What is growing on my amazon sword?

[Gowalkitoff]

I noticed these today growing on my Amazon sword.  I don't see any on my other one or other plants.  White, 3d, biggest is about an 1/8" oval.  Black center.  Freshwater setup with one jaguar cichlid and one jack dempsey.  No new additions, changes, snails plants, etc.

[lucius]

They may be freshwater limpets.

[Gowalkitoff]

Oh interesting, thanks!  I wonder how in the world I ended up with them