Category: Kai (shellfish).
Season: Winter and early spring.
Funnily enough, the actual name of this shellfish is baka-gai, which translates to idiot clam. The flesh of the clam is eatable, as are the adductor muscles which are called kobashira. The clam is removed from its shell, rinsed in hot water, then quickly chilled in ice water before being butterflied. It is served with its foot intact and sticking up in the air, as seen in the image above.
Aoyagi has been a favorite since the Edo period, and continues to appeal to sushi fans today thanks to its crunchy texture and sweet flavor.