Gaseous, energy-based beings once tormented by Q, who attacked the Enterprise to take revenge on him after he lost his powers.
The Calamarain are beings made of ionized gas, moving through space as a swirling cloud of energy. They are capable of passing through a starship's shields when those shields are lowered, and they hold grudges against those who have wronged them.
In Déjà Q, Q took refuge aboard the Enterprise after the Continuum made him mortal, and the Calamarain came for him. Data was injured protecting Q during one attack. Q's decision to leave the ship in a shuttle to spare the crew led the Continuum to restore his powers.