Cractid
From Tardis Wiki, the free Doctor Who reference
The Cracitds were a crustacean species which originated on the planet Helheim.
Biology
The Cractids were crustaceans with an exoskeleton, two claws, six legs, and mandibles. They were the only organism in the entire galaxy which had an immunity to Richter's Syndrome.
A swarm of Cractids could consume a human being — flesh and bone — in under a minute.
The only way to stop them was a sonic burst at the resonant frequency of the Cractids' outer shells it knocked them out for a few minutes.
History
As the Cractids were the only species with an immunity to Richter's Syndrome, Genetech set up a research facility on Helheim and experimented on them to find a cure. (AUDIO: Cobwebs)
