Need help identifying a mushroom!

I went to Japan last summer with a tour group.

One of the restaurants had really good miso soup with mushrooms in them.

I really want to know what kind of mushroom it was. I know there aren't many miso soups with any mushrooms.... especially in US... (I'd be lucky if i get both tofu and sea weed... if i order miso soup)

It was really small... around the size of the tofu (maybe slightly bigger)... ?? :?

Also... it'd be great to suggest what kind of mushrooms would go with miso soup...

I think the most common one is nameko, or maybe it was shimeji.

oooo... it looks more like nameko.... thanks!!

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