Quill (species)
The Quill were a species of humanoids that lived on Rhodia. The Quill lived on the smallest of the southern continents.
Biology
The one Quill known to have visited Earth, Miss Quill, was outwardly indistinguishable from humans.
They possibly had a more alien appearance originally, although it isn't clear whether that is their true form or simply one imagined by April Maclean when picturing the fall of Rhodia: As their name suggests, in that form the Quill sported long quills or spines on their bodies, which sprouted from at least their heads and shoulders. Their skin was primarily reddish brown, with black, zigzagging stripes, and pale white on the lower part of the face.
History
According to Charlie, prince of the Rhodians, they mismanaged their economy, and grew resentful of the Rhodians' success. Miss Quill added, though, that the Rhodians ate up all of the planet's resources, leaving them with little to work with. The Rhodians did their best to help, but in the process made them so dependent that they could never recover.
The two species were eventually at war with each other. The Rhodians won. The punishment they received was considered cruel by Miss Quill, but Charlie found it just: they released a creature into their brains called an arn, which, once it dug itself in, would telepathically link the host to a particular Rhodian, and force them to become their effective slave.
If I use a weapon other than my own hands, the arn kills me, yet if I fail to protect you, I am also killed. If I try to remove the arn, dead again. Slavery!
While they were busy fighting amongst themselves, the Shadow Kin arrived, and killed everyone, Quill and Rhodian alike. All but one of the Quill were destroyed by the Shadow Kin: a female known as Miss Quill once brought by the Twelfth Doctor to Coal Hill Academy. (TV: For Tonight We Might Die)