Bivalves

Below are a few examples of bivalves that live on Oregon’s exposed shores or their shells that have washed ashore there. Some, like California mussels Mytilus californianus, live on intertidal rocks, while others, like Pacific razor clams Siliqua patula, are abundant in beach sand. Other bivalves shown don’t live on the exposed coast, but we see them because their empty shells wash ashore after lives led in sister ecosystems. Gaper clams Tresus are an excellent example of that. These are the easy-to-spot bivalves I’ve seen and photographed on the shores I’ve visited. 

Regarding live clams in their shells, my set is limited. I try to keep my touch light by not turning rocks or digging, so most of the shells I show are empty and drifted. If I offer an image of a live bivalve disturbed by me or someone else, I note it. Organization-wise, I loosely follow Lamb and Hanby (2005). If I use common names, they’re my choice. Experts cover the bivalves shown below and many more in the books, field guides, and identification resources listed at the bottom of this page. My photos are from northern Oregon unless noted.


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 mussels. You’ll find more images and a few words about M. californianus at The Curves and Colors of California Mussels.

Deep in the heart of the mussel bed
A homogenous, medium distance shot of mussels encrusted with barnacles, mostly thatched and a few acorn
It’s common for California mussels to be encrusted with barnacles
California mussels , exposed at low tide, perched on a vertical rock wall
California mussels can handle full sun at low tide and pounding surf at high tide
Intimate shot with concentric growth curves and and black, orange and blue coloration
When not too heavily encrusted, California mussels show off beautiful curves and colors
Empty mussel, both valves still connected, on sand
Shells that are strong enough to withstand the surf hold up well in the drift line
***


Adula Date mussel, Pea pod

These are probably Adula californiensis. Empty shells can be abundant on beaches near sediments suitable for burrowing.

A shell over 2 inches (5 cm) long is on the big side | Central Oregon
The Periostracum is hairy on one end and eroded on the other | Central Oregon
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Chlamys

Empty and drifted scallop shells Chlamys occasionally wash up on surf-swept beaches. I’ve always assumed the examples shown here are spiny pinks C. hastata, but I’m not certain about that. (It’s a call for experts.) Either way, they can be a spot of color and delicate beauty on the beach.

Closeup of an empty and drifted pink scallop Chlamys shell, just one valve, resting on the sand in the swash zone. Exterior surface exposed.
An empty drifted Chlamys valve resting on the sand. Exterior surface exposed.
An empty drifted Chlamys valve resting on the sand. Exterior surface exposed.
An empty drifted Chlamys valve resting on the sand. Exterior surface exposed. A few tiny Velella velella stuck to the shell.
An empty drifted Chlamys valve resting on the sand. Exterior surface exposed.


I flipped this shell over to expose its interior surface.

An empty drifted Chlamys valve resting on the sand. Exterior surface exposed.
An empty drifted Chlamys valve resting on the sand. The shell has been turned over to expose the interior surface.


Every once in a while, a drifted shell stained dark will turn up.

An empty drifted Chlamys valve resting on the sand. Interior surface exposed.
As I found it
An empty drifted Chlamys valve resting on the sand. The shell has been cleaned off and turned over to expose the exterior surface.
Cleaned up and flipped over
***


Crassadoma gigantea Rock Scallop

Drifted unattached valves, which I’m guessing are left valves (Kozloff says the right valve is attached), are not too uncommon in the drift. The exterior surface of older shells are pitted from the erosive forces of encrusting boring sponges and other encrusting and boring organisms.

An empty and drifted rock scallop Crassadoma gigantea shell, just one valve, resting on the sand. Exterior surface exposed.
An empty and drifted rock scallop Crassadoma gigantea shell, just one valve, resting on the sand. Exterior surface exposed.
An empty and drifted rock scallop Crassadoma gigantea shell, just one valve, resting on the sand. Interior surface exposed.
An empty and drifted rock scallop Crassadoma gigantea shell, just one valve, resting on the sand. Exterior surface exposed.
An empty and drifted rock scallop Crassadoma gigantea shell, just one valve, resting on the sand. Interior surface exposed.


