Platyhelminthes - triploblastic (ectoderm, endoderm, mesoderm)

• level of organization - organs, no organ systems
• body symmetry - bilateral
• alimentary structures - 1-hole sac gut, no digestive cavity
• acoelomate - lacking body cavity (no fluid-filled space involving mesoderm)
• Class Turbellaria - flatworms, aka “Planaria”
  • mostly found in freshwater
  • eyespots - light-sensitive pigmented cups
  • simple nervous system
  • pharynx in middle of body leads to branched gastrovascular cavity
  • extracellular/intracellular digestion in gastrovascular cavity
  • hermaphroditic but not self fertilizing
  • asexual reproduction through regeneration
• Class Tremetoda - parasitic flukes
  • can live inside/outside of hosts
  • no epidermis, covered in epicuticle
  • attaches to host w/ suckers, nutrients absorbed directly
  • mostly hermaphroditic, can self-fertilize, but some dioecious (separate male/female)
• Class Cestoda - tapeworms
  • mostly endoparasites (living inside host)
  • attaches to host w/ scolex
  • proglottid - segmented units, each is hermaphroditic; ones farthest away from scolex are largest, carry eggs
  • no epidermis, covered in epicuticle
  • nutrients absorbed directly (no digestive enzymes/cavity)
  • regeneration possible only if scolex still attached to host
  • tapeworms can self-fertilize

Nematoda - pseudocoelomates (have body cavity between mesoderm/endoderm)

• level of organization - organ systems
• body symmetry - bilateral
• alimentary structures - 2-hole sac gut
• holds internal organs
• triploblastic
• no flagella/cilia, covered in cuticle
• no circulatory system