Just to tell you all that we started a 12-people-project in our faculty using JME2 to build up a Spore related game.
Are you creating the creatures in a modeling tool (e.g Maya, Blender) or dynamically at run-time during the game?
As a beginning we build them out of joints and simple polygonal objects (of course xD).
Later on we will model some creature parts and make them available when creating a creature. We will use Maya.
And the creature will… evolve itself (just the way it moves and the size of some parts of its body) depending of the scenary.
It's more like a simulator… and we are hoping JMonkey will help us.