The Crustacoids were a crustacean race.
The Crustacoids had crab-like spiny carapaces, green blood, bronze claws instead of hands and feet, and large diaphanous wings which allowed them to fly. They were a long-lived race. (PROSE: Fallen Angel)
A group of Crustacoids, believing they had a divine right to rule, attempted to conquer the universe. The Time Lords incarcerated them in a prison in the 1930s Sussex countryside which resembled an English manor house and was guarded by androids. They made the Crustacoids believe that they were still fighting the war, that the prison was a fortress and the guards their servants. Eventually, the prisoners all killed each other.
In 1933, some time later, the Second Doctor, Jamie McCrimmon and Zoe Heriot arrived at the house, where they were attacked by the androids. The Doctor escaped and, with the help of Lucas Seyton, freed his friends. He then contacted the wardens, asking them to shut down the prison. (PROSE: Fallen Angel)