A jawless fish, which lays eggs in fresh water and whose ammocoetes larvae after metamorpho sis return to the ocean is (a) Neomyxine (b) Petromyzon (c) Eptatretus (d) Myxine.
Option B.Petromyzon (Lamprey) belongs to the Class Cyclostomata of PhylumChordata. It is a jawless fish which lays eggs in fresh water. The eggs hatch in about 3 weeks into minute transparent larvae called ammocoetes. After metamorphosis, the young lam preys swim down to the sea where they remain for 3 or 4 years before reaching maturity, when they once again migrate to streams or rivers to spawn and die. Gonads become mature at that time when adults re turn to rivers for spawning.
