Zaralok

Zaraloks are giant shark-like aliens that are present in the Doctor Who PC game: Shadows of the Vashta Nerada.

Phisiology
Zaraloks are fifty-foot-long, shark-like aliens with two separate caudal fins and armour plating reminiscent of placoderm fish such as the Dunkleosteus. Zaraloks can withstand immense pressures and are extremely fast and flexible, as well as possess the ability to see through dim waters because of their large eyes.

Origins
Zaraloks were bred by an aquatic race of aliens known as the Valky Clan on the planet Shakara as a weapon in an undersea war. Unfortunately, the Zaraloks overpowered the control of the Valky Clan and turned against them, killing both the Valky Clan as well as their opposing enemy.

"Shadows of the Vashta Nerada"
One of the Zaraloks arrives on Earth due to a temporal rift in the 23th century and started attacking the Poseidon 8 undersea city. It was later sent back to Shakara by The Doctor and his companion Amy Pond.