Chitons

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Below are examples of chitons you can find without much effort in northern Oregon’s exposed rocky intertidal. Even with this limited set, identifications are a challenge for me. I list some favorite field guides and online resources at the bottom of this page.

Organization and common names are my choices. 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 noted.

Tonicella
I’m pretty confident these are all lined chitons Tonicella lineata but not entirely so because other, similar Tonicella, like T. lokii, can be encountered (and not just T. lokii; there are others!). Thus it’s worth giving any Tonicella you find a close look. My examples are from the mid to low intertidal, where they are relatively abundant and easy to spot, for which I am grateful because each one is pure living beauty. I offer a photo and a few words about their pattern in Tonicella lineata’s Fine Lines; and I explore the cleaner and the crust in Corallines and Chitons Layer the Lower Intertidal.

Chiton among crustose corallines, articulated corralines, some red blades, and a giant green anemone.
Tonicella is a beautiful Pacific Northwest chiton
A kind of shy looking chiton with its head down, tucked into some articulated corallines, crustose corallines, mussels, a limpet, and surfgrass also make an appearance.
Can you tell which direction its head is pointing?
Featuring a chiton on crustose corallines. Red blades on either side.
Look for lined chitons among the crustose corallines
Closeup on a chiton upside down in a crevice.
Lined chitons don’t mind being upside down
Close in on a chiton that has seemingly cleared a small area of crustose corallines off a vertical surface. The scene also features a sponge and a portion of a giant green anemone.
Maintaining a little open ground
***

Katharina tunicata, Katy chiton
Easy to find and identify, Katies don’t try too hard to hide while they wait out the low tide. (But I feel like sometimes they’ll nose into a shadow.) You’ll be able to find them in the open on mid and low intertidal rocks, and you won’t mix them up with another chiton. I say a few more words about Katharina and show some more photos in Black Leather Chiton, Katharina tunicata, and Tidepool Treat: The Schizymenia – Katharina Connection.

A fairly closeup view of a single black leather or Katy chiton on a bare rock in between blades of sea cabbage.
Katharina tunicata cozying up with the sea cabbage
Waiting out low tide in a pleasing setting
Low tide reveals a Katy down among the reds
And the head is pointing… (Which direction?)
***

And the Mopalias
Until I learn a little more about the group below, the genus is as close as I’m going to get. At the bottom of the page I’ve listed references for some of the Mopalia species you might encounter on the open coast.

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. Accessed 10/01/2022.

Aaron Baldwin’s Illustrated Keys to the chitons (Polyplacophora). Accessed 10/01/2022.

It would also be worth scrolling down to chitons in Common Sea Life of Southeastern Alaska: A field guide by Aaron Baldwin & Paul Norwood. Accessed 10/01/2022.

Cowles, D. (2005). Tonicella lineata (Wood, 1815). Invertebrates of the Salish Sea. Rosario Beach Marine Laboratory. Accessed 10/01/2022.

Lunsford, R. (2002). Katharina tunicata. Invertebrates of the Salish Sea. Rosario Beach Marine Laboratory. Accessed 10/01/2022.

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

Hind’s chiton Mopalia hindsii

Woody chiton Mopalia lignosa

Mossy chiton Mopalia muscosa


I updated this page on November 1, 2022.