. Metamorphosis: body structures and organs of the larva are dismantled and reshaped.
            d. Butterflies, beetles, flies, bees, ants.

    E. Major orders.
        1. Hymenoptera (bees, wasps, ants).
            a. “Membrane-winged.”
            b. Many are social.
            c. Only stinging insects.
        2. Lepidoptera (butterflies, moths).
        3. Coleoptera (beetles).
            a. Largest order of insects: 250,000 species.
            b. Exoskeleton of some can support over 1,500 times their own weight.
        4. Diptera (flies, mosquitoes, gnats).
        5. Orthoptera (grasshoppers, cockroaches).

VI. Chilopoda (centipedes).
    A. “Thousand-foot.”
    B. Carnivore.
    C. Flattened body.
    D. Many-segmented body with one pair of legs per segment.
    E. Amazing speed and agility.
    F. Some tropical centipedes can reach 1 ft. and capture worms and snakes.

VII. Diplopoda (millipedes).
    A. “Double-foot.”
    B. Herbivore and scavenger.
    C. Rounded body.
    D. Two pairs of legs per segment.
    E. Moves slowly.

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