Hi Megan,
When you say slugs.., do you mean to say clear looking bugs-like critters?
You can read more about various small critters that are commonly seen in the aquariums
here, and
here and also
here
If it isn't that, please let us know so we can do some more guessing...
As far as those orbs go, do they have a stalk/column?
It;s very hard to guess as to what the animal may be without seen it, though.