The Pyxians were a race of telepathic creatures that were able to use mind-boosters, projecting an artificial reality—like in holosuites—though the experience was still real to those involved in the illusion. They were quite powerful at projecting illusions, able to even project replicas of themselves across many light-years, even through a wormhole.
Pyxians were a metamorphological species, young Pyxians resemble a rhino covered with golden fur the size of a dog. This stage of their form was called Solitary. Eventually the young will wrap a cocoon around itself, and emerge as a humanoid Pyxian. (DS9 novel: The Pet)
The Pyxians were a isolationist people, as their only real defense was their ability to camouflage, direct contact of any kind makes them vulnerable. Thus they refrain from making contact with other races at all costs. (DS9 novel: The Pet)