Bill Bryson

.. there is a peculiar group of organisms formally called myxomycetes but more commonly known as slime moulds.

When times are good, they exist as one–celled individuals, much like amoebas.  But when conditions grow tough, they crawl to a central gathering place and become, almost miraculously, a slug ….. Having  hauled itself up to a more favourable locale, the slime mould transforms itself yet  again taking on the form of a plant.. by some curious orderly process the cells reconfigure....... to make a  stalk atop of which forms a bulb known as a fruiting body.  Inside the fruiting body are millions of spores which at the appropriate moment, are released to the wind to blow away to become single celled organisms that can start the process again.

When genetic testing arrived, people in labs were surprised to find that slime moulds were so distinctive and peculiar that they weren't directly related to anything in nature.

There are 5,000 species of bacteria; 26,900 species of algae;  70,000 fungi species; 30,800 amoeba species; plus others, but now that the genome is being mapped more species are being identified all the time.  For example a lot of little organisms that looked like bacteria and behaved like bacteria were actually something else altogether – these are now called Archaea.