Platyhelminthes

Platyhelminthes

1. Free-living

   • living independently from other organisms
   • Class Turbellaria
     • Locomotion
       • Undulatory Swimming
         • Swimming via waves on muscle contraction
       • Ciliary Gliding
         • movement along a surface propelled by cilia and using muscles to reduce friction
     • Nutrition and Feeding
       • Incomplete Gut
         • one opening = mouth
         • highly branched to distribute nutrients
       • Pharynx may be present
         • may be extended from the body or withdrawn into the pharyngeal cavity
       • Scavengers and Predators
     • Nervous System & sensory structure
       • Ladder-like nervous system
         • true cephalization
         • anterior cerebral ganglion
         • longitudinal nerve cords
         • transverse connectives
       • Concentration on the head
       • Sensory Structures
         • Chemoreceptors
           • detect chemicals and abundant on auricles
         • ocelli
           • eye spots that detect light but cannot form an image

2. Commensalism

   • living in close association with other species
     • species benefits & its partner is unaffected
     • Ex: Limulus leeches - flatworms that attach to horseshoe crabs & gain transportation/food but do no harm
   • Class Turbellaria
     • exhibits cephalization
       • mouth is located on the ventral side at the end of a tubular pharynx
         • ciliated epithelium with several mucous glands
           • 3 different layers of well developed muscles weft together
             • circular
             • diagonal
             • longitudinal
     • acoelomate body plan

3. Parasitism

   • species live in close association
     • one species benefits while the host is harmed
   • Class Cestoda: Tapeworms
     • Class Monogenea: Flukes
       • Class Trematoda: Flukes

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