You've made a circular definition. And I wasn't claiming that only nerve cells can form intelligence, but I think that if we expand the definition beyond what people normally call intelligent, then we should be more precise than the vague "ability to achieve goals in a wide range of environments" or else every complex adaptive system would be called intelligent, in which case we can drop that name because we already have one: complex adaptive systems (https://en.wikipedia.org/wiki/Complex_adaptive_system)