What changes occur during lamprey metamorphosis?

After approximately three years of development as a blind, wormlike ammocoete larva, the lamprey undergoes a radical metamorphosis to transition into its adult form. During this process, several significant physiological changes occur:

• Sensory and Oral Development: The rudimentary eyes complete their development, and the hoodlike upper lip is transformed into a suctorial oral disk, which allows the adult to attach to hosts.12
• Glandular Transformation: The endostyle, a mucus-secreting organ located in the pharynx used for filter-feeding during the larval stage, changes into a thyroid gland.12
• Physical Growth: The fins along the back increase in height, preparing the animal for its more active adult life.12

Following these changes, many lamprey species migrate to larger bodies of water to begin a parasitic life, while others remain in freshwater environments to mature sexually, reproduce, and die.32