Serpentine

Serpentine describes any organism or item that possesses characteristics similar to that of a snake or serpent. In science fiction, there are literally hundreds of alien life forms, alien species and exotic animals that possess serpentine features. Life forms that possess tentacles of any kind could also be said to have serpentine qualities.

Examples
In the Star Wars mythos, Luke Skywalker is attacked by an animal called a dianoga in the trash compactor of the first Death Star in Star Wars Episode IV: A New Hope. While the dianoga appeared to be serpentine at first, later depictions reveal it to be a vertebrate animal with several tentacles.

In Star Wars Episode V: The Empire Strikes Back, Luke and R2-D2 land on the swamp planet of Dagobah. A dragonsnake is briefly seen skimming the surface of a bog before momentarily snacking on R2-D2 (he spits him out moments later).

The head tentacles of the Twi'lek race, known as lekku, could be construed as being serpentine.

In the Stargate film and television franchise, the main antagonists of the series are an alien race known as the Goa'uld. The Goa'uld are parasitic in nature, requiring a human host form to carry their serpentine bodies. Goa'uld in their natural states, without a host, are non-arthropod invertebrates approximately 8"-12" in length.