The Wibliwee were a race of something like intelligent bacteria. They were, at least according to one ship's crew, incredibly advanced and nearly immortal. Their ships were slightly bigger than a human's palm.
A ship of Wibliwee had a reaction core accident and became stranded on Earth after it had been attacked by Pararachnids. The Wibliwee were trapped in the Line underground for seventy years before finally making contact with one of the mostly unconscious humans, named Kimo Ani. They convinced him to bring their ship to the surface. He encountered the Sixth Doctor and Peri, but was terrified and threw the ship. Peri took it up, and all three were forced to run away as several Pararachnids had shown up. Peri and the Wibliwee were captured by Monitors and brought back underground.
When Peri was attached to the Line, the Wibliwee expected to have to wait several more decades for escape. However, the Doctor and Kimo Ani had escaped from the Pararachnids, and after they saved the humans from more Pararachnids, the Wibliwee and the Doctor engaged in mutual trade to help repair their respective ships. The Wibliwee finally left Earth. (PROSE: Moon Graffiti)