Written by Jonathan Wojcik

   Discovered in 1883, the enigmatic Placozoa (literally "flat animals") are a distinct phylum of animal life with only a single recognized species, Trichoplax adhaerens, though there seem to be a number of different species indistinguishable above the genetic level. They seem to be almost nothing but tiny, featureless scraps of living flesh, but there's a little more to them than meets the eye.

   While a Placozoan has no front, back, left or right, its "top" and "bottom" surfaces differ in an extremely bizarre manner: each side has its own method of feeding. The lower side, which bears denser cilia for walking, encloses food particles and releases digestive enzymes, essentially forming into a temporary external stomach. The upper side, however, is able to prey on single-celled organisms by trapping them in a layer of slime and pulling them through the spaces between its cells, right into the animal's fluid interior. It would be as if you could unzip your stomach and simply place your meals inside.

   Genome sequencing suggests that these mobile smears of life-stuff have been sliming around our seas for quite some time, and have more in common with rest of us animals than you might expect; all the genes necessary for a more complex body and nervous system seem to be there - and in a similar order to us humans - but the little guys just haven't needed them and don't express them. They've got all the windows software, but they're still only working in DOS... and it's served them well.