I can answer a couple of the questions.
eyes: yes, like pea-brain pointed out, the information is processed before it actually hits the brain. I believe this is done in the eye stalks. Our brains on the other hand gets raw data and must process it.
they're closest realtives are lobsters i belive.
mouth: I assume it's the same mandible kinda mouth as a crab or most other crustaceans.
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