• 1) Parasitic classes share many traits with general (dorsoventrally flattened body, blind gut, protonephridia, hermaphroditic) & derived (anterior mouth, neopheran reproductive system) Turbellaria

• 2) Differ from Turbellaria in three ways (lack sense organs, epidermis lacks cilia, have a weird syncytial epithelium with microvilli)

• 3) They have remarkable adaptations to a parasitic lifestyle:
  • a) adults produce massive numbers of gametes
  • b) most have complex life cycles (two or more hosts)
    • final= definitive host is the site of sexual reproduction following extensive asexual reproduction
    • in one or more intermediate hosts they can multiply either sexually or asexually and greatly amplify total fecundity

• 4) Class TREMATODA- (digenic flukes); require 2 hosts; 11,000 spp; incl. some serious human parasites (liver flukes, schistosomes)

  • a) oral (& often ventral) sucker, bulbous pharynx, paired intestines

  • b) Chinese liver fluke has 2 intermediate hosts: i) snail (extensive asexual amplification) and ii) fish or arthropod (no reproduction)

• 5) Class CESTOIDEA- tapeworms (>2 hosts; 3,500 spp); common gut parasites of all vertebrate classes

  • a) distinctive head end (scolex, neck); no mouth or gut
  • b) produce many segments (proglottids) packed with infective larvae
  • c) encyst in intermediate host (enhances ingestion by definitive host)

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