Most of the film depicts the monsters as carnivorous worms or tentacles, which emerge from the water to suck the flesh from their victims' bones. During the climax, the heroes discover that the tentacles all stem from one single creature: a gigantic, octopuslike sea monster squatting in the center of the ship. According to "Deep Rising" mythology, the monster came from the bottom of the ocean, in a deep trench never explored by man.
At one point in "Deep Rising," the antagonist speculates that the sea monster may belong to the Ottoia family: prehistoric deep sea worms that used spines or teeth to "drink" their victims. Ottoia worms thrived during the early Cambrian era, in the Burgess Shale near British Columbia, Canada. The actual creatures were much smaller than the monster depicted in the film.
When the sea monster finally appears, it actually resembles an upright cephalopod more than a sea worm. Cephalopods include marine mollusks, such as octopi, squid and cuttlefish. Like other cephalopods, the sea monster possesses tentacles and a flexible internal structure, allowing it to squeeze through narrow cracks. Cephalopods also share basic feeding habits with the sea monster: using digestive juices to separate the flesh of their prey from the shell or bone, then ejecting the indigestible components and moving on.
Though essentially a horror/comedy, "Deep Rising" owes a debt to a much darker tradition of horror. In the 1920s, author H.P. Lovecraft created a group of monsters who dwelled deep under the sea or in the depths of space: not strictly evil, but so alien and unworldly that concepts of morality did not apply to them. The universe reflected their sensibilities far more than the sensibilities of people, and the implications of their existence were enough to drive men mad. Lovecraft's work signaled a transition from older Romantic traditions of horror to more modern, existentialist sensibilities. The creators of "Deep Rising" used his works as inspiration for their monster, which bears a close resemblance to many of Lovecraft's creations.