While doing the Monouga Feeding Pits/Laboratory quests, the big monouga seems to be spawning in the feeding pit even if you do not ring the bell to summon it from the laboratory. This has been the case when doing both the 80+ and 120+ versions of these quests. The big monouga is not there right away, but is there by the time you run down to the bottom of the dungeon.

The Monouga Feeding Pits/Laboratory quests are listed as "Needs Review" on the Status of Content page so this may be a known issue.