ID ??? Very weird looking thing

[C.Eymann]

Roughly the size of a dime.

 

[hotelbravo]

Amphiscolops? Clear flatworm. Yours looks a little to round but If that is what it is then it is harmless.

Thats my best guess

 

[Sugar Magnolia]

Looks like a little jellyfish.

 

[Bongo Shrimp]

I had these in a tank last year. IDK what they are but that's as big as they get, and they don't move right? If you look closely and tap the glass or disturb them you'll notice it's a little strange bivalve.

 

[Betta132]

It looks almost like a very strange limpet.
Can you touch it and see if it's soft or hard? Does it do anything? Does it respond to stimulus, and how so?