Xenophyophores - the giants of the protozoan world Compiled by Dave Walker. How would you answer the question 'What is the world's largest protozoan?'. In freshwater, Stentor can grow to ca. 3mm and Pelomyxa can grow to ca. 5mm, although I've never had the fortune as an amateur pond-dipper to find a specimen of the latter. My concept of the largest is of the order of a few millimetres (see footnote 1), but a news item in 'New Scientist' recently (ref. 1) rapidly changed my view by a factor of twenty - yes, we are talking about 10 cm single-celled 'monsters'!
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