Seugathi were created by Paizo Inc in 2008, appearing in the Denizens of the Darklands sourcebook for the Pathfinder RPG.
The Seugathi are huge creatures, that resemble a cross between a worm and a caterpillar. Having bodies that stretch up to 14 ft in length. When threatened a Seugathi will rear up, using their caterpillar-like legs to support themselves. On their heads are three sharp bony jacks and insectoid eyes. At the end of the body, the torso splits into two long prehensile slender tentacles which are used to wield weapons.
It's a subterranean race of sentient tentacled worms that serve the Neothelids who spawn hundreds of them in pits. Only a ft long when spawned, the begin to consume each other, until only one fully grown adult remains. At which time, the Neothelids begin to give it many missions which further the secret agendas of their makers. Each Seugathi is spawned for a single purpose.
While they are able to survive on subterranean fungus and creatures, a Seugathi's favorite food is the rational thoughts of the sane. Unfortunately for the victim, the siphoning of those thoughts drives them insane. Seugathi bites are also poisonous which makes the victim more pliable for feeding. Lonely creatures which rarely interact with other lifeforms, though they occasionally are encountered in small groups of their own kind which are known as cults or being led by creatures of a similar mindset.