Platyhelminthes pt 2
Digene trematodes and
tapeworms
Opisthaptor
Ectoparasite
One host
Monogenea
Turbellaria
Trematoda
Acetabulum
endoparasite
Mollusc/vertebrate
life cycle
Cestoda
Free living
Microtriches
Scolex
Proglottids
Cilia lost from ectoderm
(parasitic lifestyle)
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 2nd intermediate host (or
forage in some cases) → ingested by definitive host
Schistosoma mansoni
200 million infected worldwide
Leading cause of death of Egyptian men 20-44 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 13th
CMU Ballroom
Make a team of 3 – 4 students & sign up
on the poster outside SL 118 by October
16th!!
For more information:
Tri-Beta Meeting October 2nd 6:00 SL118
Chem Club Meeting October 3rd 7:00 HA 405
Or contact Marissa Schafer at marissaschafer@hotmail.com
Opisthaptor
Ectoparasite
One host
Monogenea
Turbellaria
Trematoda
Acetabulum
endoparasite
Mollusc/vertebrate
life cycle
Cestoda
Free living
Microtriches
Scolex
Proglottids
Cilia lost from ectoderm
(parasitic lifestyle)
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