Large Seashell (Quest Closed)

Depending on which one you open, you will be rewarded with Some Broken Shells (Item), a Fishbone and two Fish, or a Sea Ear. It can also give you nothing or spawn a Crab.
It will turn into a Large Seashell (Quest Open) upon opening.
Looks the same as a Large Seashell (Closed) and a Seashell (Large).
Part of the Twenty Miles Beneath the Sea Quest.