15.1. Introduction
15.2. Abundance and species succession
15.3. Vertical distribution
15.4. Geographical distribution
      15.4.1. Antarctic
      15.4.2. Arctic
      15.4.3. Atlantic
      15.4.4. Pacific
      15.4.5. Mediterranean
      15.4.6. Indian Ocean, Persian Gulf, and Red Sea
15.5. Seasonal variation
     15.5.1. Arctic and Antarctic
      15.5.2. North Pacific
      15.5.3. Tropics
15.6. Other aspects of distribution
      15.6.1. Blooms
      15.6.2. Appendicularians as indicators of water masses and currents
15.7. Conclusion