You got a very wrong idea of evolution. It is not said that it goes to build more complecated organisms, no, it goes in direction to build more adapted organism, so that quite often means more complecated organism, but it is not a rule, you can cosider that more as a guideline. Quite often organisms loose organs. Humans and apes do not have a tale, monkeys do, does that mean that monkeys are more developed then us human? Parasites got simpler then their ansenstors, Soliter does not have eyes, very primitive neuron system, while worms they involved from did have eyes and more comlecated central neuro system. There are a lot of samples like that. Dolfins do not have legs, they are more primitive then, let's say dogs?