Ants are probably by far the greatest number of individual animals on Earth. They live everywhere, except the universe likes cruel irony.
No ants in ANTartica!!!
Amongst the plant or plantlike species, the greatest population is prochlorococcus. A marine micro-photosynthetic bacteria. Worldwide, in the oceans, there are probably 1-100 billion billion billion of them. Estimate are that they produce 20% of the oxygen on the planet.
And nobody ever heard or saw or thought of them until about 1978.
I wonder what else is undiscovered.
That is ironic. And thanks.
Prochlorococcus links:
http://genome.jgi-psf.org/prom9/prom9.home.html
Prochlorococcus images:
http://www.google.com/images?q=prochlorococcus&sa=X&oi=image_result_group