Did you buy one and now there's that many? I'm rolling with Aiptasia. Regular anemones don't reproduce like that. There's lots of species and I've seen some odd, non-traditional looking ones over the years.
There are a lot of different types of Aiptasia, they do not all look identical to Glass Anemones.
I would be concerned if they are a pest anemone, which they appear to be. If it were my tank I would remove them.