So, with that out of the way, lets take a look at the Sandworms as a naturally occurring species in Arrakis as per the commentary of the Dune encyclopedia. For centuries, it was widely believed that the majestic Sandworms of Arrakis were the culprits behind the planet's desertification. However, a shift in scientific understanding led many to reconsider this notion, proposing instead that the sandworms had adapted to the desert environment rather than causing it. So, According to the research after the disappearance of the worms in Arrakis, they came to a conclusion that from the very beginning, the evolution of the sandworm was a remarkable tale of survival and adaptation.
The second one here is the Sandworms as an alien species introduced to Arrakis. This origin story is actually treated as canon since it was teased Early in Frank Herbert’s Children of Dune. Here, Leto II reveals to his twin sister Ghanima, that the ecological change Dune is experiencing will lead to the death and mass extinction of all the sandworms. In the book, Leto said that"'The sandtrout'was introduced here from some other place'" which means that because he had prescient powers, enabling him to see the past, present and future, he was able to see past the written and manipulated history of humanity, he was able to view the actual origins of the sandworms and much of what had happened over the thousands of years.
Now, lastly, with Leto’s statement of the Sandworms being introduced to Arrakis in the past, lets take a look at them as a genetically engineered species. We would have to do investigative work here guys, just as in the real world, we follow the money, here we follow the spice. So, since the spice was said to have been first discovered here in the planet of Dune, that means only one thing and that is, this is an intentional by product of a species genetically engineered for the desert world and made specifically for the conditions of this planet in order to manufacture the much needed compound.