Where do den den mushi come from? Is it ever explained where the den den mushi come from?

We know there are all kind of den den mushi variating in colors as well in functions. But do they originate from a devil fruit user or are they just some random existing creature in the One piece universe ?
Den den mushi are kind of snails used for visual and audio communication. They are just another type of random creature existing in OPverse which uses telepathic abilities for communication within their own kind.

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