I would look up fireworms for distinct differences, but it seems that they are generally fatter, and where the bristles are, there are 20,30,40 of them, not just 1, or what looks like a leg.
If the bristles look like little paint brushes, handle with care and remove.
It's a common bristle worm; beneficial detritus eaters in our opinion. We rarely see the classic fireworm, those are frequent in the Keys, brighter color and fuzzier.
The other image appears to be a chiton. Another good hiker.