A clam, according to Merriam-Webster, is "any of numerous edible marine bivalve mollusks living in sand or mud." But what classifies a seafood eatery as a "clam-shack"? Not so easy to define, although Nutmeggers understand the concept.

Clam shacks are clearly Connecticut icons, and although high on the casual end of the dining spectrum, these eateries attract everyone, from celebrities (see who we’re talking about below) to local teenagers and families.

While the number of clam shacks in Connecticut is unknown, since there is no regulatory designation, customers have been eating them up for decades. Most are open only seasonally, making them extra special. Picnic tables, paper plates, and a particular atmosphere are among the key ingredients for a clam shack.

In a nutshell, a clam shack is a state of mind.

We’ve picked the best-known shacks along the shoreline and asked their chefs, managers, and owners what it is about their digs that makes customers happy as clams who always come back for more.

Chick’s opened on the beach in 1950, and the drive-in is still owned by Joseph "Chick" Celentano, whose son, Mike, now manages the place.

"It’s a high-volume business in the summer because we’re right on the beach. It’s a bit of insanity," Mike admits.

The most famous items at Chick’s are hot dogs, fried clams, and lobster rolls.

"On a good weekend day we can have 3,000 to 3,500 customers," Mike notes.

That means tens of thousands of hot dogs are served. "Whole-belly clams are popular, although they’ve gotten very expensive," Mike adds. He orders several gallons of clams every day and can do "100 orders of clams a day in the summer when things are really cranking." This equates to a few thousand orders of claims over the summer.

It’s so busy that celebrities probably pop in but Mike, frankly, hasn’t recognize any. Chick, however, purchased Jackie Gleason’s house in the early ‘90s and still owns it.

Lenny’s Indian Head Inn, a seven-day a week year-round clam shack, has been a favorite for yachters, visitors, and locals since 1968. Lenny’s sports a "spiffy" new dining room, a pub room, and a "back porch" overlooking the Sybil Creek tidal marsh and osprey area.

"We’re known for our lobsters, steamers, and whole clams—the whole fried dinner," says chef Christopher Conlin. "We serve hundreds and hundreds of meals every weekend during the summer. It’s a super-large number," he added.

"Young, old, rich, and poor—they all mingle well together here," says Bill’s Seaford manager Mark Leopoldino.

Specifically, they mingle over lobster rolls and fried seafood platters, which are the two most popular menu items.

"We make thousands of seafood platters every summer, and tens of thousands of lobster rolls," he said. On a summer day, Bill’s can serve 250 lobster rolls. Third and fourth place in popularity are steamers and prime rib, respectively, according to manager Kathleen Johnson.

Harrison Ford visited last summer with his girlfriend, Calista Flockhart, and local athletes Vin Baker and Ray Allen are regulars.

"A lot about Bills makes us stand out—the customers, the music, the outside dining," Leopoldino stated.

In the clam shack business for 51 years, Johnny Ad’s serves a diverse crowd with celeb customers such as Dominick Dunne, columnist Liz Smith, the late Art Carney, and Herb Chambers (who visits in his Rolls Royce). Whole clams, followed by lobster rolls, are the most popular seafood items on the menu. For 300 to 400 landlubbers per day in the summertime, hot dogs are the must-order, according to co-owner Tenzin Lama.

The combination of the quality of the food, how it’s cooked, and the tartar sauce is what sets Johnny Ad’s apart, according to co-owner Bob Hansen.

"We have always used the most expensive frying oil—cholesterol free—and separate the Fryolators so that clams, fish, cod, shrimp, fries, and onion rings are always apart. The oil is filtered or changed throughout the day, which stops the whole production line.

"Most places don’t go to that extreme," Hansen adds. The tartar sauce has "almost always been homemade," Hansen reports and added that the recipe has been around now for 50 years.

The past 10 years have brought more traffic to Johnny Ad’s as well as many other shoreline restaurants, observes Hansen. Nonetheless, the waiting time is less than it used to be.

"People used to wait over an hour for clams, but it’s actually less now because there are many more choices," he said.

Dad’s Restaurant, originally known as the Harbor Drive-In, was named after the original owner, Dave Waddington, who owned the restaurant for 35 years. Current owner Peter Salomonson explained that "Dad" had four daughters who would always say to their mother, "Let’s go down to Dad’s for dinner." So, he changed the name. Salomonson , who has owned Dad’s with his wife, Debra, for a decade now, purchased the restaurant from his best friend who wanted to retire.

