How many species are out there?

How many species do we share the planet with? The number of described species is over 1 million and counting. but how many others are out there? A new estimate says the rough estimate (but the most accurate one to date) is 8.7 million, including (I'm rounding off a bit here):
- 7.8M animals, the vast majority being uncatalogued insects (We know about 950,000)
- 300,000 plants (we know 216,000)
- 611,000 fungi (we know only 43,000)
- 36,000 protozoa (we know only 8,000)
- 27,500 chromists (13,000 known)

So the idea that we know every species - or even all the "important" species - is ludicrous.