Plesiosaur

The sea monster that did Ganzack's bidding. Sea monster was a massive pleasiosaur. The monster wore a helmet on its head.

Upon first encountering the beast it kidnapped Nami despite Luffy's attempt to eat it. Later it assisted Ganzack in his battle against Luffy. The monster was finally defeated by the islanders who hurled dynamite at it sinking Ganzack's ship in the process.