Green Spoonworm

Overview

The Green Spoonworm (Bonellia viridis) is a unique marine worm known for its extreme sexual dimorphism and the production of a toxic green pigment called bonellin. While the plump, green females are often hidden within rocky crevices or burrows, they are easily identified by their remarkably long, extensible, and forked proboscis that sweeps the seafloor for food.

Appearance

Adult females possess a soft, sausage-shaped body typically measuring 5 to 15 cm in length, which is often covered in small papillae. Their most striking feature is a highly extensible proboscis that can reach over 1 meter in length and features a characteristic T-shaped or bifid tip. In contrast, males are microscopic, measuring only 1 to 3 mm, and lack the complex structures of the female, appearing as simple, ciliated, unpigmented organisms.

Distribution & habitat

This species is widely distributed across the Mediterranean Sea, where it is common in shallow coastal waters, and is also found in the Northeast Atlantic, ranging from the Canary Islands to Norway. They primarily inhabit hard-bottom substrates, such as rock crevices, holes, or abandoned burrows, where they remain concealed while extending their proboscis into the surrounding water.

Feeding

Acting like a biological vacuum cleaner, the female uses its long, ciliated proboscis to collect organic detritus, microorganisms, and small particles from the seafloor. The proboscis traps these food items in mucus and transports them back to the mouth.

Reproduction

Bonellia viridis exhibits a fascinating environmental sex determination system. Larvae are initially undifferentiated; those that settle on the seafloor develop into females, while those that come into contact with a female's proboscis are triggered by chemical cues to develop into dwarf males. These males then live as parasites within the female's reproductive tract to fertilize her eggs.