The race to describe and archive the planet's dwindling biodiversity (see K.-D. B. Dijkstra Nature 533, 172–174; 2016) becomes even more urgent with the realization that the task's scale may be an order of magnitude greater than estimated.
Dijkstra notes that we have so far named only about 1.2 million of Earth's estimated 8.7 million or so eukaryotic species. Such estimates are based largely on counts of invertebrate 'species' that are visually distinguishable ('morphospecies'). However, genetic analysis has revealed that many supposedly uniform morphospecies are complexes of multiple, reproductively isolated lineages, each of which constitutes a separate but cryptic species (D. Bickford et al. Trends Ecol. Evol. 22, 148–155; 2007).
These discoveries boost the biodiversity of even the largest vertebrates, such as elephants. The effect is greater in small vertebrates (such as lizards and frogs) and in invertebrates, which are often complexes of ten or even more species (P. M. Oliver et al. BMC Evol. Biol. 10, 386; 2010). The quoted estimate of the number of (morpho)species on Earth could therefore be just 10% of the true species number.