The Lemuria (Pangea in Japan) was the Cybertronian ship that brought the first transformers and Cyber Planet Key to Gigantion. After battle with the inhabitants of Planet X, the Lemuria was built into a city at the center of the planet, where the Cyber Planet Key lay. After the Cyber Planet Keys and the Omega Lock were stolen by Galvatron, the Lemuria's engines were activated and it was used by the Autobots in an effort to create a new spacebridge between the alternate universe and the Cybertron universe. Though this effort failed, the sacrifice of Vector Prime reopened the interdimensional portal, allowing the Lemuria to accompany the Ogygia and the Atlantis back to its home universe. Combining with them and the Hyperborea, the Lemuria became part of the Ark, which Primus used to close the black hole.
In the final episode of Transformers: Cybertron, Optimus Prime (Galaxy Convoy) proposed a new Space Bridge project using the power of the four Cyber Planet Keys and the four great Cybertronian ships. Many Autobots and former Decepticons joined in the project. Metroplex led the Lemuria and Gigantia Cyber Planet Key with Drillbit, Signal Lancer and Brimstone under his command.
Read more about this topic: Spaceships In Transformers: Cybertron, Transformers: Cybertron