The Nos Monster is a large non-sapient predator found in the sinkholes and underground water bodies of planet Utapau. Nos Monsters have huge eyes in order to see in the darkness of the caverns. They are aggressive creatures, specially when protecting their young.
Evolution
Obi-Wan Kenobi once speculated that the Nos Monster may be a distant relative of the Varactyl, since they're both found in Utapau and share some anatomical characters. It has also been stated that the Nos Monster is closely related to the Swamp Slugs of Dagobah.
It is unknown if the Nos Monster/Varactyl/Swamp Slug common ancestor lived in Utapau or Dagobah. The idea of two closely related organisms in different worlds might support the theory of panspermia.
Behind the scenes
A Nos Monster was originally going to appear in the movie Revenge of the Sith, but the scene was cut, it did, however, appear in the Revenge of the Sith Nintendo video game in 2005.