Petrasyls are floating, jellyfish-like creatures that appear in Metroid Prime Hunters.
Petrasyls are capable of living in a variety of extreme environments throughout the Tetra Galaxy, from the volcanic caverns of Alinos to the icy drifts of Arcterra. They are usually found in a group of two or more of their own kind. They are easy to kill and will perish from as little as two shots from Samus's Power Beam, making them easy targets for collecting ammo and energy. However, Petrasyls will continue to spawn no matter how many Samus manages to slaughter.
They bear a striking similarity to Metroids and Mochtroids, but upon closer inspection are revealed to be more like Earth's jellyfish, having tentacles rather than talons. In addition, they also lack the ability to drain energy from other organisms, and instead rely on toxins they excrete that can burn through most materials. However, they are passive in nature, and prefer to hover around aimlessly in large groups, attacking only if touched.
They always fly in a simple pattern, mostly round or rectangular. Some Petrasyls, especially in the Thermal Vast, will fly around without a clear pattern, although they will fall into repetition after some time.
The first Petrasyl is encountered in the Meditation Room of the Celestial Archives. This Petrasyl will always drop Missile Ammo when killed, allowing Samus to load her Missile Launcher and open the door's Brown Blast Shield.
Metroid Prime Hunters
Harmless from a distance. This airborne creature secretes a corrosive toxin that can burn through all but the toughest materials on contact.