Prypiatosian-A

Prypiatosian-As are an unseen race of aliens from Prypiatos, a highly-irradiated planet in the Andromeda Galaxy.

Biology
It is currently unknown what Prypiatosian-As look like, but it is very likely that they are sapient lifeforms.

Culture and society
Prypiatosian-As live in subterranean cities that have been lead-lined for their own protection from the hazardously irradiated world that had once been their home.

History
Prypiatos was once the marvel of the Andromeda Galaxy, with mega-cities filling entire continents with hundreds of thousands of glittering structures that truly seemed to scrape the sky, but an atomic war put an end to that.

In the aftermath, some of the planet's denizens managed to escape underground to avoid the nuclear fallout. In time, they eventually established a new subterranean civilization of their own, becoming the Prypiatosian-As.