I found it too, its not the model used by the game. There's also a critter model named Zurkan Giant Eel that looks just like this one but its purple (even more magical). Now the important question is: what is it good for? I've been unable to give it a use in my mod.
i don't know if this have relation, but i think that on development nydus worm was planned to be an "underground transport" instead of classic (and actual) "instant teleport". you could see it jump between platforms on space maps xD
probably this model came from there
Go into data, make a new doodad or unit, go into the "Art: Model" right click and select modify value, and hit "N", (That should bring you to models biginning with N) and look for "Nydus Worm"
Perhaps make it into a unit or something? I dunno, I don't make units.
This explains it very well. :P