“Torigai” does not have a real name in English. They are approximately translated “large cockle”
They appear on the market in Spring and earlier in Shizuoka Prefecture. They are mainly found in Tokyo Bay, Ise bay and Seto Inner Sea. Some are imported from Korea, but catches can wildly vary, especially with the occurence of “red tides”. A lot are imported from Aichi Prefecture to Shizuoka.

They must be absolutely fresh to be consumed.
One easy way to check if they are still fresh is to slam them on the wooden board. They shouldimmediately retract, even if cut out. They are at their cheapest between March and May.