The Aldebaran serpent was a reptilian lifeform native to the Aldebaran system. It had three semi-transparent cobra-like heads extending from a brilliantly glowing sphere hovering above the ground, surrounded by lights.
In the Q Continuum miniseries, Q turns Picard into an Aldebaran serpent during their initial trip into the past, saying that it was one of his favorite forms before humanoids began to evolve; he claims he did it to create a sense of antiquity. Picard's mind can't handle three viewpoints at once, so Q reluctantly changes him back.
According to the RPG sourcebook Creatures, the Aldebaran serpent lives in the rivers and lagoons of the southern continent of Aldebaran III. It is 2-3 meters long and weighs 80kg. It has a four-lobed brain located in its thorax. All three heads have sensory organs and venomous fangs. Some primitive tribes on Aldebaran III worship Aldebaran serpents as gods.