26.3 Section Objectives – page 706 Unit Objectives: Objective 1: Describe the form and function of the flatworms Objective 2: Differentiate the classes of the Phylum Platyhelminthes (Turbellaria, Trematoda, Monogenea, Cestoda) Objective 3: Describe the form and function of the organisms in Phylum Nematoda Objective 4: Differentiate the classes of the Phylum Rotifera (Csisonidea, Bdelloidea, and Monogonomonta). Objective 5: Describe the form and functions of the organisms in the Phylum Rotifera Objective 6: Explain the characteristics of various parasites found in the Phylum Platyhelminthes. Objective 7: Explain the characteristics of various parasites found in the Phylum Nematoda Objective 8: Explain the characteristics of various parasites found in the Phylum Rotifera. 26.3 Section Objectives – page 706

Classes of Planarians (Obj 2) Cestoda- Tapeworms Trematoda-Flukes Turbellaria-Free Living Flatworms Monogenea-Flatworms that live in the gills of fish

What is a flatworm? The least complex worms belong to the phylum Platyhelminthes (pla tee HEL min theez). These flatworms are acoelomates with thin, solid bodies. Planarian

What is a flatworm? There are approximately 14,500 species of flatworms found in marine and freshwater environments and in moist habitats on land. Planarian

What is a flatworm? The most well-known members of this phylum are the parasitic tapeworms and flukes, which cause diseases in other animals, among them frogs and humans. The most commonly studied flatworms in biology classes are the free-living planarians.

Section 26.3 Summary– pages 706-710 Nervous control in planarians Most of a planarian’s nervous system is located in its head—a characteristic common to other bilaterally symmetrical animals. Nerve cell mass Section 26.3 Summary– pages 706-710

Nervous control in planarians Some flatworms have a nerve net, and others have the beginnings of a central nervous system. Nerve cell mass

Nervous control in planarians A planarian’s nervous system includes two nerve cords that run the length of the body. Ganglia Eyespots Nerve cord Muscle cells

Nervous control in planarians It also includes eyespots that can detect the presence or absence of light and sensory cells that can detect chemicals and movement in water. Ganglia Eyespots Nerve cord Muscle cells

Nervous control in planarians At the anterior end of the nerve cord is a small swelling called a ganglion (plural, ganglia). The ganglion receives messages from the eyespots and sensory pits, then communicates with the rest of the body along the nerve cords. Ganglia Messages from the nerve cords trigger responses in a planarian’s muscle cells.

Reproduction in planarians Like many of the organisms studied in this chapter, most flatworms including planarians, are hermaphrodites. During sexual reproduction, individual planarians exchange sperm, which travel along special tubes to reach the eggs.

Reproduction in planarians Fertilization occurs internally. The zygotes are released in capsules into the water, where they hatch into tiny planarians.

A Planarian Eyespots Head Sensory cells Extended pharynx Flame cell Mouth Extended pharynx Digestive tract Flame cell Cilia Nucleus Excretory system Cilia

Reproduction in planarians Planarians also can reproduce asexually. When a planarian is damaged, it has the ability to regenerate, or regrow, new body parts. Regeneration is the replacement or regrowth of missing body parts.

Reproduction in planarians If a planarian is cut horizontally, the section containing the head will grow a new tail, and the tail section will grow a new head.

Section 26.3 Summary– pages 706-710 Reproduction in planarians Thus, a planarian that is damaged or cut into two pieces may grow into two new organisms—a form of asexual reproduction. Section 26.3 Summary– pages 706-710

Feeding and digestion in planarians A planarian feeds on dead or slow-moving organisms. Extended pharynx It extends a tube-like, muscular organ, called the pharynx (FAHR inx), out of its mouth. Enzymes released by the pharynx begin digesting food outside the animal’s body.

Feeding and digestion in planarians Food particles are sucked into the digestive tract, where they are broken up. Cells lining the digestive tract obtain food by endocytosis. Food is thus digested in individual cells.

