A group of researchers in Japan say they have discovered a new variety of shrimp-like creatures called Gammaridea in the mouth of a whale shark.
Gammaridea are a type of crustacean, a group which also includes water fleas.
They have been found in various environments such as the deep sea floor and mountains several thousand meters high.
The new variety found by the team led by Hiroshima University Associate Professor Ko Tomikawa is about 5 millimeters long and has hairy legs.
The researchers say it appears to enter the mouth of a whale shark along with plankton and settle there, feeding on organic substances that flow in.
They suspect the mouth of the whale shark, the largest known fish species, provides a safe environment from predators.
The group says only some parasites are known to live in the mouths of other species.