Worms

1. Worms MATES

2. Bilateral Symmetry • Cut body one way = 2 identical halves (fig7.12b, p.120) • (bi = two, latus = side). • Orientation includes: • Anterior • Posterior • Dorsal • Ventral

3. Symmetry Comparison

4. FlatwormsPhylum Platyhelminthes • Simplest – dorsoventrally flattened (flat backs & bellies) • triploblastic (composed of three fundamental cell layers) • Real organs & organ systems • no body cavity other than the gut • Central nervous system = simple brain (aggregation of nerve cells) • lack an anus; the same pharyngeal opening both takes in food and expels waste • must respire by diffusion, and no cell can be too far from the outside, making a flattened shape necessary

5. Platyhelminthes • Life without a coelom : The image at left is a fluke (possibly a species of Probolitrema). Flukes, like other parasitic flatworms, have complex life cycles often involving two or more host organisms. At right, a planarian (Dugesia). Planarians are free-living flatworms, and have a much simpler life history. They inhabit freshwater, and are carnivores (even without teeth) or scavengers. Most are less than a centimeter long.

6. Marine Flatworms • Marine flatworms : The marine flatworms (polycladids) are the largest of the free-living flatworms, sometimes reaching lengths of 15 centimeters. Polycladids get their name from their highly branched digestive cavity. These individuals were photographed on a reef near the island of Guam.

7. 3 Groups of Flatworms • 1. Turbellaria-free-living, include the planarian, Dugesia, found in the oceans, fresh water, & in moist terrestrial habitats, a few are parasitic

8. 2. Trematoda, or flukes, all parasitic, have complex life cycles specialized for parasitism in animal tissues. Members of one major taxon of flukes, the Digenea -- which includes the human lung fluke -- pass through a number of juvenile stages that are parasitic in one, two, or more intermediate hosts before reaching adulthood, at which time they parasitize a definitive host. • Flatworms include non-parasitic worms such as planaria, which live in water, and parasitic flukes and tapeworms. The human liver fluke infects over 75% of the people in parts of Japan, China, and South Asia. The adult fluke, about 3/4 inch long, lives in the bile ducts of the liver; its eggs (1) pass from the body in the feces. The eggs, containing larvae, are eaten by water snails (2) and then develop into another form, which passes into the water. They then bore into the bodies of fishes (3). When raw fish is eaten (4) - as is common in the Orient - the young worms swim from the intestine into the fine branches of the bile duct and grow to maturity.

9. 3. Cestoda, or tapeworms, are intestinal parasites in vertebrates, and they also show anatomical & life history modifications for parasitism. Use suckers or hooks to latch on 50 ft worm found in Sperm Whale

10. Beef Tapeworm - The cestodes (tapeworms) Taenia saginata (beef tapeworm) and T. solium (pork tapeworm).  Taenia solium can also cause cysticercosis. Life Cycle:

11. Ribbon WormsPhylum Nemertea • about 900 known species (fig.7.14, p.121) • the European nemertine Lineus longissimus has been known to reach 30 meters (nearly 100 ft) in length, • Most nemertines are marine • Proboscis-wraps around the prey, and toxic secretions immobilize the prey • Stylet-piercing barb • nemertines are carnivorous; most feed on small invertebrates like crustaceans and annelids, but some feed on the eggs of other invertebrates, and a few live inside the mantle cavity of molluscs and feed on microbes filtered out by the host. • nemertines have major features that flatworms lack, notably a complete gut with an anus, and a system of blood vessels. This vessel system may in fact be homologous with the coelom, or fluid-filled lined body cavity • True organsw/ organ system & central nervous system

12. Proboscis • Prostoma rubrum, an example of the phylum Nemertea, with its long proboscis everted. • Fig 7.14, p. 121

13. Nematodes - RoundwormsPhylum Nematoda • Nematodes are the most numerous multicellular animals on earth • Most common in soil & marine sediments • nearly 20,000 described species (>500,000 total) • 1,000 somatic cells • possess digestive, nervous, excretory, and reproductive systems, but lack a discrete circulatory or respiratory system • range from 0.3 mm to over 8 meters • The largest nematode ever observed is Placentonema gigantisma, discovered in the placenta of a sperm whale w/ 32 ovaries • Found inhabit intestines of seals & dolphins & flesh of fish (sashimi) • Humans - hookworm, trichinosis and elephantiasis

