Visian

Visians were an invisible species of predators native to Mira.

Biology
According to the First Doctor, the Visians were about eight feet tall, "vicious", and the only sentient species indigenous to Mira. The pattern of their footprints seemed to indicate that they were bipeds. When exterminated by Daleks they were briefly visible and seemed to have a roughly humanoid form. (TV: The Daleks' Master Plan)

According to the Tenth Doctor, the Visians could not see, as their eyes were invisible as well so could not capture light. Instead, they hunted via smell and sound. The Visians took this to their advantage, shutting out the lights to draw out their prey. (AUDIO: Buying Time)

One account claimed the Visians were capable of speech. Additionally, when made visible (such as when covered in mud), they appeared "thin, bony, with two long, clawed arms, feet like birds' claws, and a narrow head with a beak." (PROSE: Mission to the Unknown)

History
In the year 4000, the Visians attacked the Doctor, Steven Taylor and Sara Kingdom, who had been transported to Mira against their will. They also attacked a group of Daleks who had come to the planet in pursuit of the Doctor. Their combat with the Daleks allowed the Doctor and his companions to escape Mira in a stolen Dalek ship. (TV: The Daleks' Master Plan)

When a Space Security Service spaceship crashed on Mira, Visians attacked and killed the crew save for the android Mark Seven. The Visians subsequently attacked the retrieval team sent to investigate; however, Mark was able to help Anya Kingdom and the Tenth Doctor escape. (AUDIO: Buying Time)