Many of the species of scallops grow large enough to have commercial interest. The most important species in Japan is P. yessoensis, otherwise known as the giant ezo scallop. This is a cold water species living in the northern areas of Honshu Island and Hokkaido, where the main culture areas are to be found. Other important species cultured in Japan are the fan shell scallop P. albicans, and the queen scallop C. nobilis. Each has its specific Japanese name. In the USA the principal species of interest are the Bay scallop, A. irradians, the calico scallop, A. gibbus, and the purple hinge rock scallop, H. multirugosus. In Canada, the giant scallop, P. magellanicus, is the most important in terms of harvested quantities. The Pacific calipo scallop, C. circularis, found along the Mexican coast, the Chilean A. purpuratus, and the Argentinean C. patagonica are all commercially important species. Two valuable species are found in European waters, the King scallop, P. maximus, and the smaller species C. opercularis, also known as Queen scallop. Other important species in Europe are the Icelandic scallop, C. islandica, and the Greek scallop, C. glabra. Other commercially important scallops are: P. fumata or Australian scallop, A. pleuronectes or Asian moon scallop, C. farreri, A. japonicum, and P. novaezealandiae.
The commercial sizes of scallops vary with species. The Japanese scallop are commerical size when they are 10–11 cm in length and 2–3 years old. Most species are protected by legal minimum sizes (based on maximum shell length) for harvest; in Hokkaido, Japan, the regulation of shell lengths is 82 mm or more, while in Mutsu Bay the shell length must equal 100 mm or more.
Fig. 1. World production of scallop
Other features which differentiate the species are color of shell (white, red, pink, orange or brown, etc.), shape, and sculpture patterns. However, the most important key taxonomic features are concerned with shape and dimensions of the ears, shape of the valves, and kind of radiating ribs.
Scallop also differ with regard to the environmental niches they occupy. The niches are not determined by food preferences as with many other filter feeders, but by bottom composition and depth. For example, the European King Scallop, P. maximus, are found from low water to 60 fathoms, and prefer bottoms of clean, firm sand, fine gravel, or sandy gravel, but are rarely found on muddy sands. On the other hand, the European Tiger Scallop, C. tigerina, lives down to 50 fathoms and prefers bottoms of coarse, sandy mud, gravel or stones (Tebble, 1976).