Podocinum vs Pergamasus vs Gamasid mites

Short version of question: How does "Gamasid mites" fit into the classification? I'm especially interested in "Podocinum sp" (assuming the pic I found is correct) which is supposed to be a "Gamasid mite" they say.

Longer version:
I found bugs in plant soil and got worried it came with the palm seeds I planted. Since there are no green parts on the seedling yet the only bugs I could think of were springtails or root mealybug crawlers but they don't look much like mine. I drew a pic which I don't seem to be allowed to show here, but they are light brown, body ½mm long and they look very much like the pic with text "Podocinum sp." under headline "Gamasid mites" here: http://www.massey.ac.nz/~maminor/mites.html

They also look rather similar to Pergamasus but they seem to have a fatter end part of the body so "Podocinum sp." comes closer, in the mentioned pic. The Podocinum pic at bugguide.net doesn't look much like it though (too yellow and too long antennas).

I find these sorted under these headlines:

Mites and Ticks (Acari) » Parasitiformes » mesostigs (Mesostigmata) » Parasitina » Parasitoidea » Parasitidae » Pergamasinae » Pergamasus

Mites and Ticks (Acari) » Parasitiformes » mesostigs (Mesostigmata) » Dermanyssina » Phytoseioidea » Podocinidae » Podocinum

Seems they are not even very closely related?

In the end what I most of all want to find out is if they can be dangerous to plants. The twice as long back legs and quite fast speed I think might suggest they are predators (and the only thing I can imagine there is to eat are springtails)? If so then could I feel assured they wont eat plants?