Hard-shell littleneck clams:
Native littleneck: Small clams with rounded, gray-brown shells and ivory meat with brownish siphons. They're best suited for steaming or sautéing.
Native butter clam: The shells are somewhat smooth with fine lines running across the surface. Butter clams have tender meat with a pink-ivory color. Serve on the half-shell, steamed, sautéed or fried.
Manila: This clam was imported at the end of the 19th century from Japan along with the Pacific oyster, and it has thrived well in Northwest waters. The shells are light-gray with darker stripes. The meat is ivory in color with a darker siphon and is very tender. Manilas are best steamed with various seasonings, sautéed or fried or served raw on the half shell. Manila clams hold longer after harvest, which is why this is the clam of choice among retailers.
Geoducks: Looking like creatures that have escaped a sci-fi flick, these giant Pacific Northwest clams have protruding siphons and average about 8 to 12 inches long. Geoducks are the exception to the closed-shell rule: They gape open because the clam is simply too big for its shell. But if the siphon retracts when touched, the geoduck is alive.
To prepare geoducks after soaking, immerse in boiling water a few seconds, then drain and rinse with cold water. Pull off the skin of the siphon.
Use a small paring knife to cut through the muscle attachment on both sides of the shell and remove. Cut the siphon off at its base and slice away the tip; discard the dark digestive gland. Chop or grind for chowder or cut open lengthwise and slice into steaks or strips for sautéing.
Much like abalone, geoduck steaks should be pounded or scored to tenderize them. Cook them very briefly, a few seconds per side, as they will toughen quickly.
Horse clams: These also grow to a large size, up to 8 inches in length. They resemble the geoduck, and their siphons must also be skinned and the digestive glands cut away. Many claim these are the best clams for chowder but that their toughness is suited for little else. Grind the meat for chowder in a food processor, or chop finely and add toward the end of the cooking time.
Razor: The clams have long, narrow shells up to 10 inches long with slightly rounded, sharp edges. They are fast diggers, so they're a challenge to harvest.
After cleaning and soaking, prepare razors for cooking by cutting through the muscle attached to the top and bottom shells to remove the clam meat.
Cut away dark patches such as the tip of the neck and the gut muscle. Razor meat is sweet and juicy and is best when cut in half and dredged in flour, batter or crumbs for frying, or chopped for fritters and chowders.
Sources: "The Encyclopedia of Fish Cookery" by A.J. McClane; "Northwest Bounty" by Schuyler Ingle and Sharon Kramis; "Pacific Northwest Palate: Four Seasons of Great Cooking" by Susan Bradley; "The Great American Seafood Cookbook" by Susan Herrmann Loomis.