Bonellia

worm

Written by

The Information Architects of Encyclopaedia Britannica

Last updated

June 17, 2026

Quick Summary

The genus Bonellia refers to a type of marine worm belonging to the phylum Echiurida, also known as spoonworms. These worms are characterized by a sausage-shaped body and a distinctive, scoop-like proboscis used for collecting food.1

A unique aspect of Bonellia is its extreme sexual dimorphism and unusual sex determination. Larvae that settle on the sea floor develop into large females, while those that settle on a mature female's proboscis become tiny, parasitic males. This sex determination is influenced by environmental factors, such as carbon dioxide levels. The males live within a modified organ of the female and are permanently attached.231

Summary created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

3 Britannica Sources

Ask Britannica AI about this topic

Britannica doesn't have a full article on this topic, so we've curated a list of our relevant coverage.

sex
Effects of environment
In the case of Bonellia, a unique kind of marine worm, all eggs develop into small larvae of a sexually indifferent kind. Those that settle freely on the sea floor grow into comparatively large females, each of which has a long, broad extension, the proboscis, at its front end.…
Read More
In the case of Bonellia, a unique kind of marine worm, all eggs develop into small larvae of a sexually indifferent kind. Those that settle freely on the sea floor grow into comparatively large females, each of which has a long, broad extension, the proboscis, at its front end.…
Read More