Shellfish
Ark shell mantle (Akagai himo)
【Nigiri sushi: Kai】
The Ark shell mantle (Akagai himo) is a part of the shellfish that has a rich flavor distinct from the meat itself. Because it has a strong aroma and umami unique to the Ark shell (Akagai), as well as a distinctive taste, some people may find its flavor slightly unusual at first. However, once they become accustomed to it, this unique flavor can become highly appealing.
The color of the Akagai mantle varies significantly depending on its freshness. When freshly removed from the shell, it has a vivid red color, but as time passes, the color gradually darkens. One reason for this is the hemoglobin-based respiratory pigment contained in the Akagai’s hemolymph. This pigment gives the Akagai its characteristic red appearance, and its color changes over time due to factors such as variations in oxygen levels and tissue oxidation.
In contrast, shellfish such as hotate (scallop) and mirugai (Keen's gaper) do not have hemolymph containing such a vivid red pigment, so changes in their color are less noticeable.
Although the mantles of hokkigai (Sakhalin surf clam) and hotate are sometimes served at sushi restaurants, they are not particularly well known and are not generally regarded as standard sushi toppings.
By contrast, Akagai mantle is often highly valued for its stronger aroma and umami flavor compared with the meat itself. Its crunchy texture also makes it exceptionally well suited for nigiri sushi. It is a versatile and appealing part that can be prepared in various ways, including as nigiri, placed between the meat and the sushi rice, or used in rolls.
【Related contents】
Ark shell mantle and cucumber roll (Himokyu maki)
List of Shellfish (Kai)
(Updated July 23, 2026)