Omissus is a variant of the European herring gull. It is largely similar to a common herring gull, but unlike the common species, it has yellow legs.
There is very little research and documentation about the omissus variant, some authors believe that it may be a species of its own.
Omissus can be confused with the yellow-legged gull, but the omissus does not have as distinctly bright yellow legs as the yellow-legged gull.
Omissus was first described in 1928 by the Russian ornithologist Theodor Pleske