When it comes to intertidal close ups Pollicipes are agreeable subjects. They won’t much change their demeanor if, to get things right, you need to nestle in among them.
Gooseneck barnacles, Pollicipes polymerus, stick to surf-swept shores. They stand out in the the mussels beds.
theoutershores 
Last week I saw their shells for the first time in seagull regurgitation.
Oh fun observation! The first time or two I saw it, I didn’t recognize the shells for what they were. I hate to admit it, but I thought they might be shells from a small intertidal bivalve I wasn’t familiar with. I figured it out only when I started noticing somewhat complete barnacles also regurgitated. Sounds like you had it figured out right off the bat. Thanks for sending this comment, thinking back on my own experience gave me a smile.