WoRMS isn't finished yet. There are an estimated 1 million multi-celled organisms living in the Earth's oceans, and probably about 10,000 of them are sitting in laboratory jars waiting to be identified. Or misidentified, apparently.
Don't panic: Many of these misidentifications are from the days when scientific literature was much less accessible than it is now. WoRMS, which is hosted by the Flanders Marine Institute in Belgium, is trying to make an easy-to-use database of existing species for exactly that reason. Hopefully its work will make "new" species even less likely to sprout from previously identified ones.
According to The Guardian, one species in particular has come out as the most commonly misidentified: a simple, common snail found on the coast of Britain. The rough periwinkle snail, first named Littorina saxatilis in the 1700's, has since been named as a new species another 112 times. This is probably because the species comes in a wide variety of shapes and colors.