I think the translation was wrong. It shouldn't have been "a part of his shell". If anything it all, it may be an organ, or his heart, or like a part of his brain or whatever. It may even be a bit.
It being a part of his shell does not necessarily mean that there are more of those on his shell. The game implies that it was special. And it couldn't have made him smarter, since it's something that is inferior to him. The thing itself is a link to him, for others who cannot see him. Like the pentalir or whatever those orbs for communication were in LoTR.
And in turn, the Flame itself has a constant feed of energy from Lavos. This method was used (most likely) in the Mammon Machine, as the flame would drain it, and the dreamstone would harness/channal and amplify it. The reason why Lavos woke up was that the Machine made the Flame suck to much energy, which was un natural for it, and the dreamstone amplified the sucking up action, which made Lavos realise that something was wrong, and caused him to destroy Zeal.