Bivalves

Below are examples of bivalves you will likely run across if you spend time on Oregon’s exposed shores. At the bottom of the page, I list some of my favorite field guides and identification resources that should help if you want to take things a little farther. My organization follows Lamb and Hanby (2005). 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 noted in the caption. Some examples below, like California mussels, Mytilus californianus, live on intertidal rocks. Some, like Pacific razor clams, Siliqua patula, are abundant on beaches. Others don’t live on the exposed coast, but their shells wash up there. Gaper clams, Tresus, are an example.

Mytilus californianus, California mussel

The mussel beds of the exposed coast’s intertidal rocks are a joy. Here are looks at a few of the many sides of California musselsYou’ll find more images and a few words about M. californianus at The Curves and Colors of California Mussels.

Adula, date mussel, pea pod
These are probably Adula californiensis. Empty shells washed up on the beach are all I’ve seen.

Chlamys hastata, spiny pink scallop
Mostly subtidal, the few I’ve encountered have been shells washed up on sandy beaches.

Crassadoma gigantea, rock scallop
I haven’t seen live rock scallops in the intertidal. However, shells are not too uncommon in the drift. Kozloff says the right-hand valve is attached, so I imagine the ones shown here are the free left valve.

Magallana gigas, Pacific oyster
Introduced, I’ve only seen them on the protected shores of the San Juan and Gulf Islands.

Pododesmus macroschisma, green false-jingle
I haven’t run into live false-jingles, but it’s not too uncommon to find small empty shells (this one’s about 2.5 cm in its long dimension) washed up on the beach.

Clinocardium nuttallii, heart cockle
Empty shells and shell fragments, such as the ones shown here, are common on exposed surf-swept beaches. However, in life, heart cockles prefer bays, eelgrass beds, and other quiet intertidal and subtidal settings. Therefore, any heart cockle shells you find on exposed beaches have drifted from different ecosystems.

Tresus capax, fat gaper
Fat gapers are likely to be the biggest clam you’ll come across in the Pacific Northwest. On exposed beaches, bleached shells can be abundant, especially near bays with good clam beds. Another less commonly encountered gaper in our area is, Tresus nuttallii, but we’ve never crossed paths. Fat gapers are featured in Getting to Know Gapers, and Have I Shown You My Chondrophore Collection?

Siliqua patula, Pacific razor clam
Bleached shells are abundant on most northern Oregon beaches.

Tellins or Tellens
I have always assumed any relatively large tellin I find is Megangulus bodegensis, the Bodega tellin. There are several species of tellins occupying various habitats, but Bodegas are considered bay clams in most accounts I’ve read. Kozloff says their habitat is clean sand at the mouth of bays that open onto the exposed coast.

Macomas
Any macoma I’ve found on exposed beaches has been a a drifted shell. There are lots of species. Some are bay clams and others live on exposed sandy shores with pounding surf. I haven’t tried my hand at identifying macomas, so I’ll leave it at that. The drifted shells are usually completely bleached, and not too common on my home beaches.

Nuttallia obscurata, purple varnish clam
In northern Oregon, this introduced clam is a bay clam. Any shells you find on exposed beaches have drifted there, or humans have carried them.

Saxidomus, butter clams
Those shown here are probably S. gigantea. I’ve always thought of butter clams in northern Oregon as bay clams. However, they also occur in sheltered Salish Sea waters, where I took some of the images below. Butter clams are large, like gapers, but they lack chondrophores; you won’t confuse the two.

Leukoma staminea, Pacific littleneck clam
Sometimes thought of as bay clams, littlenecks can also be found in other sheltered settings, even on the exposed coast, as the two below were. However, unless you dig a little, you’ll probably only find drifted shells.

Mya arenaria, soft-shelled clam
In northern Oregon, soft-shells are bay clams. Any shells you find on exposed beaches have drifted there, or humans have carried them.

Penitella penita, flat-tip piddock
Shells can be abundant on beaches near sediments suitable for burrowing. I wrote a little about flat-tips in Flat-tip Piddock, Penitella penita.

Boring clams and their workings
I’m not sure what these borers are. If you know, please drop me a line. Borings, when numerous, can transform a landscape. I wrote a little about that in Boring Clams Lend an Otherworldly Appearance to a Miocene Shelf. Many a beach walker has come across a piece of shale riddled by boring clam workings. These are frequently dragged ashore in bull kelp holdfasts.


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

Netarts Bay Today’s mollusks page.

Biodiversity of the Central Coast’s molluscs page.


This page was updated on July 25, 2022