I for my part have also a SF setting with many sentient species, including humans, pterodactyloids, giant sentient bears ans animals with a pentaradial symmetry, like echinoderms. The "echinoderms"' planet have a natural nuclear reactor, like Oklo 2 billion years ago on Earth, and it is a radioactive place, so people are afraid to go there (they have a technology level roughly like Middle Ages, so all they know is that people who go there can get sick and die either because of the radiation or several years after because of cancers (well they don't know it's cancer but...). And if they don't die, their children have malformations).