Thought-gathering in possible preparation for species ref-sheets.
Agriltheans are multi-tentacled demons that range from 6-10 feet/1.8-3m tall. Current agriltheans include Varin and this as-yet unnamed character. Murgatranthes is half-agrilthean, but you wouldn’t really know it to look at her, as her ontos side dominates so much. The way her wings are constructed in what look like ‘layers’ of membrane is similar to that seen on the cowl-like arrangement of an agrilthean’s torso, and Murgatranthes’ chest spikes are something not generally seen on an ontos.
Agriltheans have some bones but a lot of their skeleton is cartilage and segmented chitinous plates that flex with sinews. They are largely soft-bodied and often thought of as fragile for this reason, but they do not seem themselves that way. They would think of bony land-dwellers as fragile because our joints can only bend one way or snap, whereas an agrilthean’s tentacles can entwine any which way without discomfort. They are monocardioids (demons who have a combined heartcore instead of a separate heart and power core).
They are sometimes called ‘arsebrains’ as an insult, but they don’t really understand why it’s meant to be rude. They do have a secondary brain and a more decentralised nervous system than most intelligent beings, and they don’t understand why that’s meant to be a bad thing. (They’ll still be offended if you call them arsebrains because they can tell you’re trying to be rude on purpose, even if they don’t understand why it’s supposed to be rude.)
Agriltheans do not often engage in physical combat. They could rip your limbs off, or bite you, but can’t really kick or punch. They are powerful mages (which is partly why Varin is so shy - its magic is weak).
They can breathe in air, fresh water and salt water. Very young agriltheans find air-breathing a bit difficult, and they shouldn’t be brought out of the water if it can be helped. Some agriltheans live their whole lives and die underwater without ever breaching the surface.
Agrilthean culture is quite disparate from ‘mainstream’ (surface-dwelling) demon culture and there is little overlap. Their language and alphabet has no connection to surface-dwellers’. They have two dialects of their spoken language: the normal one they speak underwater, and a truncated/simplified way of speaking that they use when in air. They can make most human speech sounds without great difficulty (they can’t do rolled Rs, as they have a radula instead of a tongue).
It is impossible for a summoner to form a contract with an agrilthean. They simply won’t. They don’t hate humans particularly (in fact, they will help drowning humans and are often happy to ferry them across bodies of water if asked nicely), but have no interest in working for us. (If you’ve played SMT: Lucifer’s Call/Nocturne, they’re like the demons in the Amala Network and Labyrinth: they’ll talk to you and trade items with you but can’t be recruited.) Of course, a sufficiently powerful summoner could bind an agrilthean to their services by force, but doing that is A Bad Idea.
They are omnivores but can’t digest most land plants - the only plant matter they normally eat is soft weeds. They can eat grapes, but those are just sugar and water anyway. They can eat most land meats. (Varin in particular enjoys ham.) Most of their cuisine is raw because you can’t cook underwater, except for boiling (done with geothermal vents or with magic).
In the past, agriltheans were mostly r-selectors. They laid large clutches of eggs, and left them to manage by themselves. After a couple of years, any young still alive would be taken in, looked after and raised. As the agriltheans evolved sentience and developed civilisation, they decided it was cruel to bring so many young into existence that were doomed to die, so they switched to being more k-selectors. They still lay large clutches of eggs, but as they lack the resources to raise them all, they set aside the ones they judge to be most hale to be raised, and eat the rest before they have a chance to develop. They lay slightly fewer and bigger eggs than they did at the beginning of their recorded history, demonstrating that they are evolving further down the k-selection path.