Smaller, presumably younger, examples with less exterior shell erosion. On the interior, the purple coloration at the hinge is a constant.

An empty and drifted rock scallop Crassadoma gigantea shell, just one valve, resting on the sand. Exterior surface exposed.
From the central Oregon shore
An empty and drifted rock scallop Crassadoma gigantea shell, just one valve, resting on the sand. Exterior surface exposed.
An empty and drifted rock scallop Crassadoma gigantea shell, just one valve, resting on the sand. Interior surface exposed.


The purple color is pretty amazing. It’s found on the interior surface at the hinge, the thickest part of shell; thus, it is the fragment you’ll most often encounter on the beach, and one reason the alternative common name, purple-hinged rock scallop, makes sense.

A hinge fragment from a drifted rock scallop Crassadoma gigantea shell rests on the sand. Interior surface exposed.


Speaking of color, occasional drifted valves are darkly stained.

Closeup of an empty drifted Crassadoma gigantea giant rock scallop shell resting interior surface up on the sand.
Closeup of an empty drifted Crassadoma gigantea giant rock scallop shell resting exterior surface up on the sand.


When I first saw the drifted valve below, I didn’t have much in the way of expectations, but when I washed it off and took a closer look, I found that it was an informative find.

An empty and drifted rock scallop Crassadoma gigantea shell, just one valve, partially buried and resting on the sand. Exterior surface exposed.
As I found it
An empty and drifted rock scallop Crassadoma gigantea shell, just one valve, resting on the sand. Exterior surface exposed.
Cleaned off and laid out on the sand
An empty and drifted rock scallop Crassadoma gigantea shell, just one valve, resting on the sand. Interior surface exposed.
Flipped over for a look at the interior surface


A closeup of the same valve shows a nice impression of the smaller, younger scallop before permanent attachment and then some post-attachment growth.

Exterior surface of an empty rock scallop Crassadoma gigantea shell.15 cm rule for scale.
***


Oysters

Oysters occasionally appear on exposed Northern Oregon shores when they arrive on lost floats and buoys. (I think all the oysters shown in this entry are the Pacific oyster Magallana gigas but others are possible.)

A buoy with a few oysters and scars from encrusting organisms now dead and gone. The buoy's resting on the beach. Surf zone and a prominent headland in the distance. Cloudy sky.
Lost buoys arrive on the shore from near and far
Buoy resting on the wet sand just above the surf zone. A couple large oysters and mussels are visible. Cloudy sky.
On what currents has this encrusted drifter bobbed?
Sparse community of large oysters, mussels, and pelagic barnacles on a drifted buoy. There are also scars of past encrusting organisms. The buoy rests on wet beach sand.
Freshly arrived with oyster, mussel, and barnacle hitchhikers


It’s unusual to find empty drifted shells on exposed Northern Oregon beaches. When I’ve come across them, I’ve always assumed that people carried them, they drifted from nearby oyster farming operations, or they arrived on lost buoys as described above, but there could be other explanations.

A bleach-white oyster shell on wet sand.
The exterior surface of a sand-scoured oyster shell
Oyster shell resting on the sand.
I cleaned up the same shell and turned it over to expose its interior
Oyster still life


The set below shows what are probably Magallana gigas from quieter waters.

A dozen oysters exposed on a rock at low tide.
A typical cluster | Mayne Island
A cluster of about ten oysters and their intertidal associates.
Ulva, Fucus, limpets, and acorn barnacles are the Pacific oyster’s intertidal companions | Mayne Island
Closeup on a single oyster on a rock.
The characteristic fluted shell | Mayne Island
Pearly white inside of an empty drifted shell resting on the sand.
The scar on the shell’s interior is where the adductor muscle attaches | Mayne Island
Closeup looking down on a single oyster attached to a rock. Barnacles and Fucus also appear.
The shallowly convex right valve; beneath, the cupped left valve is attached to the rock | Orcas Island
***


Pododesmus macroschisma Green false-jingle

It’s not too uncommon to find small empty shells washed up on the beach. The shell shown in the top panels has experienced quite a bit of erosion.

