This is a submission for the Anatomically Correct Series.
Sandworms are a famous creature in fiction and mythology. Various mythological creatures are the Mongolian Death Worm and the Lambton Worm. For fiction, the movie Tremors is about Sandworms and Dune has the largest and most famous Sandworms.
The largest worm on Earth weighs less than 2 kg so it would be strange for a worm to grow to a massive size. I'm also not sure what a giant worm would eat. It might actually make more sense for a huge worm to evolve from snakes rather than other worms.
Anyway, is it plausible for there to be a huge wormlike creature that lives in the desert and tunnels underground?