Platyhelminthes II Post-Notes October 2024 PDF

Summary

These notes provide an introduction to Platyhelminthes, focusing on parasitic strategies of trematodes and cestodes. Diagrams and descriptions of various life cycle stages are included. The notes are likely for a biology class, possibly at an undergraduate level.

Full Transcript

3 INTRODUCTION Phylum Platyhelminthes Class Turbellaria Trematoda Monogenea Cestoda Lifestyle free living parasitic parasitic parasitic Parasitic internal external internal...

3 INTRODUCTION Phylum Platyhelminthes Class Turbellaria Trematoda Monogenea Cestoda Lifestyle free living parasitic parasitic parasitic Parasitic internal external internal mode Digestive present present present absent tract 18 PARASITIC STRATEGIES - CESTODES Strobila - the body of the worm from behind the scolex - a chain of proglottids Scolex - specialized structure for attachment to host intestinal epithelium 19 PARASITIC STRATEGIES - CESTODES Proglottid - a reproductive “section” - each proglottid contains both male and female reproductive systems Strobila - No digestive system, epidermis - the body of the worm (tegument) has microtriches, from behind the scolex similar to microvilli/ increase - a chain of proglottids surface area for absorption of nutrients. Scolex - specialized structure for attachment to host intestinal epithelium 20 PARASITIC STRATEGIES - CESTODES germinative zone (new proglottids produced) - gonadal material in a proglottid matures as it moves posteriorly - gamete exchange occurs between proglottids of different worms or of the same worm - immense reproductive capacity! - individuals of large species can produce up to 1 000 000 eggs / day 20 PARASITIC STRATEGIES - CESTODES germinative zone (new proglottids produced) - gonadal material in a proglottid matures as it moves posteriorly - gamete exchange occurs between proglottids of different worms or of the same worm - immense reproductive capacity! - individuals of large species can produce up to 1 000 000 eggs / day 21 PARASITIC STRATEGIES - CESTODES Beef tapeworm – Taenia saginata (Example of Lifecycle of Cestodes) 1. Gravid proglottid shed in faeces and shelled larvae (oncospheres) develop 2. Shelled oncospheres ingested by cattle 3. Shelled oncosphere larvae hatch and lyse through intestinal wall 4. Larvae take up residence as a cyst* in intermediate host muscle. 5. *Cyst = cysticercus, (bladder worm) scolex invaginated 6. When ingested by definitive host, cyst wall dissolves, scolex evaginates and bladder worm attaches to intestine. Worm matures in 2-3 weeks. CBC NEWS: For this Alberta woman, the good news was she had contracted a rare, deadly parasite 22 PARASITIC STRATEGIES - TREMATODES Key Features 1. Life cycle typically includes 5 developmental stages 2. Life cycle typically includes 2 or more intermediate hosts 3. Species specificity for 1st intermediate host always high 4. Specificity for other intermediate, and definitive, hosts low 5. Adulthood only achieved in a definitive vertebrate host 6. Life cycle includes asexual replication of developmental stages, normally in 1st intermediate host 23 PARASITIC STRATEGIES - TREMATODES Adult Lives in definitive host. Hosts in all vertebrate groups. Infestation can occur in virtually any organ system (e.g. liver flukes, blood flukes, lung flukes, urinary tract flukes, reproductive tract flukes). Egg containing miracidium (1st developmental stage) Egg usually released in feces, must reach water. Miracidium, free-living ciliated larval stage that penetrates the epidermis of the first intermediate host (usually a snail) penetration gland germ balls 24 PARASITIC STRATEGIES - TREMATODES Miracidium: Develops into a Sporocyst once inside intermediate host (snail) Sporocyst (2nd developmental stage) Sporocyst reproduces asexually to yield more sporocysts OR rediae. (In this manner, a single egg can give rise to a large number of progeny.) embryo (from the germ balls) (developing redia or sporocysts) 25 PARASITIC STRATEGIES - TREMATODES developing cercariae Rediae (3rd developmental stage) Sac-like structure containing developing Cercariae. Rediae in turn also reproduce asexually to produce more cercariae, further increasing the number of progeny arising from the original single egg. 26 PARASITIC STRATEGIES - TREMATODES Cercariae and Metacercariae (4th & 5th developmental stages) Free swimming cercariae emerge from snail host and penetrate epidermis of a second intermediate host (could be a fish for example….OR some wait in host to be eaten) oral sucker ventral sucker muscular tail cercariae 27 PARASITIC STRATEGIES - TREMATODES Cercariae and Metacercariae (4th & 5th developmental stages) Free swimming cercariae emerge from snail host and penetrate epidermis of a second intermediate host (could be a fish for example…OR some wait in host to be eaten) The cercariae encysts in the skin or muscle of second intermediate host, becoming a metacercariae. Metacercariae are eaten by the definitive host. oral sucker ventral sucker muscular tail metacercariae cercariae 28 PARASITIC STRATEGIES - TREMATODES Definitive Host (a vertebrate animal, humans) First Intermediate Host (usually a snail) Second Intermediate Host (example: a fish) Adult Metacercariae Miracidium Cercariae Sporocyst Rediae 29 PARASITIC STRATEGIES - TREMATODES Clonorchis sinensis – Chinese liver fluke Metacercaria Adult fluke Egg with miracidium Cercaria Miracidium hatches in water and penetrates snail Redia Sporocyst

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