[abeppu]

I wouldn't say "suspicious", but I do think it's interesting. Yes, it needs to receive light, but any exposed part of the animal could do that. Does it "feel" to the animal like it's part of vision, in the way that we experience taste in an integrated way combining signals from taste and smell receptors? Does pairing with vision make it easier to process both together for navigation? That is, you're point is how a separate organ would make it like an independent sense; is it functionally beneficial for it to not be independent?