Britannica
Sources used in this answer
How does torsion change the body arrangement of gastropods?
Created from Britannica articles
using AI.
AI can make mistakes, so verify using Britannica articles.
mollusk
Mollusk shell classification chart, c. 1861.
Torsion is a unique developmental process in gastropods that occurs during the veliger larval stage. It involves a 180° twisting of the body, which shifts the posterior portion of the animal to an anterior position located directly behind the head.1
This anatomical reorganization has significant effects on the gastropod's internal structure:
- Nervous System: The visceral nerve cords, which are bilaterally arranged in primitive forms, are twisted into a figure-eight shape as a result of this rotation.2
- Mantle Cavity: By bringing the posterior part of the body forward, the mantle cavity is repositioned to an anterior location.1
In many advanced gastropods, secondary modifications have occurred to return the body to a more nearly bilateral state, and several groups have undergone a process known as detorsion.2