Can anyone identify these things?

[willsmithpro12]

Help me id these things, they are stuck to the glass but easy to remove. The blue-tinted photo is in the tank on the back wall and the white-tinted is one of them removed from the tank, any help you can provide would be great.

 

[ISpeakForTheSeas]

Limpets of some variety - most are harmless/beneficial algae eaters.

 

[willsmithpro12]

Thank goodness, finally not a pest

 

[CoralB]

Limpet would be my guess as well