These definitions don't work for meiofauna, the team—including a biologist, a mathematician and a physicist from different U.K. institutions—argues. For example, other studies have tried to distinguish meiofauna species by taking a whole bunch of them, sieving them for size, and then sequencing a part of their genes. Scientists then map out which individuals are more related to each other, based on their genes. Individuals of all the same species should kind of clump together on a map. Meiofauna gene-relatedness maps, however, have individuals scattered all over them, with no clear species clumps.