what’s the most common marine animal? – Marine and Underwater Science Zone

Question: what's the most common marine animal?
- Keywords:
  animal,
  common
Asked by supercalifishagelisticexpialidocious to Dave, Glo, Sean on 23 Jun 2011.
- Dave Sproson answered on 23 Jun 2011:
  
  To be honest I really don’t know! I would assume, if you mean by number, then it would be some sort of zooplankton (tiny animals that form the basis of much of the marine food chain). Maybe Sean can be more specific?
- Sean Clement answered on 23 Jun 2011:
  
  I think Dave is on the right lines there. Although Ozge did mention that the organism with the alargest cumulative biomass (i.e. the weight of every living member of that species put together) is actually Krill! No wonder seeing as that’s all that many WHales in the Polar Oceans east! In terms of sheer numbers, its probably a Planktonic organism such as a dinoflagellate. Nothing too big or cool really but its those very, very tiny creatures that form the most important links in Marine food webs. Without them, nothing else would be alive!

Question: what's the most common marine animal?