On this blog, a response posting from one Michael Rooney makes the claim (05/10/2019)
[The nature of the Intellect Devourer] was reshaped by Dave Trampier’s art. If you read the original description (in the little brown books—most of which is the same as the 1e MM’s), there’s nothing about it looking like a brain, only the legs are described. That’s because the original monster is an emulation of the gebbeth in LeGuin’s A Wizard of Earthsea: a taloned, faceless thing that possesses its victims’ bodies. Interestingly, LeGuin got the idea for a gebbeth after looking at a microscopic tardigrade (the water bear), with its hook-like legs and no head.
Apart from this quote (and another citing it), I haven’t found any references on the internet connecting Intellect Devourers to gebbeth, and I haven’t read Earthsea.
Does anyone have a source confirming or refuting this?
Related: Do Intellect Devourers need to Eat?
Related: Were Illithids inspired by Cthulu?