Oh, what bug is this?

[Sebastiancrab]

These bugs come out only at night on the side glass. The have a solid hard back. Any idea what they are?

 

[EeyoreIsMySpiritAnimal]

Impossible to tell from your picture... Could be spirobids, collonistas, chiton, limpets...

 

[WheatToast]

Impossible to tell from your picture... Could be spirobids, collonistas, chiton, limpets...

+1. Microscope pictures would be great.
Ostracods are another possibility.

 

[Sebastiancrab]

+1. Microscope pictures would be great.
Ostracods are another possibility.

It might be ostracods. I will try to take closer pictures.