A Serpentile was a genetically engineered race that the Seventh Doctor created when under the influence of Renk Van Magnastein as part of making Arviem 2 a big theme bar. They were amphibian creatures that quickly matured from birth to adulthood within minutes. This confused both the Doctor and Bernice Summerfield when a frog that leapt of with the Doctor's jacket was worn by a creature.
They were the indigenous species on Arviem 2 with their creation myth being that they were sneezed into existence by a pink dragon, which turned out to be true when Benny found the skeleton of their creator, which was part of Renk's bar. They were engineered to make cocktails and be bar staff. (AUDIO: The Revolution)