Friday Riddle / Teaser

I think I found one that will actually be hard

RIDDLE: Hello there!

I am a living animal.
You may not see me with your eyes,
But though I'm very, very small,
I'm a tough nut for my size.

I do not fear the arid desert,
Nor the frigid cold and snow.
I can rest comfortably in the mountains high
Or in the ocean far below.

You may find me in the cold of space
Or by a pristine, little lake.
I may have gone thirsty for 100 years,
So give me a drink, for goodness sake!

If you find me, please say "hello,"
And a new friend you can make,
For you'll find I'm not as nasty
As my more ferocious namesake.

It's been a pleasure meeting you
And telling you about me.
Now that you have all the clues,
Please tell me, what can I be?