Jupiter

Jovian Camelephants are easily stampeded. (Adventure 327)

On Jupiter, rainbows between the moons are considered unlucky. (Adventure 343)

Given the fact that Jupiter's surface is uninhabitable, there are two possibilities: 1. This actually refers to one of Jupiter's major moons, from which the other moons would visible in the sky under certain circumstances, 2. This refers to some sort of artificial settlements floating in the upper atmosphere of Jupiter. Due to the astronomical situation pictured, I favor #2.

The two-trunked Jovian Mastodon is one of the galaxy's fiercest beasts. (Adventure 358)