Lamprey larvae are called ammocoetes. The larvae look very different from the adults, and originally they were described as different species -- that's why they have a latin-sounding name. While an adult lampreys may range in size from 10 to 100 cm long, the ammocoetes is only 1-2 cm long. The larvae are anatomically quite simple; eventually they undergo a metamorphosis, reorganizing their bodies and developing into the more-complex adult forms.