Small Spider Identification?

[Snailientologist]

I didn't know where to post this since it involves spiders but also myriapods. I found some small spiders living in my millipede terrarium. They would need to have hitchhiked in from some wood that I put into the enclosure that somehow wasn't sanitized properly. They have a strange almost spherical abdomen and very skinny legs. There seem to be two or more different kinds, one with a much larger cephalothorax. This may be two species or some sort of dimorphism? If they have been living there for a while, the only thing they would have had access to for food is springtails and one millipede that was found dead. The size difference between them and the millipedes makes me think they've been feeding on the springtails. They have made small webs in the lower corners from the substrate to about a centimetre up the glass. Any thoughts? Should I be concerned? They were difficult to photograph because they were so small and moved around a lot.

 

[Penn]

If I had to guess I would say they are in the family Linyphiidae. You can compare them to photos on Bugguide.

 

[Cororon]

They are often called "Money spiders", and said to bring monetary luck. You can find them dangling from ceilings indoors, blowing around and end up in your hair outdoors. They build small sheet webs here and there. Harmless cute little Luckbringers.