Understanding Platyhelminthes, Nematoda, and Annelida: The Diversity of Worms

1. Chapter 27Worms

2. 27-1 Flatworms • Phylum Platyhelminthes • Soft • Flattened worms • Have tissues of an internal organ system • Acoelomates • Only digestive cavity • Simplest animal to have • Bilateral symmetry (left to right) • Cephalization

3. Form and Function • Free-living • Organ systems for digestion, excretion, respiration and reproduction • Parasitic • Simpler in structure without (or with modified) internal organs ex. Fluke • All rely on diffusion for something

4. Form and Function • Feeding • Free-living • Carnivores- eat tiny aquatic animals • Protostomes • Pharynx- muscular tube pumps food into body • Parasitic • Feed on blood, tissues or pieces of cells • Obtain nutrients from food digested by host • Non-complex digestive system

5. Form and Function • Resp, Circ, and Excretion • Diffusion to transport oxygen and nutrients • Response • FL- head encloses ganglia- cells that control the nervous system • Eyespot- group of cells that detect change in light

6. Form and Function • Movement • FL- cilia help glide in water • Muscle cells allow twist and turn for reaction • Reproduction • FL- hermaphrodites • Sexual- exchange sperm then lay egg • Asexual- fission- organism splits in two and each becomes a complete organism • Parasitic- complex cycles between sexual and asexual

7. 3 main groups of flatworms • Class Turbellaria • FL in marine or fresh water • Bottom dwellers in sand or mud • Great variation in color, form and size • Class Trematoda- flukes • Parasitic- infect internal organs of host • Schistosoma mansoni • Lives in humans, reproducing sexually • Burrow through exposed skin • Carried to blood vessels of intestines • Have an intermediate host in water- snail • Schistosomiasis- their eggs clog blood vessels- swelling

8. Class Cestoda- tapeworms • Parasitic, long, flat, live in intestines • No digestive tract- absorb through body walls • Scolex- head of an adult tapeworm with suckers • Proglottids- the segments that make up the body • Contain both male and female reprod. Organs • Egg is fertilized then they break off and burst

9. 27-2 Roundworms • Phylum Nematoda • Slender, unsegmented with tapering ends • Pseudocoelom “false coelom” • Digestive tract with two openings • Undigestable food leaves through anus

10. Form and Function • Feeding • FL- predators use mouthpart • Some eat algae, fungi and decaying matter • Resp, Circ, and Excretion • Diffusion through body walls • Response • Ganglia • Sense organs- detect chemicals from prey

11. Form and Function • Movement • Hydrostatic skeleton • Move like snakes with muscle contraction • Reproduction • Sexually- separate genders • Internal fertilization

12. Human Diseases • Trichinosis • Caused by Trichinella • Live in intestines • Female releases larvae into bloodstream • Forms cysts and becomes inactive in muscles • Filarial worms • Live in blood and lymph vessels of birds and mammals • Transmitted through insect bites • Blocks the passage of fluids in lymph vessels • ex) Elephantiasis

13. Human Diseases • Ascarid • Ascaris lumbricoides • Causes malnutrition by absorbing digested food from small intestine of host • Carried in blood until it reaches the lungs then moves to throat and swallowed back in intestine • Hookworms • Use sharp plates and hooks to burrow into skin • Enter bloodstream • Cause weakness and poor growth

14. 27-3 Annelids • Phylum Annelida “little ring” • Segmented worms • Segments are separated by septa • Each segment is specialized • True coelems made from mesoderm tissue • Mouth to anus digestive tract

15. Form and Function • Feeding and Digestion • Filter feeders to predators • Earthworms- pharynx moves food into esphogus to the • Crop- where the food can be stored, to the • Gizzard- where its ground into small pieces • Absorbed by the intestines

16. Form and Function • Circulation • Closed circulatory system- blood is contained in a network of blood vessels • Two major blood vessels- dorsal (tail to head) and ventral (head to tail) • Dorsal contracts rhythmically and pumps like a heart • Respiration • In water, breathe through gills • On land, the respire through moist skin

17. Form and Function • Excretion • Digestive waste passed through anus • Cellular waste passed by nephridia- excretory organs that filter fluids from coelem • Response • Brain and several well developed nerve cords • Sensory adaptations- tentacles, chemical receptors, statocysts, 2+ pairs of eyes

18. Form and Function • Movement • Hydrostatic skeleton • Longitudinal muscles- from front to back contract • Circular muscles- around each segment, long, thin • Marine- use parapodia for swimming/crawling • Reproduction • Sexually (most)- external fertilization- diff sexes • Earthworms and leeches- hermaphrodites • Clitellum- mucus ring where egg and sperm are release for fertilization– it slips off to protect eggs

19. Groups of Annelids • Class Oligochaeta “few hairs” • Earthworms- streamlined with little setae • Live in soil or fresh water • Class Hirudinea- leeches • External parasite- sucks blood and fluid from host • Uses suckers to slice and proboscis to suck • Used to reduce swelling, pressure and clotting • Class Polychaeta “many hairs • Sandworms, blood worms • Marine with paired appendages with setae