Researchers found a new species in the waters off of the U.K. — but they didn't realize it at first

A new species of sea slug has been discovered off the waters of the U.K. Researchers with Centre for the Environment, Food and Aquaculture Science said they originally thought it was a well-known species, Pleurobranchaea meckeli, found near Spain and the Mediterranean Sea – but they weren't sure.

There were no previous records of this type of slug in the U.K., "raising questions around its identity," the center said in a news release. 

The new species of slug, which has been named Pleurobranchaea britannica, is between two and five centimeters long – less than two inches and has gills on its side. It was discovered during a routine survey of sea life in southwest England and the center searched for experts who specialized in this type of slug to help them identify it.