Scallops Bivalves - Scallops more than any other group of bivalves have attracted the interest of naturalists and collectors for centuries. ‘In appearance no other molluscan shells have so pleasing a design and range of colours as pecten shells . . .’ (Cox, 1957). In the king scallop, Pecten maximus, the left valve is flat and is slightly overlapped by the right one, which is convex (Fig. 2.4A). Adults recess in the substrate with the flat valve uppermost. The two valves, which are roughly circular, are held together along the hinge line by a rubbery internal ligament. Typically, there are 15–16 ribs radiating from the hinge. These alternate with grooves and give the scallop its distinct comb-like appearance. There are two projecting ‘ears’ or auricles on either side of the umbo; these vary in size and shape and are used, along with other shell characters, to differentiate one species of scallop from the next (see Table 2.1 for shell characters used in species identification). There is a large, centrally placed, adductor muscle, a standard seafood commodity that is widely traded and universally available (Dore, 1991).
Distinct annual rings on the shell, make ageing of scallops a relatively easy task, compared to mussels and oysters. Shell size in scallops varies quite a bit depending on the species: P. maximus can be up to 150mm in length, while the sea scallop, Placopecten magellanicus, and the yesso scallop, Patinopecten yessoensis, can reach a size of 200–230mm. Other species such as the queen scallop, Aequipecten (Chlamys) opercularis, the Icelandic scallop, Chlamys islandica and the bay scallop, Argopecten irradians, seldom grow larger than 100mm.
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| Scallops bivalve |
The beautiful colours that are a feature of scallop shells are laid down when the shell is being formed. In P. maximus the colours range from off-white to yellow to light brown, often overlaid with bands or spots of darker pigment. In A. irradians, background colour of the shell and overlying pigment distribution appear to be coded by at least two separate genes (Adamkewicz & Castagna, 1988).
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