Flatworms, roundworms and annelids

parasite goals

• reproduce within the definitive host

• fertilised eggs out of host

• recognise and contact new host

• get into new host

flatworms

• no body cavity

• no organs

• one gut enterance

• move using cilia

• many species are parasitic

evolution of digenean life cycle

• life cycle has 5 stages (miracidium, sporocyst, redia, cercaria, metacercaria)

• 2 or more intermediary hosts (1st is a mollusc)

• asexual reproduction in intermediary hosts

• sexual reproduction only in vertebrate definitive host

tapeworms

• non ciliated tegument covers cestodes

• no cell membranes

• no digestive tract

• scolex attaches to intestine buds prohlottids

roundworms

• nematodes

• longitudinal muscle only

• complete gut

• sexes separate

• 20,000 species described

• abundant

• exchange oxygen and nutrients thru cuticle and intestine

annelids

• 15,000 kown species

• metamerically segmented

• segments added infron to pygmidium

• some have set numbers of segments some dont

• body wall with outercircular and inner longitudinal muscle layers

polychaete life habits

• errant

• sedentary burrowers

• sedentary tube formers

medicinal uses of leaches

• clear up discolouration of black eyes

• saliva contains antiinflammatory substances (arthritis)

• leeches used after surgery to promote bloodflow

digestion in leeches

• no amylases, lipases or entoproteases

• medicinal leech digestion is slow

• 200 days to digest 2-3 times its body weight in blood

• no food for upto 18 months

• blood in leech gut dosent oagulate- continues to flow from wound

blood clotting - leeches

• upon injury platelets aggregate on blood vessel wall to form a haemostatic plug

• calin inhibits platelet adhesion and decorsin inhibits platelet aggregation LEECH

• cascade of reactions converts prothrombin to thrombin which catalyses conversion of fibrinogen to fibrin

• hirudin inhibits activaiton of prothrombin LEECH

• fibrin polymerises and threads weave into the plug to strengthen