I looked "chiton" up on Google Image Search. This is not a chiton. It almost looks like some kind of bloated sand-dollar given the distinct five-pointed ridges across its dorsal surface. That, plus the bulky arm-like processes that attach to the rock surface, makes me think it's an echinoderm. It's the strangest creature I've seen on the island so far. Today I saw an anole lizard scamper across a rock, two small white herons, and sandpiper. We traveled to a really beautiful part of the island called "Needle Rock," and I was horrified to realize that I'd forgotten my camera. We'll probably go back with camera in tow, because you guys really need to see this formation.
Maui, for those who haven't been here, is kind of like Racoon City--the walking dead parol every street and every shopping center. This is like a rich (old) man's Florida. Tomorrow, snorkeling, and I bought a waterproof camera specifically for such adventures!