[A] Protochordates

• Protochordates are the informal assemblage of prechordates and primitive chordates
• Protochordate features:

  1. Pelagic larval phase and benthic adult phase
  2. Solitary or colonial
  3. Dioecious and monoecious
• Hemichordates

  • Nervous systems are a network in the epidermis
  • Collar cord - invaginated epidermis and dorsal nerve cord
  • Lack true post-anal tail and notochord
  • Ciliated tornaria larvae, resemble auricularia of echinoderms
• Hemichordate Classes:

  1. Pterobranchia
  2. Enteropneusta
• Hemichordata Cl. Enteropneusta

  1. Marine, live in mucus-lined burrows
  2. Three regions of the body with their own coelom
  3. Proboscis
  4. Collar
  5. Trunk
  6. 3. Stomochord - notochord prerequisite; projects forward into proboscis cavity
• Hemichordata Cl. Pterobranchia

  1. Sessile and colonial, live in secreted tubes
  2. Individuals called zooids
  3. Lacks tubular nerve cords
  4. Collar ganglion in CNS, in the dorsal region of collar
  5. Most species with few pharyngeal slits
• Hemichordates have only some chordate characteristics, and are missing:

  • Notochord
  • Post-anal tail