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Someone must have gotten a shippment of these because a couple people have asked about them. They are mini-anemones. They ususally ship at sizes between 1cm-3cm. Very small. Their attraction is that when they split the new anemone might be a different color and then becoming a colony. I think they are too small to hurt anything unless like the capt said it crawls in its mouth.
They're going for a pound (1L) on eBay in the UK. I think they may be the local UK variety which are a cold water intertidal species. Not necesarily the best animal for a tropical tank.