Big and ugly and thankfully legendary/imaginary :) I have a feeling the sand thingies in Dune were based on the cryptid legend, there's a page of information — and very unpretty pictures — https://allthatsinteresting.com/mongolian-death-worm (URL).

My imaginary version is a miniature one so not as completely deadly... I've got this picture (https://static.wikia.nocookie.net/cryptidz/images/f/f0/Death_worm_5.jpg) in my head, but may change it later (maybe merge it with a medieval dragon picture, I love them). I do wish I could draw...