"Parasite," a 3-D thrill-an-hour film, is built around one single bit from the immensely successful sci-fi thriller, "Alien." You know the bit: What starts out as an Alka-Seltzer upset grows into a stomach-bursting bug with extremely sharp teeth. In "Alien," it was shocking and scary; in "Parasite," it's laughable.

"Parasite" seems assembled from an abandoned serial--there are quick fades and scene jumps that make absolutely no sense. The plot (let's be generous) is set in the future after "all that atomic s--- started dropping out of the sky." An intrepid scientist (Robert Glaudini) is on the run from The Merchants, who want the parasites he's developed and absconded with in a fit of conscience. He's got one in a container and one, kangaroo-like, in his stomach. The scientist hides in a semi-ghost town while he tries to find a cure.

"It's a nice place," says the town's hotel owner (Vivian Blaine). "We've got electricity from 7 to 9." "Nobody's filled up their car with gas in years," adds a wide-eyed gas-station attendant. A waiter recites the menu: "Canned fruit, canned beer and canned soup."

The scientist encounters a natty, nasty Man-from-Glad type who drives the noisiest car in Futureworld. The teen crazies (including ex-Runaway vocalist Cherie Currie) are really dissolute: After the captive parasite turns the tables on one of their number, they just sit casually around the old campfire watching the beast, who they cover with a blanket.

For contrast, there's a nice girl (Demi Moore, a chubby Margot Kidder sound-alike) and her father figure (James Davidson). There is only one sequence that benefits from the 3-D process; everything else is so badly shot that the optical illusion is lost. The parasite, who looks like a Slinky covered in green Naugahyde and whose appearances may total one minute of screen time, can't act, either. One wishes the filmmakers had dulled his teeth and sharpened their wits.