【Reading】かいばしら

【English Name】Kaibashira (Adductor Muscle)

Kaibashira is the colloquial name for the adductor muscle (heikakukin) in bivalves, referring to the muscle tissue that bears the role of closing the shells together. It is counted among the toppings familiar in the world of sushi as well.

Structurally, the ligament located at the apex of the shell always acts, through its elasticity, in the direction of opening the shells. The adductor muscle counteracts this force, directly connecting to the inner wall to bring the left and right shells into close contact and maintain the closed state. When the function of the adductor muscle is impaired by heating or cutting, only the elasticity of the ligament remains and the shells come open—such is the mechanism.

In short-neck clams (asari) and freshwater clams (shijimi), two adductor muscles provided front and rear exist at nearly equal size. In the scallop (hotategai), on the other hand, only the single rear one develops to an extreme degree, occupying the center of the shell—corresponding to the monomyarian (single-muscle) type. The pen shell (tairagi) and blue mussel (murasaki-igai) and the like exhibit the heteromyarian (unequal-muscle) type, in which the rear is markedly larger than the front.

Representative edible kinds are the scallop, pen shell, Japanese scallop (itayagai), and itaragai. Such species possessing developed adductor muscles are recognized as having high value as fishery resources. At sushi restaurants, the adductor muscles of the scallop and pen shell are served in the form of nigiri or gunkan. In Chinese cuisine, the dried product is called "yaozhu," completed through the processes of boiling and roast-drying.