Akagai

The flesh runs red because its blood is said to carry hemoglobin, much like ours. It has a crisp, clean bite, and chewing releases a faint iron-tinged flavor. In Edo-style sushi it comes with himo, the frilled mantle edge sliced alongside, chewier still and carrying an even stronger briny note. Eaten raw, the contrast between its redness and its sweetness stands out clearly; cooking tends to toughen and shrink it, so it is treated as a shellfish best eaten raw.

This bivalve burrows into sandy mud on the seafloor and is caught by dredge net or diving. Once landed, the shell is opened and the meat drawn out, then rubbed with salt to rinse off its slick coating before it is worked. For sushi, the meat is butterflied and finely scored, shaped into a flower-like form while keeping its crunch — a step said to separate a skilled hand from an ordinary one. The himo is often vinegared or dressed separately, prized for a texture distinct from the body.

Enclosed inner bays like Sendai Bay stay calm enough for sandy mud to settle, said to give this bivalve the quiet seabed it favors. Many of its landing sites also sit close to the Edo-style sushi culture's home ground, one reason it is thought to have become a sushi staple rather than mainly a sashimi item. Winter into spring is treated as when the meat fills out and gains the most richness, and the closeness of these calm bays to nearby urban food culture is thought to be one reason the clam came to be treated as a special sushi item rather than an everyday one.