Question

Please help with #7

5. What is a proglottid? 6. Why does a tapeworm lack a digestive system? urs Hhough Hherr sLn 7. How do the larval forms of the trematodes and the cestodes differ and how do their life cycles differ? Post-Lab (Laboratory Specimen Notebook Check): TA signature for completion of all drawings and correct labels 122

Answer 1

7. Trematoda and cestoidea are two classes of phylum Platyhelminthes. Tapeworms belong to class cestoda and flukes belong to trematoda. Both class includes parasites of vertebrates.

Larval stages of cestoda includes: onchosphere larva, cysticercus, cystecercoid larva, and hydatid or coracidium, procercoid and plerocercoid larva. First three stages are found in true tapeworms and last three stages are found in false tapeworms.

Larval stages of trematoda includes: miracidium, sporocyst, redia, cercaria, and metacercariae.

Life cycle of tapeworm does not include any asexual stages and has two hosts: definitive host and intermediate host. Intermediate host can be one, two or more. Beef tapeworm which lives in the intestine of humans, proglottids are removed through faeces which contains eggs. These can be eaten by grazing animals cattle, sheep or goat. In intermediate hosts, the onchopshere larva ruptures intestinal wall and reaches to brain and muscles through circulatory system. Here it develops into cysticercus larva and if beef is eaten uncooked or raw, it reaches into human host where larva develops into adult.

In life cycle of trematoda (flukes) i.e. fasciola, adult form lives in the liver of definitive host which is human where they deposit eggs. Immature eggs pass into environment through human faeces. They hatch when comes in conatct of water and form miracidium which then penetrates snail. Sporocyst, redia, and cercaria stage develop in snail tissues and cercaria is released into the water which is a free swimming stage. In water it develops into metacercariae, and cause infection in pigs or humans. In these hosts, metacercariae develops into adult fluke to start the life cycle again.