Halichondria is a genus of sea sponges 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.

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