I just bought a brand new single speed bike from my local bike store. the store is quite far away, so I'm hoping someone here might be able to help vs me going back to the shop to ask questions. I tried calling them but had a hard time explaining it.

I noticed this black plastic disc floating on the chain side of the hub. I have 3 pictures. One with it on the hub, one with it in my hands for a close up and one with the hub without it. Is this simply a cover to keep grease in the hub and should have been removed during shipping?

this is my first single speed bike. Is that hub supposed to be open like that?

Thanks for any help

James