>>>There's nothing magical or even optimal about 2 legs and 2 arms, and arthropods find 6, 8, or many limbs work well. I could do with extra arms now and then.

This is a very old game in science fiction and I love to play it.

Imagine an Arthropod or octapus evolving to the point that he could build a space ship.

His kind would have to develop metallurgy, he's need a brain big enough for Einsteinian physics and beyond. He would need to be a tool user. He couldn't even wield a hammer with lobster claws. Is refining of metal and alloy creation even possible under water?