Platyhelminthes pt 2 Digene trematodes and tapeworms

Turbellaria Monogenea Trematoda Cestoda Cilia lost from ectoderm (parasitic lifestyle) Microtriches Scolex Proglottids Acetabulum endoparasite Mollusc/vertebrate life cycle Opisthaptor Ectoparasite One host Free living Phylum Platyhelminthes

Di(2)-Gene(birth) 2 or more hosts Endoparasitic No cilia on skin, skin is syncytial Life cycle: Adults in definitive host (a vertebrate) reproduce sexually → eggs in host’s feces released into water → hatch into ciliated larva (=miricidium) → snail (intermediate host) → asexual reproduction → sporocyte → redia → cercaria released from snail → metacercaria encysts in 2 nd intermediate host (or forage in some cases) → ingested by definitive host

Schistosoma mansoni

200 million infected worldwide Leading cause of death of Egyptian men years old Adults live in mesenteric veins, veins associated with bladder Damage caused by unegested eggs (50% never released) Control: clean water, sewage control, snail reduction Exacerbating factors: poverty & ignorance, dams

Swimmer’s itch Schistosoma sp. that infect ducks, muskrat

Blackspot disease: Uvulifer sp.

Fasciola hepatica (sheep liver fluke) F. gigantica (human liver fluke)

Dicrocoelium dendriticum = a bile duct fluke of ruminants such as sheep, goats, deer, pigs.

Tuesday November 13 th CMU Ballroom Make a team of 3 – 4 students & sign up on the poster outside SL 118 by October 16 th !! For more information: Tri-Beta Meeting October 2 nd 6:00 SL118 Chem Club Meeting October 3 rd 7:00 HA 405 Or contact Marissa Schafer at

Turbellaria Monogenea Trematoda Cestoda Cilia lost from ectoderm (parasitic lifestyle) Microtriches Scolex Proglottids Acetabulum endoparasite Mollusc/vertebrate life cycle Opisthaptor Ectoparasite One host Free living Phylum Platyhelminthes

Class Cestoda - Tapeworms Obligate endoparasites of vertebrates Lack digestive tract Have scolex for attachment to host Body divided into proglottids –Each proglottid = egg factory with its own ovary and testis (make up to 50,000 eggs per proglottid) –Worm = hundreds to thousands of proglottids

General life cycle of tapeworms Adult in intestine of definitive host → proglottids break off and pass with feces → eggs released from proglottid → eaten by intermediate host → oncosphere larva → intermed host ingested by definitive host → adult develops in intestine

Tapeworms Scolex

Echinococcus granulosis – a tapeworm of dogs & dingoes

Dipylidium caninum

Beef tapeworm: Taenia saginata Attains a length of 10m

Ligula intestinalis Egg → copepod (encycts as a procercoid) → fish (encysts as a plerocercoid larva) → ingested by final host → adult tapeworm in gut of bird