Explore your sweet (or bitter) side this Valentine’s Day with the western bittersweet

Eyes Under Puget Sound – Critter of the Month

A round clam shell with tan-and-white markings sits on a background of fine brownish-gray sand.

Western bittersweet shell on the beach. © J. Duane Sept (Image from The New Beachcomber’s Guide to the Pacific Northwest)

Ah, Valentine’s Day — no other holiday has the power to conjure up feelings of eager anticipation in some, and anxious dread in others. Love can bring both joy and pain into the lives of those who experience it, so what better critter to represent the most complicated of emotions than the western bittersweet?

What’s in a name?

Kingdom Animalia, Phylum Mollusca, Class Bivalvia, Order, Arcida, Family Glycymerididae; Genus Glycymeris, Species: G. septentrionalis
Sometimes referred to as the button shell, the Pacific coast bittersweet, the northern bittersweet, and the California bittersweet, this little clam goes by many names. The genus name Glycymeris comes from the ancient Greek words for sweet (glykys) and part (meris), describing the sweet and nutty flavor of this bivalve group. Although the western bittersweet is not a commercial favorite in its native range of Alaska to California, you may find its relative, Glycymeris glycymeris, on the menu in Europe, where it is known as the dog cockle or sea almond. Sounds like a food you could either love or hate!

Bare your teeth

3.	A pried-open clam shell with two blue arrows drawn to point at small white shell “teeth” that are along where the shells connect at the h

The shell of this western bittersweet is open, revealing the bright orange foot of the animal inside. Hinge teeth are indicated by blue arrows. Photo by Dave Cowles, wallawalla.edu

The western bittersweet belongs to the family Glycymerididae, one of the few families in Puget Sound which have taxodont dentition. This means that it has interlocking teeth on the inside of its shell around the hinge where the two valves meet. This feature is useful in telling it apart from the similar-looking Pacific littleneck clam, Leukoma staminea, which is similar in shape and also has radial ribs running down its shell.

The habitat of the bittersweet is also a giveaway — the littleneck lives intertidally, while the bittersweet finds subtidal conditions more to its liking. It buries itself on sandy or gravelly bottoms, happy to stay in one place until its light-sensitive eyespots detect potential danger. Then it uses its muscular foot to push itself to a safe location. Bittersweets are uncommon in Puget Sound, but we have collected a few of them from Pt. Townsend, Mutiny Bay, Dyes Inlet, and Oakland Bay, in depths up to 95 meters.

Top: Two different pattern shells with bright tan-and-white markings. Bottom: Five shells mostly white color with faded tan markings.

Top: Two shells showing the variable coloration. Photo: Kelly Fretwell. Bottom: Several worn shells; the dark periostracum is visible in all but the bottom-right. Photo: Dave Cowles, wallawalla.edu

Beauty fades

Although true beauty comes from within, some western bittersweets are striking on the outside too, with variable brown-and-white zig-zag patterns on their thick, rounded shells. Others are a more drab solid brown or white. All start out with a dark brown layer of protein called the periostracum protecting the growing edge of the shell, kind of like a furry beard.

Eventually the slow hand of time fades the bright colors, wears off the periostracum, and files down the ribs of the shells until they are almost smooth in appearance — wrinkles in reverse! Far from detracting from their beauty, these marks of long lives well-lived in Puget Sound are a sweet thing indeed.

Critter of the Month

Our benthic taxonomists, Dany and Angela, are scientists who identify and count the benthic (sediment-dwelling) organisms in our samples as part of our Marine Sediment Monitoring Program. We track the numbers and types of species we see in order to understand the health of Puget Sound and detect changes over time.

Two female scientists wearing hard hats and life jackets smile from the back deck of a research boat on a sunny day.

Dany and Angela share their discoveries by bringing us a Benthic Critter of the Month. These posts will give you a peek into the life of Puget Sound’s least-known inhabitants. We’ll share details on identification, habitat, life history, and the role each critter plays in the sediment community. Can't get enough benthos? See photos from our Eyes Under Puget Sound collection on Flickr.