Green false-jingle, left valve, placed on a bed of acorn barnacles with the outside surface exposed
I moved this shell onto barnacles for a better view | Outside surface
Green false-jingle, left valve, placed on a bed of acorn barnacles with the inside surface exposed
The same shell flipped over to show the inside surface
Thin, nearly circular left valve with radiating lines is a giveaway


For the set below, which is the same shell flipped over, I moved the shell from the swash to drier sand so I could show it off.

Sculptured exterior left valve
Same shell flipped over to expose the namesake green interior of the left valve
***


Clinocardium nuttallii Heart cockle, Nuttall’s cockle

There is a good chance the empty shells and shell fragments so common on some exposed surf-swept beaches arrived via drift.

Single valve on sand looks like half a heart.
Half a heart
Single valve, viewed from the top, on sand, with raindrops dimpling the sand
The shell has pronounced ribs
side view of a single orangish valve on sand
A lovely drifted shell
Upturned shell, internal surface exposed
Chalky internal surface of an eroded shell
Eroded, fragmented valve on sand
Heart cockle shells are relatively thick, but they do erode and fragment over time
***


Corbicula fluminea

Shells of this invasive freshwater (and perhaps sometimes brackish water) clam sometimes wash ashore on the northern Oregon coast.

A clam shell rests on the beach. Other sea wrack and and the surf zone in the background. Partly cloudy sky.
January’s king tide remains
Medium closeup straight down on a clam shell resting on the sand.
Washed downriver and out to sea before landing on the beach
Closeup looking straight down on a clam shell resting on the sand. Morning sunshine on the shell leaves a heart-shaped shadow on the sand.
Asian, golden, prosperity, pygmy, or good luck clam
***


Tresus capax Fat gaper

Bleached fat gaper shells can be abundant on exposed beaches. I’ve examined and measured a bunch of shells on the beaches I’ve visited, but as far as I know, in those locations, I’ve yet to come across the other gaper in our area, Tresus nuttallii.

A mostly intact gaper shell, a single valve, white exterior surface, on sand
Unless you’re seeking gapers in the estuaries, the main way you’ll encounter them is via their empty shells which wash up on exposed beaches
Shell fragment on sand
The shell’s smoothly curved perimeter is interrupted along the posterior edge (lower center) where an opening accommodates the siphons
Shell fragment on sand
A gaper’s interior shell surface, with a pronounced chondrophore (cup-like projection on the left)
Shell fragment on sand
Interior fragment with chondrophore, a point of ligament attachment
Just a small chondrophore among cobbles
After much erosion and polishing, all that remains is the chondrophore | note the growth rings
***


Siliqua patula Pacific razor clam

Northern Oregon has well-known razor clam beds, and empty shells are abundant on most beaches.

A volcano-like mound in the sand, indicating a razor clam beneath
Show indicates a razor clam beneath
Two freshly dug razor clams
Beautiful when freshly dug
Razor clam shell on sand
The shell’s outer coating, the periostracum, starts to wear away as soon as the clam dies
Both valves, exterior surface showing brownish and purple rings
Periostracum gives way to lovely rings
Purple, blue and yellow bands on the shell's interior
A rainbow on the interior | the muscular foot resides in the lower right portion of the exposed valve
***


Tellins

I have always assumed any large elongate tellin I find are Bodega tellins Megangulus bodegensis. By some accounts Bodegas are bay clams, but Kozloff says their habitat is clean sand at the mouth of bays that open onto the exposed coast, and Cowles says exposed sandy shores. Whatever their habitat in life, I show empty drifted shells found on exposed northern Oregon beaches.

Closeup of an empty and drifted Bodega tellin Megangulus bodegensis shell resting on the sand, exterior surface exposed.


Attractive concentric rings on the exterior surface of Bodega shells are a marvel.

