Ankoro

Ankoro is a gigantic anglerfish under the command of captain Vander Decken IX, residing in the Underworld of the Sea, 7000 meters underneath the ocean surface. Wadatsumi seems to regard Ankoro as a pet and told it "not to eat ships" in chapter 606 /episode 525.

History
It tried to eat the Straw Hat Pirates and their ship, the Thousand Sunny, but was stopped by Wadatsumi.

Ankoro was later seen again when Vander Decken IX was talking to Wadatsumi about Shirahoshi.

Trivia

 * Its name comes from "ankō" (アンコウ), the Japanese word for anglerfish.