Sea cucumber is called Namako なまこ / ナマコ in Japanese.
Thinly sliced fresh (raw) sea cucumber is used for a kind of Japanese vinegared food. It is usually served with ponzu sauce (citrus-flavored soy sauce).
It is often topped with grated daikon radish with chili pepper called もみじおろし Momiji-oroshi.
The texture of the sliced sea cucumber is a little tougher than usual seashell.
おつまみなまこ 500 yen
This one is topped with grated daikon radish with chili pepper, chopped green onion and wakame (sea vegetable).
Red Sea Cucumber
Some supermarkets sell fresh sea cucumber in Japan.