9. Japanese Spider Crab
The Japanese Spider Crab is one of the freakiest sea creatures to date. First and foremost, it is important to note that this is a real crab that you can likely see at some zoos. If not, you can visit the coasts of a few Asian territories like Japan where you can likely come across some of them.
The name of the crab comes honestly, as the legs of the crab look just like regular crab legs. Except for the weird fact that they are insanely long. This makes them come off as spider-like, hence the Spider Crab name. They are horrifying sea monsters to most just based on appearance. However, they are unlikely to go after humans.