how many water creatures are there? and are there many undiscovered species underwater?

Question: how many water creatures are there? and are there many undiscovered species underwater?
- Keywords:
  ocean,
  species,
  water
Asked by jump45day to Souvik, Sabine, Maria, Armin on 21 Nov 2019.
- Maria McNamara answered on 21 Nov 2019:
  
  This is hard to quantify. We have described up to 250,000 marine species, but it’s estimated that there are many millions more – potentially up to 10 million more – that have not yet been discovered.

Question: how many water creatures are there? and are there many undiscovered species underwater?