In Dune, there is not really any actual aliens, but there is something much more interesting. Humankind seems to have branched off into subspecies. I'm not sure if this is what they are, but there are very distinct groups of humans that have special abilities (mutations?). They include the Bene Tleilaxu (a. k. a. Face Dancers), the Fremen, the Guild Navigators, and, to some extent the Bene Gesserit. The Bene Tleilaxu, aptly nicknamed Face Dancers, are able to change shape at will, including shifting between genders. They can succesfully imitate a person both physically and in things like tone of voice or way of speaking. The Guild Navigators are taking a constant supply of melange, a type of drug which allows them limited prescience, but more importantly gives them the ability to safely navigate through another dimension that allows faster than light travel without crashing into a star or planet. I don't know this for a fact, but I think this has caused the extensive physical mutations that guild navigators have. They are described as having flippers, but not much else is known about the Navigators of the Spacing Guild.

The Bene Gesserit and the Fremen fall into another catagory, blurring the line between human but not extensively so. The Bene Gesserit are mostly females, but not all. They have commanded precise control of their nerves and muscles to the point where instinct does not exist and they can beat anyone in martial arts. Bene Gesserit training also controls the mind. It sharpens it to a very precise tool, to be shaped in any way it is needed. Only use machines to complement the tool of the mind, is the Bene Gesserit saying. The Bene Gesserit are not really a new branch of humanity, because anyone can become a Bene Gesserit given the proper training. The Fremen are in a way like the Bene Gesserit, but instead of controlling the mind and body they have controlled their adaption. Fremem live on the desert planet of Dune, soon to become Arrakis, a lush and green planet, and soon after that to become a barren desert again, called Rakis. Fremem have adapted to this climate amazingly. They control their water use with devices called stillsuits, which recycle all of the body's moisture. They also have small mutations that do things like heal cuts quickly so as not to waste water. Fremen children are trained to preserve their body's moisture before they can even walk.

Dune provides a nice break from the conventional aliens seen in SciFi series. I think this is a very interesting book series, and very different from other SciFi series.