General Information

Indigo underwater eyes: Sea scallops

The eyes of a scallop. Photo courtesy of Wikimedia Commons

By Pat Garber

When you walk along the Ocracoke beach, you will come across the red-and-white shells of a creature known as the calico scallop.

Although the closely related bay and sea scallops are great eating here on the island, the most amazing thing about scallops is their blue eyes–hundreds of them–arrayed across the opening of their shells and glittering like an azure underwater necklace.

Each eye–about the size of a poppy seed–sits at the end of a tentacle which can be extended beyond the rim of the shell. Each eye, scientists say, has a lens, a pair of retinas and a mirror-like structure.

Until recently, little was understood about how these eyes actually work.

A study published in the journal “Science” in November 2017, detailed how a team of Israeli researchers using powerful cryo-electron microscopes discovered amazing new information about the eyes of scallops.

Bay scallops, top, and calico scallops on the Ocracoke beach. Photo: C. Leinbach

According to Dr. Benjamin A. Palmer, who was part of the study, each eye contains a miniature mirror composed of millions of square tiles. The mirrors reflect light onto two retinas in much the way that reflector telescopes look into space.

The study also postulated that one of these two retinas creates a sharp image of what is right in front of the scallop, which may help it quickly identify predators. The other retina provides a view of the periphery, which may aid in locating good feeding areas.

The many eyes all send messages to a single cluster of neurons, which combines the information to form a vivid picture of the scallop’s environment.

Scientists are puzzled as to why these rather simple bivalves would have evolved such elaborate eyes.

Palmer says that scallops have evolved a mastery of crystal formation that scientists hadn’t thought possible. Understanding how they do it might prove useful in new inventions, such as cameras which can take pictures in dim seawater.

Scallops are mollusks, in many ways resembling other bivalves such as clams or mussels.

Unlike most bivalves, which as adults are limited in mobility, scallops can move quickly, bouncing along the bottom as they open and close their valves, using the adductor muscle to expel water forcefully between the mantle flaps.

Seven species of Pectinidae (their Latin name) inhabit southeastern waters.  Most have radial ribs, concentric ridges and flattened, triangular extensions known as “ears.” One valve is more inflated than the other.

Atlantic calico scallop, possibly lunch for a boring whelk. Photo: P. Vankevich

Bay scallops used to be numerous in Pamlico Sound.

Ocracoke native Della Gaskill, born in 1937, recalls that when she was a child bay scallops provided part of her family’s income. During the winter her father, grandfather and uncle would go scalloping, and she would help by opening the scallops, which were then put in gallon jars and sold.

The mollusks have declined in the waters around Ocracoke since the early 20th century, probably the result of a die-off of eelgrass, to which they cling to prevent being buried.

Young bay scallops also are subject to predation by skates, which have increased in number in recent years.

Scallop shells on the beach are still plentiful.

Notice the beautiful scallop shells next time you walk an Ocracoke beach, and when you pick one up, imagine it scooting along the marine floor and watching everything with its amazing blue eyes.