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Marine Fossils and their Living Relatives

Fossil: Giant Pecten 
Pecten propratulus 

Scallops (or pectens) have flat shells and distinct flat extensions to the hinge line called "wings" In western Washington, giant fossil scallops are generally more than 85 mm wide and are found in rocks that are 35 million to 5 million years old.

The very large family Pectinidae contains thousands of fossil species and hundreds of living species. Scallops first appeared in the Triassic (about 230 million years ago) and have always been more numerous in warm shallow seas. Pecten propatulus can be 100 mm wide and is found in rocks around Clallam Bay that are approximately 20 million years old.

This species has shells ornamented with 27 or 28 flat ribs, and the wings on the hinge line have a distinct notch. The ribbing on the right valve (or shell) looks different from that on the left valve and these have often been mistaken for two different species. 

Much smaller scallops are found in older rocks in western Washington. The oldest is Pecten landesi from 40-million-year-old rocks in Cowlitz County; it measures only about 30 mm in width.

pecten propatulus
Fossil Pecten propatulus, right valve, with flat-topped ribs.
Photo by Ron Eng

pink scallops
Pink scallops, Chlamys hastata, feeding.
Photo courtesy of PTMSC

Pink Scallop 
Chlamys hastata

The pink scallop is sometimes called the "swimming scallop" because of its remarkable ability to swim. It does this by clapping together its two lightweight shells (or "valves"), forcing the water out around the hinge, creating a kind of jet propulsion. Many other scallop species are also capable of swimming.

Most of the time the pink scallop rests on the bottom with its two valves agape, drawing water inside to filter out microscopic food with its gills. Around the margin of the animal are two rows of beautiful iridescent eyes. Although it cannot see clear images, it is very sensitive to changes in light intensity around it. When a scallop is startled or approached by a predator, it takes off, looking very much like a set of animated false teeth "biting" the water around it.

Pink scallops live along the coast anywhere from a few feet below low tide to deep water. Young scallops can sometimes be found on the undersides of docks and floats, attached by a byssus (threads similar to the attachment used by mussels).