Below are examples of chitons you can find without much effort in northern Oregon’s exposed rocky intertidal. I don’t flip rocks, so these are the just chitons that don’t mind some daylight exposure. Even with this limited set, identification is a challenge for me. I list some of my favorite field guides and identification resources at the bottom of this page. I have relied on them, but any identification errors are mine.
Organization and common names are my choice. I refer to WoRMS for scientific names, and I learn a ton by browsing the natural history riches in Kozloff (1993). All photos are from northern Oregon unless otherwise noted in the caption.
Tonicella, lined chiton
I’m fairly certain these are all T. lineata, but there are other, similar lined chitons, like T. lokii. It’s worth giving any Tonicella you find a close look. They’re common, but you’ll need to pick a good low tide to find them. Lined chitons are variable, but the variation I’ve noticed is much more limited than what you’ll see in some of the guides.
A pair of lined chitons, Tonicella, showing off some color variation 
Look for lined chitons among the crustose corallines. 
Can you tell which direction the head is pointing? 
Tonicella is a beautiful Pacific Northwest chiton 
Tonicella, coming at you 
Maintaining a little open ground
***
Katharina tunicata, black leather chiton
Easy to find and easy to identify, Katharina doesn’t try too hard to hide while it waits out low tide. You’ll find it in the open on low intertidal rocks. In daylight, Katharina will sometimes nose into a shadow. There is individual variation, as seen in the photos below, but you won’t mix it up with any other chiton. I say a few words about Katharina in Black Leather Chiton, Katharina tunicata.
Katharina tunicata, getting a little shelter from sea cabbage, Saccharina sessilis 
Waiting out low tide in a pleasing setting 
Low tide reveals K. tunicata down in the the reds 
And the head is pointing…to the left
***
And the Mopalias…
Until I learn a little more about the group below, the closest I’m going to get is the genus. I think all of these are Mopalia, but even that is an open question. I’m guessing Mopalia kennerleyi is represented below. Mopalia hindsii, M. muscosa, and M. lignosa are all in the running too. Maybe others. If you have thoughts on any of these, please let me know.
Caution, Leptasterias ahead 
Sidling up to Anthopleura 
Sharing wall space with little brown barnacles 
Got a little hitchhiker 
Going the extra mile to blend in 
Up among the acorn barnacles 
Moplia, among the reds, and wearing some 
Nosing in under a lonely mussel 
Keeping it cozy 
Mopalia and a few intertidal neighbors 
Waiting out low tide
References
Gotshall, D. W. 2005. Guide to Marine Invertebrates, Alaska to Baja California. 2nd Edition (Revised). Shoreline Press.
Harbo, R. M. 2011. Whelks to Whales: Coastal Marine Life of the Pacific Northwest. 2nd ed. Harbour Publishing Co.
Kozloff, E. N. 1993. Seashore Life of the Northern Pacific Coast. 3rd ed. University of Washington Press.
Lamb, A. and B. P. Hanby. 2005. Marine Life of the Pacific Northwest. Harbour Publishing.
Sept. J. D. 2009. The Beachcomber’s Guide to Seashore Life in the Pacific Northwest. Revised ed. Harbour Publishing.
Online Resources
Biodiversity of the Central Coast’s Molluscs page is a great starting place
Pacific Northwest Shell Club’s Chiton page
Aaron Baldwin’s Illustrated Keys to the chitons (Polyplacophora)
All the iNaturalist chiton pages are great fun to browse. Here are a few I looked at when I prepared this page:
Northern hairy chiton, Mopalia kennerleyi
This page was updated slightly on April 18, 2020
