Biology.

Biology

Chapter 22 Worms and Mollusks I. Flatworms and Roundworms
A. Structural Characteristics 1. Bilateral Symmetry – equal left and right halves. a. Anterior – front b. Posterior – back c. Ventral – lower d. Dorsal – upper 2. Ganglia – clusters of nerve cells that form a simple brain. a. Normally on anterior end of organism 3. Coelom – body cavity

II. Platyhelminthes – phylum of flatworms
A. Are acoelomates – do not have a body cavity. B. Class: Turbellaria 1. Planaria – are free living organisms a. Most are aquatic and less than 1 cm in length b. Round anterior, pointed posterior c. Has a muscular pharynx to suck in food 1) Located in the middle, ventral part of the body d. Undigested food is excreted back through the mouth. e. Eyespots – contain pigmented cells and detect light changes f. Ganglion on anterior end

g. Reproduce both sexually and asexually.
1) hermaphrodite – contain both male and female reproductive organs. 2) Have to cross-fertilize with other planaria. 3) Are capable of regeneration C. Class: Cestoda 1. Tapeworm – flat ribbon-like body and may grow up to 12m in length. a. Have hooks and suckers to attach to the host. b. Lack sense organs and digestive tract. 1) Nutrients are absorbed through the body. c. Live in the intestines of the host. d. Scolex – knob shaped head

e. Proglottids – body sections produced behind the head.
1) Each contain male and female reproductive organs 2) Produce 100’s of thousands of eggs and will break off and pass out of the organism with the feces. f. Life Cycle – Taenia saginatum (beef tapeworm) 1) Cow eats eggs and proglottids 2) Larvae hatch in stomach, burrow through walls, and travel to muscles to form cysts. 3) Humans eat poorly cooked meat and cyst dissolves in stomach 4) Adult tapeworm attaches to the intestine and “feeds”

D. Class: Trematoda 1. Fluke – usually only 1 cm long a. Have suckers, hooks, and tough body coverings. b. Most are hermaphrodites c. Most have life cycles that include 2 to 4 hosts 1) Intermediate host – nourishment for larvae that is different from host of the adult d. Many live in the blood or intestines e. Schistosomiasis – disease caused by blood flukes 1) Results in allergic reactions, swelling ulcers, and liver damage f. Transferred through contaminated water or unwashed hands

III. Phylum: Nematoda A. Roundworms 1. Have a digestive system with two ends 2. Are pseudocoelomates – false body cavity 3. Range from 1mm to 120 cm 4. Have separate sexes and reproduce only sexually 5. Humans are host to about 50 species 6. Ascaris – may cause intestinal blockage a. Eggs or larvae enter body in contaminated food or water. b. Hatch in small intestine and bore through the intestinal wall. c. Enter bloodstream and travel to the lungs. d. Travel up the air passages to the throat.

e. Person coughs, swallows them, and they travel to the intestines.
f. Develop into adults and reproduce. 7. Hookworm – common in the US a. Larvae enter the body by boring through the skin, usually the feet. b. Travel through the bloodstream to the intestines c. Use jaws to attach to the intestinal walls. d. Can cause severe bleeding and may result in anemic conditions. 8. Trichina a. Larvae form cysts in muscles of pigs. b. Humans eat undercooked pork, cysts break open and larvae travel to the muscles and encyst. c. Trichinosis – disease in which cysts form in the muscles.

9. Filaria a. Transferred by mosquitoes b. Invade the lymph system c. Can cause blockage that results in elephantitus 1) Elephantitus – swelling of the limbs (usually the legs)

1. Mantle – soft outer tissue layer on mollusks. a. Secretes the shell
I. Mollusks – include snails, slugs, clams, oysters, octopus, & squid A. Characteristics 1. Mantle – soft outer tissue layer on mollusks. a. Secretes the shell b. Mantle cavity – internal chamber that contains the respiratory structures. 2. Foot – muscular structure used for movement. a. Clams use foot like a shovel b. Snails “slide” on a mucus c. Squid and octopus move by shooting water out of “siphons”

3. Visceral mass – found between the foot and mantle.
a. Contains the internal organs 1) Heart, gonads, and stomach 4. Open Circulatory System – blood is enclosed in vessels in some places, but flows freely over the tissues in other places. a. Simple heart pumps blood through the body B. Body Systems 1. Digestive System – has two openings a. Is a straight tube in some, in others it is coiled 1) Increases the area and allows for more absorption.

