How much is written up

All 756,338 species in this edition have a page and can be searched for. 250,258 of them — 33.1% — have an article written rather than an index entry alone. Here is where the gaps are.

There is a second gap behind this one. Science has described roughly 1.5 million animal species; the taxonomy this edition is built on is drawn from identified observations, so it covers vertebrates almost completely and thins out sharply among the insects, molluscs and worms that are described in the literature but rarely photographed. Where the names come from.

Group by group

The forty largest classes of animal, by how many species science has described in each and how many of those have been written about here.

Which groups get written up first, and why, is set out in the coverage policy.