We have come a long way since Lister: 1.7 million species tidily bundled into five kingdoms; a neat summary of earthly life. Now biologists can get on with something useful: biotechnology, a cure for cancer, that sort of thing.
Or so we thought. Last week, Peter Funch and Reinhardt Kristensen from Copenhagen described a new kind of beast that is as different from anything else as, for example, starfish are from ourselves. It was not found in some obscure swamp but attached to the noses of lobsters that are dragged every day from the seas between Denmark and Sweden. The beast is small by everyday measures - a third of a millimetre - but elephantine by the standards of biology: 40 times bigger than the red blood cells which in turn make roomy apartments for malaria parasites. Yet it had been missed. Among its many oddities are the miniature males which cling to their bulbous mates like seaside postcard hubbies. Funch and Kristensen call it Symbion pandora - but this is not simply a new species. It represents a whole new phylum; phyla being the huge ranks of creatures just below the level of the kingdom.
We will have to grow used to such shocks. The known inventory of species must fall short of reality by at least 10-fold, probably more than 20- fold. For example, in the 1970s, Terry Erwin of the Smithsonian Institution in Washington searched exhaustively for beetles in the canopy of one single species of tree in Panamanian rainforest and found no fewer than 1,100 species. About 160 of them, he felt, probably relied more or less exclusively on that particular tree. But tropical forests contain around 50,000 species of tree. If they were all like the one he studied, then there must be 8 million species of beetle alone, just in tropical treetops. Beetles account for a high proportion of all known species: "God," as J B S Haldane observed, "had an inordinate fondness for beetles." If there are 8 million beetles, said Erwin, then the true number of all species must be about 30 million. And indeed the more biologists look the more they find - not just little creatures, either. Simon Bearder of Brookes University, Oxford, studies bushbabies in West Africa and has now found six species where the books said there were two: but the true number, he thinks, probably approaches 40.
We know even less about microbes. The traditional way of finding them was to take a piece of mud or dung or pus, place it in a culture medium, and see what grew. So the world inventory of bacteria is simply a list of what can be grown. Norm Pace of Indiana University in Bloomington is now looking directly for the DNA of bacteria in soil, oceanic mud, hot springs and everywhere else he can think of and finds that the true variety is at least 100 times greater than the number that can be cultivated and therefore has been recognised up to now. The next decade will turn the venerable craft of microbiology on its head.
The interest lies not in the number of species but in the range of living things being discovered - the ways of manifesting life. Microbes make the point spectacularly - but so, too, do the homely animals, although they are much less adventurous. Traditionally, animals have been split peremptorily into "vertebrates", including us and robins and fish; and the "invertebrates", including snails and shrimps and the rest. But it has long been clear that many invertebrates are far more different from each other than many of them are from us. Nowadays, the vertebrates are seen as just one group or phylum of animals among 35 or so - and the other 34 or so are the different kinds of invertebrate. You might have supposed that we at least knew all the phyla - but Symbion has punctured any such complacency. It turned up, as great a novelty as animals can provide, right under our noses.
Yet the animals as a whole represent only a sliver of life's variety. Mitch Sogin at the Marine Biological Laboratory at Woods Hole, Massachusetts, has found that the DNA of animals, plants and fungi is much of a muchness; by the broad standards of life, oak trees are almost the same as us. But many of the "protists" are hugely different; the brown seaweeds (such as kelp); the red seaweeds even more so; various protozoan groups such as the malaria parasite; and so on. The human gut parasite Giardia is distinct from all the rest; its ancestors might have been ploughing their own furrow for a couple of billion years. Indeed if plants, animals and fungi deserve to be called "kingdoms" then a dozen or so other distinct groups among the protists deserve kingdom status, too. It seems that we human beings plus our cats and dogs and other familiar creatures are merely part of one division of one phylum among 35 in the kingdom of animals, which in turn is only one kingdom among 15 or so. In biology as in cosmology: eachdiscovery pushes us and our conceits further towards the periphery.
Yet the greatest revelation of all is due to Carl Woese of the University of Illinois. In the 1970s, he found that the creatures known as "bacteria" represent two enormously different groups. One group he called Eubacteria - now simply called "Bacteria"; the other he called Archaebacteria - now simply "Archaea". Each of these, he said, deserves to be called a "Domain": an even more embracing category than Linnaeus's Kingdoms. The animals, plants, fungi and the huge miscellany of "protists" then form a third domain, the Eukaryota.
So this is life through modern eyes. Since the 1950s, we have leapt a conceptual aeon. We are at least two conceptual aeons ahead of Linnaeus. But the people who are doing the work emphasise how little is known. What we know now is just a glimpse of knowledge to come. Three domains sounds impressive - but there could be a dozen.
Does it matter? For cultural reasons, certainly. It is a shame to partake of life and not know how wonderful it really is. But also for practical reasons - for the broad lesson to emerge is how naive we have been. This, we tell ourselves, is the age of biotechnology, when microbes will take over from industrial chemists. But what microbes? We hardly even begin to know what is out there. We seek cures for cancer and Aids and may indeed find a few but we simply don't know enough biology. The necessary knowledge will come from a broader vision: seeing the number of ways it is possible to be alive, therefore, is literally vital. Symbion is more than a quaint and tiny creature: it is a symbol of what is yet to be found out.
The writer is a visiting research fellow at the centre for philosophy,London School of Economics.