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I've heard it claimed that the nummulite was the largest (by volume) single-celled organism known. Is this still considered true? --Iustinus 09:06, 8 September 2006 (UTC)
This site  claims an alga, Caulerpa, is single-celled and grows to a meter; this one  has some other ideas for things up to 25 cm. Geologyguy 14:23, 8 September 2006 (UTC)
HA! Funny you should mention that, given that a few hours later I was asking about Caulerpa on my blog. But since Caulerpa is colonial and coenonytic I'm not sure it counts. I havent' read that second site you linked to yet, but it looks very promising, so thanks! --Iustinus 17:15, 8 September 2006 (UTC)