The world’s simplest known animal is so poorly understood that it doesn’t even have a common name. Formally called Trichoplax adhaerens for the way it adheres to glassware, the amorphous blob isn’t much to look at. At just a few millimeters across, the creature resembles a squashed sandwich in which the top layer protects, the bottom layer crawls, and the slimy stuffing sticks it all together. With no organs and just a handful of cell types, the most interesting thing about T. adhaerens might just be how stunningly boring it is.
“I was fascinated when I first heard about this thing because it has no real defined body,” said Michael Eitel, an evolutionary biologist at the Ludwig Maximilian University in Germany. “There’s no mouth, there’s no back, no nerve cells, nothing.”
But after spending four years painstakingly reconstructing the blob’s genome, Eitel might know more about the organism than anyone else on the planet. In particular, he has looked closely enough at its genetic code to learn what visual inspections failed to reveal. The variety of creature that biologists have long called T. adhaerens is really at least two, and perhaps as many as a dozen, anatomically identical but genetically distinct “cryptic species” of animals. The discovery sets a precedent for taxonomy, the science of naming organisms, as the first time a new animal genus has been defined not by appearance, but by pure genetics.
The modern taxonomic system, little changed since Carl Linnaeus laid it out in the 1750s, attempts to chop the sprawling tree of life into seven tidy levels that grant every species a unique label. The two-part scientific name (such as Homo sapiens) represents the tail end of a branching path through this tree, starting from the thickest limbs, the kingdoms, and ending at the finest twigs, the genus (Homo) and then the species (sapiens). The path tells you everything there is to know about the organism’s relationship to other groups of creatures, at least in theory. [Continue reading…]