I. Mollusca.

    A. General Structure.
        1. Bilateral symmetry.
        2. The ventral aspect is comprised of a muscular foot, used for locomotion and gripping rocks.
        3. The visceral hump contains the internal organs: heart, digestive, excretory.
        4. The dorsal aspect is covered by a mantle.
            a. A thickened fold of tissue that covers the visceral hump and sometimes overhangs it.
            b. Secretes the shell.
        5. The mantle cavity is a space between the mantle and the visceral hump.
        6. A shell often covers the mantle.
            a. Protection.
            b. Anchors the muscles.
        7. The head contains the sensory organs, brain, and mouth.

    B. Body systems.
        1. Digestive.
            a. Radula, mouth, stomach, intestine, anus.
            b. The radula, a small organ like a tongue made of sandpaper, scrapes up food particles and draws them into the mouth.
        2. Circulatory.
            a. True heart.
            b. Closed vessels that pass through the gills or lungs.
            c. An open, blood-filled cavity that bathes the internal tissues.
        3. Excretory: nephridia.
        4. Respiratory: gills or lungs hang down in the mantle cavity.
        5. Neural.
        6. Reproductive: many have a larval stage.

    C. Bivalvia.
        1. Oysters, clams, mussels, scallops.
        2. Most are marine, some freshwater.
        3. Two-part hinged shell (each half called a valve).
        4. Most are ciliary filter feeders.
            a. Lack a radula.
            b. Circulate water through two siphons.
            c. Food is trapped in a stringy, sticky mucus.
            d. Cilia move the food and mucus mixture into the mouth.
        5. Most are sedentary.
    D. Gastropoda.
        1. Snails, slugs, limpets, nudibranches.
        2. Marine, freshwater, terrestrial.
        3. Foot located immediately below the visceral hump, where the stomach is.
        4. Locomotion by gliding over a thin layer of slime.
        5. Graze on plant material.
        6. Shell (if present) is spiral coil or flattened cone.
        7. Anus empties on top of head.
        8. Some have a "lung" in the mantle cavity.

    E. Cephalopoda.
        1. Octopuses, squid, nautiluses, cuttlefish.
        2. Shells.
            a. Nautiluses have external shells.
            b. Squid have a rod-like internal cuttlebone made of calcified chitin.
            c. Octopuses have no shell of any sort.
        3. Foot extends from the head region.
        4. Foot is usually divided into 8 to 10 sucker-bearing tentacles.
        5. Carnivorous.
        6. Closed circulatory system.
        7. Internal fertilization.
        8. Octopuses and squid.
            a. Large, complex eyes.
            b. Highly developed brain.
            c. Can swim by jet propulsion.
            d. Squid can reach 60 feet long.

    F. Amphineura.
        1. Chitons.
        2. Marine.
        3. Oval, with 8 lateral plates.
        4. Shallow water and intertidal areas.
        5. Feed on algae.
        6. External fertilization.

II. Echinodermata.

    A. General Characteristics.
        1. Means "spiny skinned."
        2. CaCO3 spines and plates under the skin.
        3. Relatively sedentary.
        4. Most begin as ciliated, bilaterally symmetrical larvae.
        5. Radial symmetry in adults.
        6. No head or excretory system.
        7. The central disk contains the mouth, stomach, and anus.
        8. Water vascular system with tube feet.
        9. All are marine.
        10. Separate sexes, external fertilization.
        11. Can regenerate if a portion of the central disk is present.

    B. Water vascular system.
        1. A modified portion of the coelom that acts as a hydraulic device.
        2. A ring canal circles the central disk.
        3. Radial canals extend to each arm.
        4. Opens to the sea at the sieve plate on the dorsal side of the central disk.
        5. In sea stars, tube feet protrude from the radial canals along their length.
        6. The tube feet have suckers on their ventral end, and ampullae at the opposite end.
        7. The ampullae can contract, forcing water into the foot and causing it to extend.
        8. Coordination of the suckers, ampullae, and muscles enable locomotion.
        9. Can withstand the force of the surf, and can pry open mollusk shells.

    C. Other Systems.
        1. Eat by everting their stomach and secreting digestive enzymes into the prey.
        2. The resulting soupy broth is transported throughout a highly branched digestive glands for digestion to be completed.
        3. Respiration occurs directly between the coelom and the environment.
        4. Skin gills are extensions of the animal surface that aid in respiration and excretion.
        5. Amebocytes move through the coelom gathering waste, then exit the animal through the skin gills.

    D. Asteroidea - sea stars.
        1. Flat, with central disk.
        2. Most are carnivorous.
        3. Eat mollusks.
        4. Regenerate whole body from part of one arm plus central disk.

    E. Echinoidea - sea urchins, sand dollars.
        1. Brittle calcareous spines.
        2. CaCO3 plates fused into solid sphere or envelope with openings for mouth, anus, feet.
        3. Tube feet used for gas exchange.
        4. Lack arms.
        5. Scavengers.

    F. Ophiuroidea - brittle stars, serpent stars.
        1. Similar appearance to Asteroidea, but disk more distinct, arms thinner and tentacle-like.
        2. Many are covered with spines.
        3. Most eat organic detritus and small organisms.
        4. Readily discard their arms when attacked or disturbed.

    G. Holothuroidea - sea cucumbers.
        1. Look like large flabby sausages.
        2. Skeleton reduced to microscopic plates.
        3. Lack arms.
        4. Lie on side, with mouth at end.
        5. Trap organic material on their sticky, feathery tentacles.
        6. Shed their internal organs when attacked, then regenerate them.