Are you lost
Don't remember seeing you here before
First, I need some info. You are taking about the long finger like "thing" in the center of the pic. It curves to the right and goes behind the rock. If that is it that is no Chiton at all. Chitons can not bend around corners.
How does this thing move or does it move. Is there a shell, for sure ?
That pic is bad
Why can't you pick it up and put in a dish for a better pic ? Funny on my search I ran into you on another forum but no pics, they have been removed. Some else on another forum has something similar and is using the same ID as you. He has no nics
As your pic sits, as is, it looks like Jacknife, only they are usually not that curved and they are a long curved bivalve and do get 6 " long and are about as wide as your finger and can move around. However, jacknifes, razor usually sit in the sediment
Something else I found;
The most common species of coralline in the region, Hydrolithon onkodes, often forms an intimate relationship with the chiton Cryptoplax larvaeformis. The chiton lives in burrows that it makes in H. onkodes plants, and comes out at night to graze on the surface of the coralline. This combination of grazing and burrowing results in a peculiar growth form (called castles) in H. onkodes in which the coralline produces nearly vertical, irregularly curved lamellae.