Frog

Frogs were amphibious creatures native to Earth. The word was also an epithet typically hurled by the British against the French.

Earth frogs
When the Axons offered axonite to the people of Earth, they used it to make a frog grow in size, demonstrating how it could be used to solve world hunger. (TV: The Claws of Axos)

Other frogs
On Monarch's ship, frogs were used for their poison by the Monarch. The poison had the power to shrink living people. (TV: Four to Doomsday)

Josiah W. Dogbolter was half-frog, half-man. (DWM: The Moderator)

On an unnamed planet, the First Doctor, John and Gillian met a race of hat-wearing talking frog people and helped them catch a shark that was trying to eat them. The frog people helped them search for the the TARDIS when it disappeared. (COMIC: Shark Bait)

On the planet Chloris, the Fourth Doctor suggested that a giant frog was responsible for laying a giant egg there. (TV: The Creature from the Pit)

As epithet
The word "frog" was also a somewhat insulting word for "a person from France". It was an epithet typically used by the British. For instance, lighthouse keeper Reuben once thought "the Frogs" might be spying on the British. (TV: Horror of Fang Rock)