Bonellia viridis are a species from the Bonellidae family, within the Echiurans. 

They are small cryptic animals, living in burrows inside rock boulders and are therefore hard to come across.
They have a cylindrical trunk and a long green proboscis due to the production of bonellin, a toxin active not only on prokariotic but also on eukaryotic cells (Agius et al, 1979). The proboscis is highly muscularized and heavily ciliated. As they are deposit feeders, their digestive system is very long and specialized. 
Sexual dimorphism is very high in this species as the females can measure up to 8 cm and males only 1 to 3 mm.  Their mode of reproduction is particular, as the male lives inside the female and fertilizes the eggs when necessary. 


Photo by Lucie Malard