Calappidae
Harlequin Shrimp
I doubt anything plastic or more specifically with flow holes would hold them permanently...they slowly chip away at the hole/slit, they have all the time in the world/their life and it almost seems stimulating to them, like how we would watch TV/Playing Video Games/Etc.
Even if it were and inch thick they would slowly chip away at a flow hole/slit inevitably in time making it wide enough to fit through...
That was always my thoughts with glass also, but I'm assuming it's 1 in a thousand in that case.