Cantankeri are a species of "fish" (isopod) that incubate inside asteroids of the High Wilderness, growing into their surrounding rock. This species is a safety hazard for travelers, especially in the mining industry, but has some use as a source of food or precious stones. Their grunts are characterized by humans as sounding thoroughly disgusted by their surroundings, and that attitude is backed by their hostility to any spacecraft or sky-beast.
Folk tales insist that the home world of the cantankeri was destroyed in an ancient time, which they are nostalgic for. If so, that would mean that practically no cantankeri have been born in the centuries afterwards, and they are being killed by at a rate that completely outpaces their reproduction, assuming that the conditions necessary for their reproduction even exist.
Especially thick shelled cantankeri are called "bulls", and have a worse attitude than other members of their species. Their age befouls their innards, but those same innards often carry valuable deposits of solidified time. It's also common for cantankeri to become the propulsion for large growths of cosmogone fungus.