What is the small oval snail

[JamesZ]

A lot of the oval snails on the glass of DT and sump, about 4mm long. Are they pest or sort of snails? Thanks

 

[Alexopora]

A lot of the oval snails on the glass of DT and sump, about 4mm long. Are they pest or sort of snails? Thanks

Judging from this picture alone and looking at how simple its anatomy is, I’d say limpet. Harmless algae grazers that will steadily multiply in your tank as it matures.

 

[JamesZ]

Thank you