LESSON 6: NEMERTINES

• also known as ribbon worms
• • 1,300 species
  • few freshwater and terrestrial
  • majority commonly burrow in marine sediments, or lurking under stones, rock, or mats of algae
  • Long, slender worms rarely exceeding 1m
  • Lineus longgisimus is a boot lace worm that reaches 180ft from Scotland
• Bauplan

  • Proboscis housed in schizocoelous cavity also known as the rhynchocoel
• NERVOUS SYSTEM AND SENSE ORGANS

  • Central Nervous System
  • brain and a pair of longitudinal nerve cords
  • Sense organs includes
  • Epidermal pit
  • Cephalic slits-chemoreceptor
  • Cerebral organs-chemoreceptors
  • Frontal organs-chemoreceptors
• GAS EXCHANGE, INTERNAL TRANSPORT, EXCRETION

  • Coelomic circulatory system: rynchocoel and peripheral vessels
  • Vessels are contractile
  • Vessel fluid may contain pigmented cells including a hemoglobin-containing cell
  • Protonephrida
• REPRODUCTION AND DEVELOPMENT
• REPRODUCTION AND DEVELOPMENT

  • Asexual modes
  • fragmentation and regeneration
• REPRODUCTION AND DEVELOPMENT

  • Sexual mode
  • Most are dioecious
  • Fertilization is external
  • Gonads develop from stem cells
  • Eggs develop in burrows or
  • sediments > zygote > pilidium/pylidium larva > juvenile > adult
  • Protandric