Alien (The Faculty)

These Aliens are aquatic creatures able to control humans. They left their homeworld after it started to die and search for a new planet which they could take control.

History
This alien species lived on a planet composed entirely of oceans. For unknown reasons, their planet started to die, so they decided to go to Earth and to take control of it.

They arrived in a small town in Ohio called Herrington and infected the professors of the local High School, then the students and later everyone in the town.

However, a group of students not infected managed to kill the Queen of the aliens with a diuretic drug, which killed all the aliens simultaneously.

Biology
The Aliens are very similar to fishes or tadpoles in appearence, but they also possess tentacles. Though they are aquatic, they can live out of water if they hydrate regularly. Much like insects, they have a Queen and are connected telepathically to her, meaning that if she dies, all the other Aliens die too.

Queen
The Queen is much bigger than the other Aliens, and her appearance is a lot more monstrous. She is also much more strong and powerful.

Abilities
Their most notable ability is to control humans by entering into their ears. When they control humans, they apparently conserved their memories but their personality changed completely (for exemple, a shy and inhibited person become more outgoing and outspoken, and a brash and domineering person become more understanding and compassionate).

They are also able to duplicate themselves, and they possess limited shapeshifting abilities.

In addition, they are practically immortals since they can survive even if they are cut into pieces. Even in human hosts they possess impressive regenerative powers, they are able to re-attach the host's limbs if they are cut off and can also survive to bullets and decapitations.

Naturally, they are excellent swimmers.

Queens
The Queens possess greater shapeshifting abilities, they can even change their size and turn into human. They are also able to give birth to many Aliens simultaneously and they have colossal strenght.

Weaknesses
These Aliens can't survive without water, therefore they constantly need to hydrate when they are in human bodies. If their host is too old or ill, he eventually dies from dehydration. But their more notable weaknesses are the diuretic drugs, which are lethal for them.