The Hanonian land eel was a giant serpentine lifeform native to Hanon IV. Predatory in nature, it inhabited mountainous caverns and ambushed prey that approached its lair, leaving their bones piled at the cave entrances.
When the crew of the USS Voyager was stranded on Hanon IV in 2373, a Hanonian land eel killed Ensign Hogan when he attempted to collect some bones near the cave. Later, a number of Voyager crew escaped from a group of pursuing native humanoids by entering the cave of a land eel, and although they did lose another crew member to the eel, the rest narrowly avoided being eaten in the process. (VOY: "Basics, Part II")
The Voth scientist, Forra Gegen searched the lair of the Hanonian land eel almost a year later, looking to get genetic evidence to support his Distant Origin Theory from Hogan's remains. (VOY: "Distant Origin")
The Hanonian land eel was the first alien lifeform on Star Trek: Voyager to be generated entirely by CGI techniques. Prior to using this method, however, visual effects producer Dan Curry drew conceptual art of the creature, finalized in March 1993, one example of which refers to the creature simply as "tunnel dweller." A maquette of the beast was also created. Regarding the process of designing the Hanonian land eel, Dan Curry remembered, "The script called for a creature that lived in the tunnels and was always hungry [....] Whenever I design creatures, I try to use [the] Darwinian approach where, 'What's its environment? What would it need, to exist in that environment?' So, since it was a cave-dweller, I thought it would be cool if it had certain eel-like properties - that was very voracious and had a big mouth - but gave it radically symmetrical appendages, like big claws, so it could kind of scramble up tubes. And like a puffer fish, that it would have air bladders, that it could squeeze itself into a tube and fill it, so it could kind of hang out there or contract itself, so it could go forward." (VOY Season 3 DVD special feature, "Red Alert: Amazing Visual Effects")
The Hanonian land eel was built at Foundation Imaging for Voyager's second season finale, "Basics, Part I", and was that company's first production association with Star Trek. John Teska's creation was such that Curry became convinced that Foundation was up to the task of providing CGI for the series. From VOY: "The Swarm" onward, Foundation became the regular CGI supplier for Star Trek: Voyager. (Star Trek: The Magazine Volume 1, Issue 6, p. 46)