platyhelminthes

• Turbellarian flatworms are mostly free-living; classes Monogenea, Trematoda, and Cestoda entirely parasitic.
• Bilateral symmetry; definite polarity of anterior and posterior ends; body flattened dorsoventrally
• Body acoelomate.

  Epidermis may be cellular or syncytial (ciliated in some); rhabdites (secrete mucus) in epidermis of most Turbellaria; epidermis a syncytial tegument* in Monogenea, Trematoda, Cestoda, and some Turbellaria.
• Unsegmented worms (members of the class Cestoidea are strobilated).
• Incomplete gut usually present; absent in Cestoida.
• Somewhat cephalized, anterior cerebral ganglion and usually longitudinal nerve cords.
• Nervous system is present
• Most forms monoecious
• Class Turbellaria

  present Rhabdites

  Syncitial Tegument Absent

  Incomplete Digestive Tract

  Planaria

  
• Class Trematoda

  rhabdites absent

  Syncitial Tegument Present

  Anterior Adhesive Organ

  Fluke

  
• Class Monogenea Posterior Adhesive Organ (Opisthaptor)

  
• Class Cestoda Posterior Adhesive Organ (Scolex)

  tapeworm