The scuttlers were a species that evolved on an unknown planet in the Milky Way. They had the ability to literally swap body parts with other members of their species, and despised uniformity and duplication. This unique feature of their biology -- and racial psychology -- made them introverted, as they found no other species like themselves. With few contacts with the greater galaxy, and no pressing need or desire to explore, they remained -- unintentionally -- concealed from the Inhibitors for millions of years.
They preferred cold planets, usually orbiting gas giants, and possessed a few hundred colonies at the peak of their civilization. When the Inhibitors found them, however, they were put on the path to extinction. In the end, it was the Nestbuilders that ended them, cutting short their negotiations with the shadows before they could allow them to cross between universes.