The normal Sand Worm is by far the most prevelent of its kind and certainly typical in appearance. It appears as to have a sand colored back and body but a soft under side that can be attacked for critical damage. Frequently, they appear in small groups of at least two or more. When they appear, they'll come out of the sand and attack with a ranged spitting attack. They will maintain this attack until you get too close to them at which point they will burrow under the ground rather than continue to fight. At that point, they will find somewhere else to come out of the sands and continue their attack.
They are not particularly strong on their own but in large groups, they can be quite dangerous.