The Thalatth was a species with a complex lifecycle. They began as seed pods capable of travelling long distances through space in search of water, and turned into huge, multi-limbed, savage, purple carnivores with two eyestalks. Ultraviolet rays from a sun took the creature through a chrysalis stage to emerge in its final form as a beautiful winged creature, literally made of stardust. This final stage of the Thalatth was better known as a Solarix Prizmatterfly.
When one landed on Earth, it was collected by the research ship Deep Ocean 7, which was collecting stock for the Deep Ocean's fully functioning experimental biosphere at Las Vegas. The Thalatth feasted on the food stocks in the tanks before breaking free from the tank. It was lured into the desert by the Tenth Doctor and Heather, using whale sounds. In the sun's rays, the Thalatth completed its life-cycle and left the Earth as a Solarix Prizmatterfly. (COMIC: Hook, Line and Sinker)