Closeup of an empty and drifted Bodega tellin Megangulus bodegensis shell, one valve only, resting on the sand. Exterior surface exposed.
Closeup of an empty and drifted Bodega tellin Megangulus bodegensis shell, one valve only, resting on the sand. Exterior surface exposed.
Closeup of an empty and drifted Bodega tellin Megangulus bodegensis shell resting on the sand, exterior surface exposed.
Closeup of an empty and drifted Bodega tellin Megangulus bodegensis shell, one valve only, resting on the sand. Exterior surface exposed.
Closeup of an empty and drifted Bodega tellin Megangulus bodegensis shell, one valve only, resting on the sand. Exterior surface exposed.
Closeup of an empty and drifted Bodega tellin Megangulus bodegensis shell, one valve only, resting on the sand. Exterior surface exposed.
Closeup of an empty and drifted Bodega tellin Megangulus bodegensis shell, one valve only, resting on the sand. Exterior surface exposed.
Closeup of an empty and drifted Bodega tellin Megangulus bodegensis shell, one valve only, resting on the sand. Exterior surface exposed.
Closeup of an empty and drifted Bodega tellin Megangulus bodegensis shell, one valve only, resting on the sand. Exterior surface exposed.


I rinsed off a couple shells and laid them out for views of both surfaces (If I’ve got my valves down, it’s a right vale in the top two panels and a left valve in the bottom two panels). A yellowish stain is pretty common on the interior of either valve.

A bleached and drifted Bodega tellin Megangulus bodegensis shell (right valve) laid out on the sand for a look at the shell's exterior surface.
Exterior
A bleached and drifted Bodega tellin Megangulus bodegensis shell (right valve) laid out on the sand for a look at the shell's interior surface.
Interior
A bleached and drifted Bodega tellin Megangulus bodegensis shell (left valve) laid out on the sand for a look at the shell's exterior surface.
Exterior
A bleached and drifted Bodega tellin Megangulus bodegensis shell (left valve) laid out on the sand for a look at the shell's interior surface.
Interior
***


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.

Some bleached macoma shells have graceful concentric lines
The macoma hinge isn’t very pronounced
***


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.

Periostracum resembles peeling varnish
The inside of the shell is purple | Orcas Island
***


Saxidomus gigantea Butter clam

In northern Oregon, folks, and I’m one of them, think of butter clams as bay clams. (Maybe they live elsewhere, but I’m not familiar with those places if they exist. Drifted shells aren’t too common on exposed beaches. I’ve seen live butter clams and empty shells in a sand-gravel-shell mix on quiet Salish Sea shores, where I took two of the images below. Butter clams are large, like gapers, but they lack chondrophores, so you won’t confuse the empty shells.

A Bleached shell on wet sand.
Concentric rings are a feature of the shell exterior
Empty clams shells resting on a sand/gravel/shell surface.
Gaper fragment (lower left) for comparison | Mayne Island
Bleached and weathered drifted shell, interior side up, on gravel.
Butter clams are nearly as tall as long | Orcas Island
***


Leukoma staminea Pacific littleneck clam

Widely known as a bay clam in Oregon, littlenecks can also be found intertidally in sheltered settings on the open coast. In such places, empty shells are easy to find, as the two below were.

sandy and rocky substrate, next of some feather boa
Empty bleached shell
Bleached empty shell, both valves
Casting a morning shadow
***


Mya arenaria Soft-shelled clam

Shells you find on exposed northern Oregon beaches have likely drifted there, or humans have carried them.

Drifted from a nearby bay?
Interior surface exposed, left valve, on wet sane
The left valve has a notable chondrophore
Hand-held to show the chondrophore
The soft-shell’s shelf-like chondrophore


Mya arenaria isn’t the only large clam shell with a notable chondrophore—gaper clams also have a beauty, so let’s compare chondrophores. I found the examples below on an exposed beach resting just a few feet apart.

Soft-shell
Shell fragment partially embedded in sand.
Gaper
***


A Sampling of Nestlers

Recognizing the existence of similar alternatives, the nestlers featured below may be something like Hiatella arctica or Petricola carditoides, or maybe both. (If they have orange-red siphon tips, which, incidentally, aren’t too hard to see up close in the wild, that will point to H. arctica.)

