Sensory systems and behavior of premetamorphic and metamorphic leptocephalous larvae.

The superorder Elopomorpha (orders Anguilliformes, Elopiformes and Notacanthiformes) is characterized by the presence of a unique larval stage termed the leptocephalus. The basic morphology, chemical composition, developmental pattern, and behavior of premetamorphic and metamorphic leptocephali are reviewed. The eyes, olfactory organs and pores of the lateral-line system are well developed, suggesting that these sensory structures play an important role in larval behavior. Premetamorphic larvae are pelagic and in some elopomorphs subsequent development is associated with migration to coastal waters where metamorphosis takes place. The factors controlling onshore migration, as well as the metamorphic trigger(s), are unknown. The possible relationships between sensory systems and behavioral changes during the different phases of larval development are presented.