Although we all recognize the ubiquitous fan shape of the scallop shell, many of us are confused when it comes to distinguishing what’s inside the shell.

Scallops are bivalves (mollusks with two hinged shells), but they’re unique in that the muscle that opens and closes the two shells (the adductor) is, in fact, the sweet, tender nugget of meat we like to eat.

Although there are hundreds of species of scallops in the world’s oceans and bays, only a handful are commonly available. The largest and most popular aresea scallops,从东部大西洋的主要收获Canada to North Carolina, but also from Peru, Japan, and Russia. Available year-round, sea scallops are sorted and marketed by size, with the most popular about 1 to 112 inches in diameter and 34 to 1 inch high. It usually takes 20 to 30 of these sea scallops to total 1 pound (you’ll see them marked 20/30 count). They range as large as U-5s (5 per pound) and as small as 40/50 count. Typically, the larger the scallop, the higher the price.

Bay scallopsare smaller than sea scallops (about 12-inch in diameter, 50 to 100 per pound) and are considered to be the sweetest and most succulent. Cape bays harvested from Long Island to Cape Cod are especially prized. Sold fresh, these bay scallops are a seasonal specialty (available in the fall and early winter), and are generally quite expensive. Less desirable are frozen Chinese bay scallops which have been imported in increasingly large numbers in recent years.

A third variety is now available in the markets.Calico scallops, harvested from the warm Atlantic and Gulf coasts of Florida as well as Central and South America, are even smaller than bay scallops (100 to 200 per pound), but they’re the least expensive—and the least esteemed. Most commercial calico scallops have been briefly steamed in order to quickly shuck them, so their flavor and texture are compromised. Calicos are often mislabeled as bay scallops. While their cheap price should be a dead giveaway, calicos are generally smaller and darker than true bays. In my fish market in Vermont, I usually see calicos for about $5 per pound; bay scallops, when in season, can be anywhere from $14 to over $20 per pound—but they’re worth it. Sea scallops aren’t cheap either—between $9 and $12 per pound in my market.

Ask the fishmonger for “dry” scallops. Freshly harvested scallops are 75% to 79% water, but in the hours, days, and sometimes weeks before scallops reach your kitchen, they begin to dry out and lose moisture. To offset this, commercial fisheries have developed a method of soaking fresh scallops in a solution of salts and water (sodium tripolyphosphate, or stp) to plump the scallops and keep them fresher longer. Unfortunately, not only are you paying for this extra water, but you’re getting an inferior product. The soaking detracts from a scallop’s natural fresh, briny taste, and when you try to sauté a soaked or “wet” scallop, it instantly sheds all its excess water when it hits the hot pan. You wind up steaming your scallops rather than searing them, and the texture of the meat tends to be rubbery.

In a truth-in-labeling initiative, the FDA issued a policy in 1992 urging retailers to label scallops that have been treated with stp. It’s worthwhile to seek out a fishmonger who sells “dry” scallops (many do), but if you wind up having to cook “wet” scallops, be sure to dry them thoroughly with paper towels before cooking.

As with any seafood, shop for scallops with your eyes and nose.Fresh scallops should appear moist but not milky. Refuse any that have a feathery white surface (a sign of freezer burn) or dried and darkened edges (a sign of age). Always ask to smell scallops before buying. They should smell somewhat briny and seaweedy, but not offensive, sharp, or at all like iodine. If the scallops have no smell and a uniform stark-white color, chances are they’ve been soaked in stp.

Cook scallops the day you buy them, if possible.If not, store them in the coldest part of your refrigerator. I sometimes nest the bag or container in a larger bowl of ice to ensure that they really stay cold. But avoid direct contact with ice—it will leach flavor and deteriorate the texture of the scallops. Also, try not to rinse scallops, as this will wash away flavor.