The number of living clams and empty shells in some holey substrates is astounding, and in some cases, like the rock in the right-hand panel, it’s easy to pass them by without noticing.

Soft sediment with lots of round holes, some housing clam shells.
Living clams and empty shells in scores of holes in a rock on the edge of a sand-filled pool.
Living clams and empty shells in scores of holes in a sand-scoured rock.


Below are just some closeups of a variety of substrates and settings.


Kozloff describes the succession of nestlers inside the shells of predecessors, and when I looked for myself it was easy to find examples. I count a series of four clam shells in the upper left-hand panel! (And you can see the orange-red siphon tips of the current occupant.)


The siphon tips shown below are pretty stunning. (I guess I include Hiatella arctica and Entodesma navicula among the nestlers with red siphon tips, but Kozloff says those of Hiatella are crimson, and these certainly qualify as crimson.) It’s not too unusual to see exposed red siphon tips like these in small rock crevices during low tides. (Lamb and Hanby mention that siphon openings can be mistaken for those of tunicates. I don’t think I’ve done that here; it’s possible, but I’m pretty sure I could see the shells. Either way, it’s something to be aware of.)

Crimson siphons poke out of a hole in a low intertidal rock.
Crimson siphons poke out of a hole in a low intertidal rock. Smaller siphons appear in adjacent holes.


Another nestler you may encounter is Entodesma. Shown below is a drifted shell I found washed up on the beach. (I didn’t know then that the shells are prone to cracking once they dry.)

Entodesma navicula: exterior surface of the right valve (I think) and a small fragment of the left valve on a white paper background. The shell is dried and cracked. A cm rule for scale.)
Entodesma navicula: interior surface of the right valve (I think) and a small fragment of the left valve on a white paper background. The shell is dried and cracked. A cm rule for scale.)


The clam shown below, which has the Entodesma look, was nestled deep among the mussels in a well-developed bed until it was disturbed and discarded by harvesters. (These are different views of the same clam.)

A view along the ventral edge of an Entodesma clam also shows a posterior gape.
A view of the exterior right valve (I think) of an Entodesma clam.
A view of the exterior left valve (I think) of an Entodesma clam.
***


Penitella penita Flat-tip piddock

Empty shells can be abundant on beaches near sediments suitable for burrowing.

Empty shells on the wet sand.
Flat-tip piddock (bleached) and California mussel
Mostly bleached shell on wet sand.
Remnant periostracum on the shell’s posterior
A bleached piddock shell on sculptured beach sand
Bleached flat-tip and ripples in the sand (the shell’s anterior is at the lower left)


Cobbles and small boulders with piddock workings appear on beaches, where, sometimes at least, they have been dragged, hitching a ride on drifting Nereocystis.

A dark rock with piddock burrows on the most sand.
A few remnant piddock shells remain | Central Oregon
A shale fragment with exposed piddock burrows on the moist sand.
The burrows get wider at the deep end | Central Oregon
Rock with remnant piddock shell fragments resting on the sand.
Shale (I think) with piddock burrows and remnant shell fragments
***


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. 2019. The New Beachcomber’s Guide to the Pacific Northwest. Harbour Publishing.


Online Resources

Netarts Bay Today’s Mollusks page. Accessed June 15, 2023.

It’s worth scrolling down to Bivalvia in Common Sea Life of Southeastern Alaska: A field guide by Aaron Baldwin & Paul Norwood. Accessed June 15, 2023.


Online Species Accounts

Cowles, D. (2002). Mytilus californianus (Conrad, 1837). Invertebrates of the Salish Sea. Rosario Beach Marine Laboratory. Accessed June 15, 2023.

Cowles, D. (2005). Adula californiensis (Philippi, 1847). Invertebrates of the Salish Sea. Rosario Beach Marine Laboratory. Accessed June 15, 2023.

