They had a tough, almost leathery skin that was usually a dark gray, green or brown in color. They had angular heads that sloped upwards from a low forehead to the rear of the cranium. The jaw was angled down so that the mouth, which reversed the angular pattern to slope upward away from the line of the jaw and forehead, protruded slightly away from the face. (Star Trek IV: The Voyage Home)
According to that source, the Ariolo had centaur-like torsos, which was eventually revealed in Star Trek: Lower Decks. They were also described as a hedonistic race who are reputed to be the best musicians in the galaxy. They are the only race known to the Federation that has no concept of time.
Their homeworld was called Fillandia, a tidally locked planet that was plagued by earthquakes and volcanoes. It was described as a large, humid world, dominated by tropical forests and mountain ranges.
The Ariolo were mentioned on a plaque affixed to a specimen tank found in the mirror universe's Paul Stamets laboratory aboard the ISS Charon. The tank contained bone tissue samples from this terrestrial species.