The Common Sea Squirt or Hoya in Japanese, very often called Sea Cucumber is neither a coral, seaweed, shellfish or whatever. It is an animal of its own class. In its natural habitat, You have to cut it open to reach its edible part.
It can be eaten raw, slightly boiled or pickled. It is said to be the rare sea animal combining the four tastes: sweetness, saltiness, sourness and acidity.