While I only found this article mildly interesting, what I did take from it was the following:

... evolution does not proceed along a straight line, counter to many cartoons. And it's pretty common to find things evolving more than once, DeSalle said.

"You see that in other systems and kinds of anatomy — dorsal-ventral polarity in animals, which means having a stomach and back, has evolved twice. It's different in invertebrates and vertebrates. Even if you flip the things upside down, in other words, they are not the same," he said.

And the eye is another example, he said. "They are incredibly complex things, but they have evolved many times," he said. The famous biologist Ernst Mayr once wrote a paper stating that the eye had evolved 25 different times in nature...

How cool is that!

Of course things can evolve more than once, it only makes sense. Especially if there's DNA coded for it all over the place. But that's not something you really think about, until you see or hear it.

From earlier in the article:

"Placozoans and sponges both have genes for nervous systems in their genomes," he said.

But they don't have nervous systems, at least that we can detect. They haven't evolved one yet.