Halichondria is a genus of marine demosponges belonging to the family Halichondriidae.These are massive, amorphous sponges with clearly separated inner and outer skeletons consisting of bundles of spicules arranged in a seemingly random pattern. This genus of sponges became important through the discovery of cell division limiting properties of the extract Halichondrin B, which inhibits cell mitosis. The drug Eribulin, a related compound and an inhibitor of microtubule function, has become an important chemotherapy treatment for certain types of cancer.