After the expedition base was found, and the professor, along with his anti-matter minerals, brought on board, the ship tried to take off, but was unable to as the anti-matter creature prevented its escape.
The Fourth Doctor warned that he minerals had to be returned so Morelli and De Haan were tasked with taking them off the ship. While getting rid of the last of them, Morelli was attacked and killed by Sorenson, who had been infected by the anti-matter. His desiccated corpse was discovered by De Haan. (TV: Planet of Evil)