Hello sdcp!
You can easily find such things online, for example in
Wikipedia.
In Polish it is officially called atka, but commonly małpa (monkey) or małpka (little monkey).
But let's wait if Polish natives come up with more pet names for it.
I only use and came across
małpa--it's what everyone uses
. I never heard the other two names, I must admit. I could understand
małpka but
atka is like a diminutive from English
at that sounds odd to me.

Anyway, I prefer the old pet
małpa--it sounds so funny along with some (nick)names.
Tom