Identifying algae

[Harry]

I've got a good grouping of various nerite snails and they keep my glass quite clean. But today, I noticed a certain type of green algae on my seashells. This algae is growing in perfect little circles, about 1/16th to 1/8th inch diameter. The algae is a beautiful bright green, not brown or dingy. And it only appears on the seashells and nowhere else. The Opae do eat it and I'm not worried. Just wondering if anyone is familiar with this. A photo is attached. The spots don't show up that well in the photo, but you can see them. I have three shells in the tank and they all have these.

[achipman]

I have the exact same algae growing, it only grows on my seashells as well. All seems good in my tank and bowls, and I have had this algae for a few months now. So I assume it is just fine, I would like to know what it is as well.

[Stalker]

It's a kind of diatoms. It wont be circular for long.