Skarasen

Skarasen were large creatures whom the Zygons relied upon for milk and their destructive capabilities.
== Biology ==
The Skarasen were massive creatures, large enough to crush a human with one clawed foot. They were cybernetically altered to suit the Zygons' purposes, and were vulnerable to no force short of a nuclear weapon. Their skins were highly durable, and their skeletons were fused with an extremely tough alloy. 
Zygons fed on the milk of the Skarasen. This milk, resembling a green ooze, was vital to the Zygons' survival. 
Skarasen swam so fast that they were able to swim around the world in the space of a week. 
== History ==
Originally from the Zygon homeworld, a large number of Zygons transported embryonic Skarasen to Earth in their ships, and the Skarasen were cybernetically enhanced to be weapons. The modifications to the Skarasen were so extensive that the Zygons could see through their eyes via monitor screens.
The group of Zygons who came to Earth in the 12th century brought a Skarasen with them. The Skarasen attacked any persons or objects to which the Zygons attached a transceiver that broadcasted an ultrasonic emulated mating call to the Skarasen. The Skarasen's presence in Loch Ness had helped to inspire the local legends of the Loch Ness Monster. 
In 1894 in London, the Eighth Doctor encountered a group of Zygons and Skarasen babies. The Doctor (after nearly killing many of them by accident) helped the remaining Zygons move the baby Skarasen to an uninhabited planet to begin a colony. 
In 1909, another group of Zygons came to Earth. Though they had brought two Skarasen, their minds were damaged by the solar radiation brought on during the destruction of Zygor and one was killed during the attempt to repair the damage. The other one was cured by the Tenth Doctor and was allowed to escape after devouring Brelarn. 
In the mid-20th century, UNIT began investigating Loch Ness, so the Zygons sent out their Skarasen. Following the Fourth Doctor, who had a homing device in his pocket, the Skarasen travelled from Loch Ness to London via the Thames. The Doctor threw the homing device out for the Skarasen to fetch. Its subsequent fate remained unknown, though with the death of the Zygons on Earth it would have had no-one left to control it. The Doctor stated it went back to Loch Ness, the only home it had ever known. The event was covered up, with it being claimed that the monster was merely an inflatable protest tool. 
An incarnation of the Master owned a Skarasen named Flipper, and kept the creature in a tank in his TARDIS. The Master used to feed allies and enemies alike to the creature, either because they'd outlived their usefulness, or because they were annoying him. Flipper met a rather ironic end when it was ultimately killed and barbecued by the Master, who had grown tired of his pet.