STORY TOOLS

• E-mail story
• iPod friendly
• Printer friendly

Tell us about it

• What would you add to this story? Tell us what we missed.
• Do you have photos from this event? Documents we need to see? Share with us.
• Upload photos & videos
• More ways to get your stuff online and in the paper.

More Latest Stories

• Kretch’s, a long-standing Marco eatery
• Ray Nesbit, a seamless musical performer
• You Review Food: Amy Perez

Share and Enjoy [?]

Wow — those fireworks on the Fourth of July were spectacular!

I arrived at Residents’ Beach around 6 p.m. on the holiday, and after linking up with friends, went for a beach-combing jaunt at the water’s edge.

I passed some sand sculptures. One was an extra large rendering of a sea star and the artist had covered the top with at least a hundred calico scallop shells.

As I wandered along the tidal pools, I saw many more of these colorful shells. So I was inspired to write about the natural history of this common, but very unusual animal.

This year-round resident of Marco’s waters, the calico scallop (Argopecten gibbus), can grow as large as 2.5 inches and is a bivalve with two fan-shaped shells (valves) that are mirror images of one another except for color. Near the hinge, where the two valves meet, the shell is flared out on each side, forming small “wings.”

The upper valve has brightly colored patterns of rose, pink, purple, or orange. The lower valve is usually white, with more color closer to the hinge, although sometimes the color extends to the edge of the valve. Both valves have 17 to 23 squared ribs which radiate from the base.

Scallops cannot dig into the sandy bottom as clams do, so the darker patterned top valve helps camouflage scallops as they sit on the sea bed. The top valve often has barnacles, slipper shells, or sponges growing on it, adding to the camouflage.

Most bivalves have two adductor muscles to the right and the left of the hinge; these muscles hold the two valves closed. The scallop, however, has one large central adductor muscle. (When you dine on “sea scallops” at a restaurant, you are eating the adductor muscle of another species of scallop that can grow as large as eight inches.) The adductor muscle provides the power which allows this animal (along with all members of the true scallop family) to do something no other bivalve species can do — swim!

To swim, the scallop opens its valves to pull in water, and then quickly claps the valves shut with the adductor muscle. As the valves close, the mantle, which is a thin sheet-like organ that creates new shell material, directs the flow of water. If it forces all of the water to shoot out through the back hinges, the scallop moves forward through the water via jet propulsion. If the water is forced out around the margins of the valves, then the scallop can swim backward.

The mantle is not just a smooth sheet of tissue; there are many fleshy tentacles extending from the mantle’s edge. These tentacles have sensory roles and are sensitive to chemicals in the water, especially those produced by predators of scallops. So scallops are able to “smell” a predator, such as a sea star, and respond by clamping their valves shut for protection, or swimming away. A scallop can swim for a few seconds up to two minutes, depending on currents and the severity of the threat.

When the scallop’s shell is gaped open, you can see the sensory tentacles as well as the scallop’s most interesting feature — two rows of tiny, bright blue eyes, about 20 around the margin of each valve. These eyes have a cornea, lens, and retina, structures also found in human eyes. Because of their eyes, scallops can sense motion and shadows, so a crab or fish trying to sneak up and grab a snack will be seen, and the valves will close. Should the scallop lose an eye, it is able to regenerate another.

While scallops can’t be said to have a brain, they do have a nervous system that is unusually concentrated, with a complex, fused central ganglion which is the largest and most intricate of all the bivalve species in the world. The way scallops react — swimming away from danger, orienting their shells, and responding to movement and shadows — indicate that they can process the information from what they see and “smell.” The blue-eyed calico scallop — the world’s smartest bivalve!