Scientists say they have found 13,000 new things living in the world's seas that they didn't know lived there.
They're in the middle of a huge project to try and find out about every single thing that lives in the sea.
The survey, called the Census of Marine Life (COML), will cost around £1bn and will take 10 years to finish.
So far the COML has recorded around 38,000 different species, even though results from some parts of the world's oceans haven't been finished yet.
Thousands of species live in the oceans
The results of the survey could be really important in the future as they may offer clues about how to look after things living in the sea.
One of the top scientists working on the project, Dr Ron O'Dor, said: "We're just skimming the surface.
"We know something about the first 100m at this point but we know almost nothing about what lies down in the deep."