Disciples- Disciples of Thoon are illithid whom are closest to it's ideals, the movers and shakers. Plotters and schemers. Interpreting and enacting their will.
Shadow Hunter - These are a mutation in the normal illithid breed, skin that is black instead of the usual muave to purple hue, the Shadow Hunters focus on stealth above psionic ability, and as such have less pronounced craniums. They will often follow infiltrators and kidnap targets they've marked.
Infiltrator- A race that was once human, or something else that is now controlled completely by the cult. A bundle of tentacles at the base of their neck. They are the spies among the surface world, gathering information spreading false rumors and finding suitable targets for food, enslavement, or conversion. Often supported by a shadow hunter.
Thrall- Slaves, pure and simple. Often mentally dominated, or infected so disobediance will end rather abruptly. Can often serve as a sort of live stock to breed children to feast on. Though it is not unheard of for them to be trained and serve as guards.