Clams belong to the group of animals called bivalves, which includes clams, mussels, oysters, and scallops. The soft body parts of these animals are enclosed between two shells; hence, the word bivalve. Bivalves are closely related to limpets, abalone, snails, slugs, squids, and octopuses. These animals, including bivalves, are collectively called mollusks.
Most bivalves reproduce by discharging sperm and eggs into the water where fertilization occurs. Some will spawn only when the water temperature reaches a critical level. The fertilized eggs develop into microscopic larvae, which are carried about by water currents for various lengths of time (usually 3-4 weeks) before setting, depending on the particular species and water temperatures. The larvae feed on microscopic organisms called plankton, and most species, after developing to the advanced stage, settle on and attach to gravel, shell, or sand grains, then burrow into the bottom. In contrast, oyster larvae cement themselves to hard, clean surfaces such as rocks and shells.
Since larval clams spend a considerable amount of time drifting about in the water before settling, the location where a particular larva ends up may be many miles from its parents. Many people assume that, if they transplant adult clams to their beach, they will soon populate the beach with clams. If the transplants survive and spawn, the resulting offspring will likely be scattered for several miles. A successful set of young clams on, any particular beach depends on a mass spawning of adult clams in a very large area, and on setting and survival on the beach in large numbers.
Hardshell clams include Manila and Native littlenecks, Butter clams, Cockles, Macomas and a few others of little harvest interest. These clams are found on beaches of mixed sand, gravel, and mud. They are commonly harvested using shovels or rakes. Except for the larger butter clams, rakes are usually most effective, and are less damaging to the clams and the beach
Manila and Native clams are similar in appearance and grow to 3 or 4 inches in length. The shells of both species have concentric rings and radiating ridges, making a kind of lattice sculpture. Manilas seem to have more distinct radial sculpture at the posterior end. Both species can draw their siphons completely into their shell.