"It’s been here so long that people have been coming here for generations. I’ve got grandparents coming in with their grandchildren, telling them that they were dining here 45 years ago," Salomonson said.

Whole bellies are the most popular, followed by clam strips and lobster rolls. In a week, Dad’s can go through 25 gallons of whole bellies and 18 to 20 gallons of clam strips.

"It’s not unusual for us to serve 1,200 to 1,400 plates of food in one day. It’s a high-volume seasonal restaurant open late April through late September," Salomonson said.

Scot Haney dines here with his crew when he’s in the area. Other than Haney, "I don’t think anyone famous comes to Niantic. It’s really not a destination town," states Salomonson.

Fred’s Shanty, named after former owner Fred Pulous, is found on New London’s waterfront. First opened in 1972 and now owned by John Hesserman, Fred’s is famous for "seafood—fresh whole-belly clams, fresh clam strips, fresh scallops, fish and chips, calamari—you name it," says Hesserman, who is in his ninth season. "Of course, we serve our famous foot-long hot dogs. We’re most famous for them."

Fred’s stays open for an extended season The owner didn’t know how many foot longs are served each summer, but says the number is somewhere in the thousands.

Abbott’s, founded in the 1940s, didn’t start serving lobsters outdoors until 1963. Jerry Mears and his wife bought the successful restaurant in 1981, grew the business considerably, and added Costello’s Clam Shack 12 years ago.

Abbott’s claim to fame is, of course, the lobsters.

"The hot lobster roll has won awards all over the place," said Mears while wintering in Florida. "It’s lobster meat on a roll, with hot butter. That’s it—very complicated. The average chef couldn’t make it," he joked.

Maybe not complex, but Abbott’s hot lobster rolls are known around the world.

"We sell upwards of 40,000." Not bad, since the restaurant is open only 125 days a year.

"People come to us because they can’t get the quality lobster we use." And, they taste great because of a unique (secret) cooking process that, to Mears’ knowledge, nobody else uses.

"The lobsters never go into water. It’s all cooked live in hot steam," he noted

Of course, he won’t share exactly how they do it.

Costello’s, only about a quarter of the size of Abbott’s, is best known for fried clams, although the fish and chips is a close second. While Mears has never counted, "it’s way into the tens of thousands. The number will make your head spin if you think of the number of clams we use."

Celebrity customers have included Meryl Streep, Jimmy Carter, Jacques Pepin, Morley Safer, Philip Scheffler Charles Kuralt, Buddy Hackett, and many more. Mears has been told that David Letterman has been in, which make sense since Letterman has plugged Abbott’s on his show.

Famous for seafood (particularly clams), chowder, and ice cream, Sea Swirl offers casual outdoor dining in a clam shack atmosphere on the flood tide of the Mystic River. Formerly a street-side Carvel Ice Cream shop, the restaurant has been owned and operated by the Blaney family for 23 of the 52 years the building has been there.

The hallmark entree is fried whole-belly clams, which have a wonderful reputation, winning an Editor’s Choice award as well as "best of the best" clam shacks accolades. Sea Swirl serves "hundreds each week," says David Blaney. Fried seafood, including scallops, shrimp, and clam strips are also offered, along with off-site catering known as Catering ByThe Sea.

Barbra Streisand once dined here, and Rachael Ray of the Food Network Channel featured the fried fish sandwich on her "$40 a Day" show.

Cove Fish Market is the only clam shack in the Mystic area open year round, "since we are the only ones with cozy indoor seating," say father and son owners Andrew and Zachary Kowal. As the name implies, the Kowals also operate a fresh fish market, which provides local, native fresh fish and lobsters for the clam shack.

Cove Fish Market was recently recognized by Esquire magazine, as their fried cod sandwich made the "coast-to-coast list of the finest meals on sliced bread" (March 2008). Cove is also famous for fish and chips and clear broth Rhode Island-style chowder, as well as cited for the best lobster outside of Maine.

The hallmark entrée, fish & chips, is a "local native flounder, lightly battered and deep fried, served with premium long cut French fries and our own coleslaw." Approximately 9,000 fish and chips entrees are served (150 on a busy day), with 7,011 of these served from June through September.

Celebrity clients include Conan O’Brien, Scott Burrell, and members of the Connecticut Sun Basketball team.