Oysters are never served as nigiri; they don't pair well with vinegared sushi rice. However, sushi shops do occasionally serve them as an appetizer. Pictured above are a couple of Kumamoto oysters from Gintei. The Kumamoto varietal originated on Kyushu and made its way to the US after WWII. Strangely enough, they are now very popular in the US, but rarely consumed in Japan. They're small in size, with mild brininess and a sweet finish.