Pen Shells or Tairagi in Japanese are usually sold in winter but tend to still appear in Sping in Shizuoka.
Also called Tairagai, it was very common not so long ago when the domestic catch amounted to 13,395 tonnes in 1976 to suddenly fall to a mere 134 tonnes in 1994!
It disappeared from the Tokyo Bay and is presently mainly caught in the Inner Japanese Sea between Shikoku and Honshu Islands.
It has become expensive these days and when you realize there is not so much to eat for such a big shell, one can understand it is fast becoming a rare morsel.
It is particularly delicious as sashimi or salt-grilled and is very similar to scallops, although distinctly different in shape.
Naturally it is most popular served as sushi nigiri!