Not that the animals found in Riven can also be found on Earth. One is a useful, froglike creature (in-house name: ytram).
The origin of the ytram deserves its own paragraph. In the first days after Richard arrived at Cyan, when Chris Brandkamp's garage was still serving as world headquarters, there was an annoying frog living behind the drywall next to Richard's desk. Also, there were constant phone calls from a guy named Marty O'Donnell, who kept bugging the Millers about doing sound effects for Riven. He was a nice guy and all; he was also a pest. So when the guys were searching for a convenient name to call Riven's not-frogs, Richard suggested ytram, which is Marty backward. Marty knows about all this and thinks it's funny; says he does, anyway. PS: He got the job.