Green spoonworm

At the edge of a fissure, a long dark-green shape moves slowly over the sediment. Its extremity divides into two lobes that search the bottom. At first glance, you might think the entire animal is moving in front of you. In reality, you see almost only its proboscis: the female's body remains hidden in the rock.

This proboscis is used to collect food particles, which are then transported to the mouth thanks to cilia and contractions of the organ.

But the most astonishing part of its story plays out well before the dive. In Bonellia viridis, an as-yet-undifferentiated larva can follow two very different destinies. If it develops far from a female, it most often becomes a female. If it is exposed to substances produced by a female, it generally becomes a minuscule male. The mechanism is not absolute, but the female’s influence is solidly demonstrated.

And the contrast is spectacular: while the female reaches several centimeters, the male measures only about 1 to 3 mm. After settling on her, it can live associated with her organism.

Meanwhile, under your eyes, only the large green proboscis continues to explore the bottom. Even if it is lost, it can regenerate. In the dim light of the crevice, the bonellia remains hidden, and only its long green hand seems to seek its way in the sea.