Feeding and digestion in parasitic flatworms Hooks A parasite is an organism that lives on or in another organism and depends upon that host organism for its food. Scolex Sucker Proglottid Parasitic flatworms have mouthparts with hooks that keep the flatworm firmly attached inside its host. Mature proglottid with fertilized eggs

Tapeworm bodies have sections Hooks The body of a tapeworm is made up of a knob-shaped head called a scolex (SKOH leks), and detachable, individual sections called proglottids. Scolex Sucker Proglottid Mature proglottid with fertilized eggs

Tapeworm bodies have sections Hooks A proglottid (proh GLAH tihd) contains muscles, nerves, flame cells, and male and female reproductive organs. Flame cells remove excess water from a planarians body. The water from flame cells collects in tubules and leaves the body through pores in the body surface. Scolex Sucker Proglottid Mature proglottid with fertilized eggs

Types of Tapeworms (Obj 6) -Beef Tapeworm (Taenia saginata): Lives in the intestines of humans. They contain proglottids which can reach a length of 10 m or more. Proglottids detach and pass in feces. Gravel proglottids crawl out of feces onto nearby vegetation. There they may be eaten by grazing cattle. A proglottid ruptures as it dries and scatter embryos on soil and grass. Embryos may remain viable on grass for as long as 5 months. Once eaten by the cattle, they develop as cysts in the muscles of the cow. See Fig 14-19. -Pork Tapeworm (Taenia solium (Paragonimus): Wild carnivores, humans, pids, and rodents. The infected host coughs up eggs in the sputum. The sputum is swallowed and released in the feces in the water. The zygotes develop in the water into miracidia which then penetrate a snail host. In the snail, the miricidia develop into sporocysts then into cercaria. These cercaria are shed in the water and ingested directly by freshwater crabs which prey on snails. Infection of the host is by eating raw or undercooked crab meat. -Fish Tapeworm (Diphyllobothrium latum): Adult tapeworm found in the intestine of humans, dogs, cats and other mammals. The immature stages of the parasite develop in crustaceans and fish. Fish tapeworm can occure anywhere where raw fish is eaten. In the US, infection is most common in the Great Lakes region. -Dog Tapeworm (Diphlydium caninum or Chinoccus granulosus): Causes hydatidosis (cysts in the liver) in humans. Can develop in canines, humans, monkeys, sheep, reindeer, and cattle. The cysts which develop grow slowly. The cysts can bud off and contain thousands of scolices. Each scolex will produce a new worm when eaten by a canine.

Types of Flukes (Obj 6) Liver Fluke in humans (Clonorchis sinensis): Hosts include humans, cats, dogs, and pigs. Adult Flukes live in the bile passageways of humans, cats, dogs, or pigs. Eggs are shed into the water with feces. Once the feces and eggs are ingested by snails, the eggs develop into a sporocyst. They travel to the water and swim until they encounter a fish in the family Cyprinidae (minnow family). If the human or animal eats the undercooked fish, they develop into young flukes and complete the cycle. See Fig 14-12. -Blood Fluke (Schistomoma): Hosts include humans. Eggs are released in human feces or urine into the water and hatch as ciliated miracidia. The miracidia are then in contacted by a snail and transform into sporocysts. The sporocysts then develop into cercariae and leave the snail into the water. The cercariae can penetrate the skin of a human and infect another human. See Fig 14-13. -Lung Fluke (Paragonimus): Wild carnivores, humans, pigs, and rodents. The infected host coughs up eggs in the sputum. The sputum is swallowed and released in the feces in the water. The zygotes develop in the water into miracidia which then penetrate a snail host. In the snail, the miricidia develop into sporocysts then into cercaria. These cercaria are shed in the water and ingested directly by freshwater crabs which prey on snails. Infection of the host is by eating raw or undercooked crab meat.

The life cycle of a fluke Adult flukes Embryos released Larva Human host Snail host

Tapeworm bodies have sections Some adult tapeworms that live in animal intestines can be more than 10 m in length and consist of 2000 proglottids.