Textures!
Fantastic use of bump maps here. Did you make all the textures yourself, including the ground? And I like the purple highlights, although its not clear whether it is a reflection or some kind of bio-luminescence. (That is, did you put a purple light somewhere, or do the textures glow purple?) My one and only negative comment is that I expect slugs to be slimy, but for all I know you wanted these to look dry and only semi-organic.