Britannica
Sources used in this answer
How does the skull of a flatfish become twisted during metamorphosis?
Created from Britannica articles
using AI.
AI can make mistakes, so verify using Britannica articles.
pleuronectiform
Body plan and sexual dimorphism in the common sole (Solea solea) and dusky flounder (Syacium papillosum).
During the metamorphosis of pleuronectiforms, the skull undergoes significant structural changes to accommodate the migration of one eye to the opposite side of the head. This migration occurs either over the middorsal ridge or through a depression in the head.1
The process involves several key osteological shifts:
- Supraorbital Bar Reabsorption: To allow the eye to pass through the head, the dorsal edge of the supraorbital bar is reabsorbed. These bars eventually ossify to form the interorbital bone.1
- Frontal Bone Shift: The frontal bone on the blind (bottom) side shifts toward the ocular (upper) side, where it contributes to the floor of the optic capsule for the migrating eye.1
- Cranial Torsion: The essential feature of the flatfish skull is the twisting (torsion) of the ethmoid, mouthparts, and frontal bones.1
These transformations result in the characteristic asymmetry of the adult fish, allowing the animal to rest on its side on the ocean floor while maintaining both eyes on the upper surface.21