Wurm

Told in the Tale of Wurms, wurms are to all unknown creatures that could resemble any kind of creature or not at all. It is said the wurms were capable of producing some sort of super fertilizer which caused the ancient trees of Kelt to grow so high. Unfortunately if the wurms were real the ancient figure Mannimulus took all of them with him into the null area between Middleworld and the Underdark.
The wurms can be found in the name of the druid circle the Wurmsworn who truly believe in the return of the wurms with the barrier gone. Whether this is true is up for debate.