A spiderlike virus attacked the Culture by inserting their DNA into the Culture and turning them into nurseries for incubation of more of the virus.
When the Seventh Doctor arrived on the same planet, he detected the Culture's telepathic distress call. He determined it was coming from a kind of mass mind cell culture in a small dinosaur. When the dinosaur died, the Doctor retrieved a syringe of maxenshudicea from the TARDIS, which killed the virus and saved the Culture. He put the dinosaur's body into the ocean, allowing the Culture to leave so it could continue to live. (COMIC: Culture Shock!)