What are these???

[TJeep_1999]

I found these under my waterfall rocks. I thought it was small snails at first as they are very hard, but I'm thinking it might be some type of cocoon or something once I got a closer look. They are very small like 1/16" by 3/16". What are they? Should I be concerned?

 

[bagsmom]

I don't know what they are but I remember doing a ranger walk in a national park - focused on rivers and streams. The ranger showed similar casings on some rocks and said they were an important part of the ecosystem. My best guess is that you have a very healthy pond and that whoever hatches out will be a welcome resident!