I'm absolutely full of pairs,
And that's why I'm important.
If my owner's used to describe me,
I'd be like just a pair of letters.
With the first pair, I'm from a plant or animal.
With the second pair, you won't see me at all.
With the third pair, you'll hear me instead.
With the fourth pair, I'm out in the open.
What am I?
I'm glad that someone (Tom) fell for the red herring of assuming the answer must be an eight-letter word with each of the last four lines referring respectively to its pairs of letters. But that's not the right solution method.
Edit: nearly two years down the line, I'm ashamed to admit that I've actually forgotten my own solution to this. So here's some hints/guesses based on what little I can remember or what I know about my own riddling style:
Line 2 must be just fluff, but line 3 has got to have some very specific (but possibly very obscure) meaning. Line 4 probably refers to a homophone of a pair of letters (e.g. MT ~ empty, that kind of thing).
I'm racking my brains to remember what I meant by the "first pair", "second pair", etc. The only thing I'm coming up with, possibly, is that it might have been somehow intended to relate to numbers, like multiples or powers of two. Maybe the 2nd, 4th, 6th, 8th or 2nd, 4th, 8th, 16th letters of the alphabet???