Cowles, D. (2005). Chlamys (Chlamys) hastata (Sowerby, 1843). Invertebrates of the Salish Sea. Rosario Beach Marine Laboratory. Accessed June 16, 2023.

Cowles, D. (2005). Chlamys (Chlamys) rubida (Hinds, 1845). Invertebrates of the Salish Sea. Rosario Beach Marine Laboratory. Accessed June 17, 2023.

Cowles, D. (2005). Clinocardium nuttallii (Conrad, 1837). Invertebrates of the Salish Sea. Rosario Beach Marine Laboratory. Accessed July 21, 2023.

Cowles, D. (2005). Crassodoma gigantea (Gray, 1825). Invertebrates of the Salish Sea. Rosario Beach Marine Laboratory. Accessed July 21, 2023.

Cowles, D. (2005). Entodesma navicula A. Adams and Reeve, 1850. Invertebrates of the Salish Sea. Rosario Beach Marine Laboratory. Accessed October 26, 2024.

Cowles, D. (2005). Magallana gigas (Thunberg, 1793). Invertebrates of the Salish Sea. Rosario Beach Marine Laboratory. Accessed July 21, 2023.

Cowles, D. (2005). Pododesmus macroschisma (Gray, 1850). Invertebrates of the Salish Sea. Rosario Beach Marine Laboratory. Accessed July 24, 2023.

Cowles, D. (2005). Saxidomus gigantea Deshayes, 1839. Invertebrates of the Salish Sea. Rosario Beach Marine Laboratory. Accessed July 23, 2023.

Cowles, D. (2005). Siliqua patula (Dixon, 1788). Invertebrates of the Salish Sea. Rosario Beach Marine Laboratory. Accessed July 24, 2023.

Cowles, D. (2005). Tresus capax (Gould, 1850). Invertebrates of the Salish Sea. Rosario Beach Marine Laboratory. Accessed July 24, 2023.

Cowles, D. (2006). Nuttalia obscurata (Reeve, 1857). Invertebrates of the Salish Sea. Rosario Beach Marine Laboratory. Accessed July 23, 2023.

Cowles, D. (2006). Penitella penita (Conrad, 1837). Invertebrates of the Salish Sea. Rosario Beach Marine Laboratory. Accessed July 23, 2023.

Cowles, D. (2006). Petricola carditoides (Conrad, 1837). Invertebrates of the Salish Sea. Rosario Beach Marine Laboratory. Accessed June 15, 2023.

Cowles, D. (2007). Leukoma staminea (Conrad, 1857). Invertebrates of the Salish Sea. Rosario Beach Marine Laboratory. Accessed July 24, 2023.

Cowles, D. (2007). Mya (Arenomya) arenaria Linnaeus, 1758. Invertebrates of the Salish Sea. Rosario Beach Marine Laboratory. Accessed July 24, 2023.

Cowles, D. (2014). Tellina bodegensis Hinds, 1845. Invertebrates of the Salish Sea. Rosario Beach Marine Laboratory. Accessed June 15, 2023.

Hiebert, T.C. 2015. Entodesma navicula. In: Oregon Estuarine Invertebrates: Rudys’ Illustrated Guide to Common Species, 3rd ed. T.C. Hiebert, B.A. Butler and A.L. Shanks (eds.). University of Oregon Libraries and Oregon Institute of Marine Biology, Charleston, OR.

Hiebert, T.C. 2015. Hiatella arctica. In: Oregon Estuarine Invertebrates: Rudys’ Illustrated Guide to Common Species, 3rd ed. T.C. Hiebert, B.A. Butler and A.L. Shanks (eds.). University of Oregon Libraries and Oregon Institute of Marine Biology, Charleston, OR. Accessed July 24, 2023.

Hiebert, T.C. 2015. P. penita. In: Oregon Estuarine Invertebrates: Rudys’ Illustrated Guide to Common Species, 3rd ed. T.C. Hiebert, B.A. Butler and A.L. Shanks (eds.). University of Oregon Libraries and Oregon Institute of Marine Biology, Charleston, OR. Accessed July 24, 2023.


I updated this page on December 15, 2024