Bonellia viridis, the green spoonworm, is a marine worm (class Polychaeta, phylum Annelida) noted for displaying exceptional sexual dimorphism and for the biocidal properties of a pigment in its skin.

This chemical, concentrated mostly in the proboscis, is highly toxic to other organisms, capable of paralyzing small animals.

In the presence of light, bonellin is a very effective biocide, killing bacteria, larva of other organisms, and red blood cells in laboratory tests.

Most larvae, however, come in contact with the bonellin in the skin of an adult female—its body or its roving, bonellin-rich proboscis—and are masculinised by this exposure.

This environmental sex determination helps green spoonworm populations respond to the availability of burrows.