14. Intestinal Roundworms, of which Ascaris is a common form, infect wild and domestic animals and man. Eggs drop to the ground in animal feces. Humans are infected by eating contaminated food. The diagram at right shows the life history of Ascaris. Eggs hatch into larvae in the intestinal tract and bore through intestine wall (1). Blood carries larvae to lungs (2), where they grow. They are then coughed up or crawl up windpipe to back of mouth (3), are swallowed (4), and mature in intestine (5). A female worm living in the intestine may have millions of eggs in its body. These pass out in feces (6) and, if eaten by other animals, start the life cycle over again. Hookworm, once a serious disease in the southern U.S., is still common in the warm areas of the world. Infected people lack energy. The hook-worm life cycle is like that of intestinal roundworms except that infection occurs as larvae hatched in the warm soil bore through the skin, usually on the soles of the feet, to enter the blood.

15. Trichina Worm • Round Worm • The trichina worm lives inside the small intestine of a host animal, where it mates and reproduces. Once her eggs have been fertilized, the female burrows into the intestinal wall and releases her larvae. The larvae migrate into the lymph channels of the intestine, from which they enter the bloodstream and travel to all parts of the body. When the larvae reach the skeletal muscles they burrow into the muscles and form tough cyst-like cocoons. The host secretes lime salts, which are deposited in the capsule, eventually transforming the capsule into a completely calcified cyst. The worms may live in the cyst for years until they are consumed and digested by another mammal.

16. Nematode Worms • Marine Nematode - Draconema

17. Here Parborlasia corrugatus worms are eating fish eggs. P. corrugatus has a one-way gut with a large mouth and a closed circulatory system; nemertean worms are the simplest animals with a circulatory system. Like other proboscis or nemertean worms, the wedge-shaped head of P. corrugatus has a fluid-filled cavity used to rapidly shoot a barbed proboscis which the worm uses to capture prey and defend itself [1]. This harpoon-like proboscis has adhesive secretions which secure prey. P. corrugatus is chemically defended by an acidic mucus (pH 3.5) which potential predators avoid [4].

19. Segmented WormsPhylum AnnelidaEverybody's favorite, worms. . . • earthworms, leeches, polychaetes • about 9000 known species • Segmentation • Hydrostatic Skeleton • Coelom • Cerebral Ganglion

20. Polychaete WormsClass Polychaeta • Mostly marine- 10,000 species • 2-4 in. • Proboscis w/ jaws • Parapodia – flattened extensions • Setae – bristles (Fig. 7.15) • Closed Circulatory System • Gills w/ capilaries on parapodia & body allow respiratory exchange

21. Polychaete External Anatomy

22. More Polychaetes • Oligochaetes – small, live in mud/sand (p.273) • Marine relative of earthworms • Lack parapodia

23. And More Polychaetes • Leeches (Class Hirudinea) – mostly FW, marine species are found attached to fish & inverts (parasitize) • Sucker at each end w/ no parapodia • hermaphroditic

24. Phylum Pogonophora • Beard Worms (pogonophorans) – lack a mouth and gut (fig. 7.17) – use symbiotic bacteria to manufacture food. • 4in.-7ft. – Read p.125 • Vestimentiferans – hydrothermal vent worms

25. Leeches in the eye of an unfortunate soul who drank from the wrong pond in India. Probably Hirudinaria granulosa. - Mark E. Siddall

26. Peanut WormsPhylum Sipuncula • Soft, unsegmented bodies (fig. 7.18, p.124) • 320 known species • .4in.-14in. • Deposit feeders • Peanut shaped

27. EchiuransPhylum Echiura • Marine • Look like soft unsegmented sausages buried in mud/sand • Spoon-like or forked proboscis (fig 13.9, p.272) • Deposit feeders