Those were creeping crawlers from Space!
After a short search, the submarine brings both the shark and the octopus to an ice trench off the Alaskan coast, where MacNeil first encountered the creatures. Sanders himself ends up piloting the sub after the original pilot loses his nerve and pulls a gun on the captain (Dean Kreyling) before he is overtaken. The octopus and shark begin to fight, but they separate and the shark attacks the submarine, dragging it in its mouth. MacNeil, Sanders and Baxter man a mini-submarine and detach just as the shark bites the larger submarine in half, killing the rest of the crew.
The shark nearly destroys the mini-submarine, but they are saved when a Japanese sub manned by Shimada fires torpedoes at it. The octopus entangles the Japanese submarine and nearly destroys it, but the sub is released after the octopus is attacked by the shark. The two creatures engage in a fierce battle, which ends with both being killed.
The film ends with MacNeil, Sanders and Shimada deciding to visit the North Sea after receiving infrared images of mysterious organic life there.