2. Reproduction a. Most have separate sexes. b. Fertilization can be internal or external C. Classes of Mollusks – based on shell types, foot structure, & internal body arrangement. 1. Polyplacophora – most primitive mollusks (chitons) a. Shell consists of eight overlapping plates. b. Radula – tongue-like scraping structure used to get food. 1) Scrapes algae off rocks c. Have broad suction foot to cling onto surfaces.

2. Gastropods – one-shelled(Univalves) or no shell
a. Include snails, slugs, & conches b. Nervous system – consists of a small brain and associated nerves c. Gills – respiratory structure adapted for water d. Most that live on land are hermaphrodites. e. Move by muscular contractions of the foot. 3. Bivalves – two-shelled (clams, oysters, scallops) a. Use foot for burrowing into mud or sand. b. Filter feeders – As water passes over the gills, food and sediments are trapped in the mucus. 1) cilia pushes the food to the mouth c. Control flow of water over the body by opening and closing the shell.

4. Cephalopods – head footed mollusk (squid, octopus, nautilus)
a. Most complex and recently evolved of mollusks b. Have tentacles with suckers c. Have a radula and sharp beak-like jaws for feeding d. Closed circulatory system – blood moves through the body entirely enclosed in vessels. 1) Allows for a more efficient gas exchange

D. Mollusks in the Biosphere
1. Valued food in many cultures 2. Also play a role in food chains 3. Used to monitor environmental conditions 4. Some destroy boats and docks made of wood 5. Zebra mussels – originally from Europe a. Accidentally introduced into the Great Lakes b. Reproduce incredibly fast 1) Clog water-intake pipes & farm irrigation pipes.

II. Annelids – Segmented Worms
A. Earthworms – Lumbricus terrestris 1. Has about 100 segments 2. Prostonium – upper lip 3. Each segment has 4 setae – hair-like structures to help them move. 4. Digestive System a. Pharynx – muscular organ that sucks in soil b. Esophagus – tube-like organ connecting pharynx to crop c. Crop – temporary storage area for food. d. Gizzard – very muscular organ that contracts and expands to grind the soil. e. Intestines – digest and absorbs the food.

5. Circulatory System – closed
a. Ventral Blood Vessel – carries blood from anterior to posterior b. Dorsal Blood Vessel – carries blood forward c. Aortic Arches – 5 pairs of tubes that connects the dorsal and ventral blood vessels. 1) Contracts to force blood through the body. 6. Respiration and Excretion a. Can absorb oxygen and release carbon dioxide through the skin. b. Cuticle – outer layer that helps to keep the skin moist. 1) Produces a mucus c. Nephridia – function like kidneys to eliminate nitrogen wastes.

7. Nervous system a. Cerebral Ganglion – found in segment 3 and functions as the brain b. Ventral Nerve Cord – connects brain to ganglia in each segment 8. Reproductive System a. They are hermaphrodites b. Male organs 1) testes – produce sperm (segments 10 & 11) 2) seminal vesicles – store sperm (9-11)

c. Female organs 1) ovaries – produce the eggs (13) 2) oviduct – carry eggs to the genital pore 3) genital pore – eggs leave th worm here (15) d. Seminal receptacle – holds sperm from the other worm. e. Clitellum – swelling involved in reproduction 1) Produces a slime sheath that bring sperm and eggs together

9. Other characteristics
a. Live everywhere but the polar regions and deserts b. Are nocturnal – active mainly at night. B. Classes of Annelids 1. Polychaeta – largest class of annelids a. Are mostly free-living or tube dwelling marine worms b. Parapodia – are “almost feet” that help in locomotion by anchoring the body 2. Oligochaeta a. Includes earthworms and other terrestrial worms.

3. Hirudinea a. Are the leeches b. Most found in fresh water or tropical areas c. Most are blood-sucking parasites. C. Human Uses 1. Help in plant growth by “aerating” the soil and providing nutrients 2. Can be used to remove clotted blood in wounds and help to maintain blood flow. 3. Bait

Mollusks and Segemented Worms
Chapter 22 Mollusks and Segemented Worms I. Mollusks – include snails, slugs, clams, oysters, octopus, & squid A. Characteristics 1. Mantle – soft outer tissue layer on mollusks. a. Secretes the shell b. Mantle cavity – internal chamber that contains the respiratory structures. 2. Foot – muscular structure used for movement. a. Clams use foot like a shovel b. Snails “slide” on a mucus c. Squid and octopus move by shooting water out of “siphons”