Flatworms and Roundworms and Rotifers 2018.pdf
- 3. Platyhelminthes • Cephalized: They have a head region • Simplest bilaterally symmetrical animal – dorsal, ventral, left, right, anterior and posterior • Dorso-ventrally flattened, distinct posterior and head & soft-bodied (no skeleton)
- 4. Germ Layers • Triploblastic (3 fundamental cell layers – ecto, endo, mesoderm) – In flatworms the 3 germ layers pressed together to form a solid body – acoelomates – no body cavity – All cells are close to the external environment for exchange of gases by diffusion because they are flat and only a few cells thick
- 5. Anatomy •
- 6. Anatomy
- 7. Organization • Organs and organelles • Nerve system of longitudinal fibers not a nerve net • Sexual reproduction • Asexual reproduction by fission • Acoelomates body plan - No circulatory or respiratory system; Only have a digestive tract (gastrovascular cavity for digestion)–that’s why they’re flat • Pharyngeal opening takes in food and expels waste – one way opening • Cephalized = Bilateral symmetry - Sensory organs at anterior end of body • Respiration occurs by diffusion of O2 and CO2 across the body surface directly with environment because they are only a few cell layers thick
- 9. Platyhelminthes • 18,500 species in 3 classes: – Turbellaria (non-parasitic, free living) – Trematoda (parasitic) – Cestoda (parasitic) • No real fossil record - body too soft to preserve well • Believed to have evolved 550 mya
- 10. Class Turbellaria • Free living (planaria best known) • Oceans, fresh water, terrestrial habitats, few are parasitic • Characteristics – The lower surface of turbellarians is ciliated for locomotion; move by muscular contractions – Large eyespots and flaps on sides of head to detect chemicals – Highly branched digestive tract with only one opening – mouth/anus food enters and must be digested before any more food can enter Planaria
- 11. Class Turbellaria Characteristics – Well defined head – Pharynx – muscular tube used to ingest food • Only one opening for digestive system – Have highly branched gastrovascular cavity – Flame cells – collect excess water and transports it through the excretory tubules to remove from body
- 12. Nervous System • Cerebral ganglia – 2 clusters of nerve cells that make up a simple brain • Eyespots – found near cerebral ganglia sense intensity and direction of light • Nerve cords run down sides of body and cross the center like a ladder Eyespots
- 13. Reproduction • Sexual reproduction hermaphrodites produce sperm and eggs • Asexual reproduction- regeneration of missing body parts – worm splits in 2 & regenerates missing half
- 14. Class Trematoda • Flukes – All are parasitic - 9000 species identified – Flukes are leaf shaped worms that parasitize many types of animals – Complex life cycles specialized for parasitism in animal tissues – Fossilized eggs found in Egyptian mummies & sloth dung – Mollusks make pearls around irritating trematode larvae
- 15. Trematoda –Have one or two oral suckers/hooks for attaching to blood vessels near hosts intestine –Mouth at anterior end –Have complete life cycles that can include more than one host –Human liver flukes & blood flukes that cause schistosomiasis have the largest impact on humans Schistosomiasis
- 18. Class Cestoda Tapeworms • Intestinal parasites (adult) in vertebrates • Absorbs nutrients from host • Unsegmented bodies • Head is called a scolex with suckers and hooks to hang on to hose • Tegument keeps them from being digested • No eyes (live in darkness) • No mouth
- 19. Class Cestoda • Reproduces proglottids – rectangular reproductive segments oldest part is furthest from the head with both male and female reproductive organs – Hermophodites • One or more intermediate hosts are invertebrates & primary host is vertebrate • More than 5000 species have been identified • Life cycle – Form cysts when larva burrow into muscle tissue
- 20. Vocabulary Words • Cyst – dormant tapeworm larva with a protective covering • Fission – Usually during the summer the body constricts behind the pharynx while the posterior of the worm is attached to a solid surface and the anterior parts moves forward until the worm splits in 2 and regeneration replaces missing body parts Rabbit w/ tapeworm cysts
- 21. Vocabulary Words • Primary host – host where the adult parasite derives its nutrition and reproduces • Intermediate host - host where the larva derives its nutrition and develops
