The Gelth were a humanoid species who lost their bodies in the Time War. Though they originally had biological bodies, the Gelth were eventually reduced to a gaseous form during the Time War, after their bodies were destroyed during the conflict. They could shape this gas into a wraith-like form, but they needed to be in a gaseous environment to survive
The show's been on forever. Some species names are simply going to get reused. One of the most obvious are the Vogans. Most fans remember the Vogan from season 12's Revenge of the Cybermen. But there's also the Vogans that plagued the Third Doctor…
The top-level category for species is category:species. We know what you're thinking: "Why did we make it to difficult to figure out?" Well, the admin staff of this wiki delight in making things as hard to figure out as possible. .
If you like alien species that are based on Earth animals, you're in luck. All you have to do is go to the page of an Earth mammal and check out the "looks like" box. For instance, if you wanna know what aliens look like elephants, just go that pachyderm's page and find yourself a breadcrumb at the top of the page.
One of the cooler species categories is species by biology. Take a gander! That category will help you find species by the special biology they have. Aquatic species, energy beings, species with binary vascular systems — they're all here waiting for you.
Maybe no publication has been so active in the creation of off-the-wall species than Doctor Who Adventures. Some of the funkiest names in DWU history come from that mag. Both Homozillians and Hussuloofian come from DWA – and we've not even looked outside the hs.