Medusa - Aerocoelenterates

Drifting over the mountaintops of Pandora, these deadly and beautiful creatures look like the alien offspring of a Portuguese Man o' War and an adblimp. During mating season, regions of the southern continent of Australis are blackened by the shadow of the medusa swarm as it swirls in a dance of interlocking tentacles. (Read more)
The medusa's clear membranous sac, or "bell," is filled with hydrogen gas produced by the digestion of its prey. This gas allows the medusa to float above the canopy in search of potential victims.

Their translucent tentacles, which create a kind of curtain sweeping across the terrain, make a faint swishing sound that causes animals to scurry. The tentacles, which are three to eight centimeters in diameter, are replete with sensors that react instantly to the touch of an animal by curling into a vise-like grip. The tentacles are also lined with electrocytes that can channel a current from an organ in the bell that produces electricity. The shock can be strong enough to stun a banshee or kill a full-grown human. Once in the grip of the tough, leathery appendages, it is unlikely that any creature will survive. The tentacles then lift the prey to the medusa's pulpy mouth.

As a defense mechanism, the bell can pulse (much like an octopus) to give some directional control. It expels gas to descend and uses fluids from trim bladders to rise. For the most part, however, the creature is content to drift on the winds and hunt opportunistically.

Their eyes (or, more accurately, their optical sensors) are in a fleshy belt around the bottom of the bell. They provide the animal with a 360-degree view of the terrain beneath them. To look up, they must use extraordinary effort to reorient themselves.

Given their limited mobility, they could become easy prey for other aerial predators, such as stingbats and banshees. But the medusa has little edible flesh. In addition, the unpleasant and potentially dangerous release of hydrogen gas is a natural deterrent to any predator; when the bell is punctured by tooth or claw, the medusa has been observed flying in erratic circles like a punctured balloon, confusing or startling the predator. For these reasons, they are rarely attacked. Its only consistent enemy is the leonopteryx, which, if deprived of food, will on occasion attack and eat the foul-tasting medusa.