- 22. Vocabulary Words • Uterus – fluke eggs are stored here until they are ready to be released • Vitellaria – egg yolk glands
- 23. Vocabulary Words • Swimmer’s Itch – minor skin irritation and swelling caused by an allergic reaction to flukes • Schistosomiasis – serious disease where cecaria larva enter through skin in fresh water and into the blood stream where schistosome eggs are laid eventually blocking blood vessels causing irritation, swelling and tissue decay that can lead to death
- 24. Vocabulary Words • Tegument – sheet of fused cells that covers the entire exterior of a fluke • Regeneration – replacement or re-growth of missing body parts Tegument
- 26. Nematoda - Roundworms • Long, slender bodies tapering at both ends • Pseudocoelomates – have a hollow, fluid-filled cavity lined by mesoderm on outside and endoderm on inside • 1 mm to 120 cm (4 feet) long • Have digestive tract with 2 openings (mouth & anus) allows for specialization such as enzymatic digestion and absorption of nutrients
- 27. Nematoda - Roundworms • Separate sexes • Covered by non- cellular protective layer – cuticle • 80,000 known species thought to be 500,000 species • Free living on land, and in fresh and salt water • 150 parasitic species of plants and animals. Humans host 50 parasitic species
- 29. Ascaris • Live in intestines of pigs, horses and humans • Feed on food in the hosts intestines • Can completely block intestine if not treated
- 30. Ascaris • Adult female can grow to 1 foot in length (30 cm) and produce 200,000 eggs EVERY DAY • Male much smaller has hooked posterior end to hold female during mating
- 31. Ascaris Life Cycle • Eggs enter host when eggs are ingested in contaminated food or water • Life cycle: Eggs develop in intestine, larva bore into bloodstream, are carried to lungs, coughed up, swallowed and return to the intestine mature and mate. Eggs are released in feces.
- 33. Hookworms • Intestinal parasite with cutting plates in mouth that hold on to intestinal wall • Feed on host’s blood and can cause anemia. In children can cause delayed mental and physical development.
- 34. Hookworms • Release eggs into host’s feces, larva produced in warm, damp soil, enter host through hosts feet, travel through blood to lungs and throat, swallowing moves them to intestines where they develop into adults. • Infect more than 400 million people worldwide with 90% of infections in tropical and semitropical areas
- 35. Trichinella • Infect humans and other mammals • Infection comes from eating contaminated undercooked meat (pork) then the cysts release larvae that burrow into intestine walls and mature • Cause trichinosis – muscle pain and stiffness can cause death if many cysts form in the heart (muscle). Farmers now cook meat scraps before feeding them to hogs in US lowered infection rate. Also pork is frozen by meat packers killing worms in the US
- 36. Trichinella • Life Cycle: Adults live embedded in walls of host’s intestine, produce larvae that travel through bloodstream to the muscles where they form cysts.
- 37. Other Parasitic Roundworms • Pinworms – infects 16% of adults and children (most common parasite of humans in US). Mate and live in intestine, females lay eggs around anus at night cause itching and are transferred to others from there
- 38. Filarial Worms • Disease causing worm infecting 250 million people a year in tropical areas. Most dangerous live in the lymphatic system. Larva picked up by & develop in mosquito to be transferred to another person where they complete their development. Causes elephantiasis & heartworm
- 39. Rotifera - Rotifers • Pseudocoelomate, transparent, free-living in fresh water • Have a crown of cilia surrounding mouth used to sweep algae, bacteria and protozoans into digestive tract • Can survive without water, dry up, rehydrate and return to living
- 40. ROTIFERA
- 41. Rotifera - Rotifers • Food moves to mastax – muscular organ breaks food into smaller particles to be digested in stomach. Waste passes into cloaca (collection place for digestive, reproductive, and excretory systems) • Use flame cells & excretory tubules to collect excess water. Wastes & water move to anus & are removed. • Cephalized, pair of cerebral ganglia & some have 2 eyespots
- 42. Rotifera - Leishmaniasis • A parasitic disease spread by the bite of the sandfly and can cause skin disease and systemic disease. The systemic form can be fatal, but treatment with antimony- containing compounds produces a high cure rate.