From Lexicanum

Planetary Summary

Map	Basic Data		Planetary Image
	Name:	Malvolion
	Segmentum:	Unknown
	Sector:	Unknown
	Subsector:	Unknown
	System:	Unknown
	Population:	N/A
	Affiliation:	N/A
	Class:	Dead World
	Tithe Grade:	N/A

History

Malvolion was an Agri World whose inhabitants, after finding a Tyranid beacon on their planet, sent for the Imperial Guard, who indeed came in the form of the Mordian Iron Guard and a tank regiment. They could not however, save the planet. Even as the evacuation was underway, a sudden outbreak of Genestealers and Lictors sent the planet into a panic before, only minutes later, a full scale invasion was taking place. Even the belated intervention of the Lamenters Space Marines was not nearly enough to stop the plague, and the barren world now stands as yet another symbol of the Great Devourer and his mighty fleets.

Source

http://uk.games-workshop.com/tyranids/malvolion/