Re:Some solutions missing. (Score 1)

There are certainly plenty of single-celled critters and even some larger parasites that use the screw as a means of locomotion. The wheel is a whole different problem. In order for it to work it has to be totally detached from its axle. That makes minor things like circulation, nerve transfer etc. rather difficult. Topologically, life forms tend to be of order one - donuts with skin on the outside and some form of digestive system on the inside. I think it's safe to say that there are NO known organisms that consist of two wholly independent parts (Master/slave relationships don't count!). /hazard..