Abstract
Morphological, physiological, behavioral, and developmental studies of the mechanosensory lateral line system are used to define sources of morphological and functional variation in the system among fishes (and briefly in amphibians), review patterns and mechanisms of embryonic and postembryonic development, discuss how interspecific variation in morphology is explained by developmental patterns, and place the morphology of the lateral line system in model species for neurophysiological and neuroethological studies into a broader comparative context. The presence of both canal and superficial neuromasts defines two sensory submodalities in jawed fishes. The number and spatial distribution of superficial neuromasts appear to demonstrate more variation among species when compared to that of the canal neuromasts, whose distribution is limited by their association with the lateral line canals. Morphological diversity of the lateral line canal system is defined by (1) variation in the morphology and extent of development of the cranial lateral line canals; (2) the number, placement, and extent of development of the trunk canals; and (3) the distribution of superficial neuromasts on the skin of the head, trunk, and tail. An understanding of the pattern and timing of lateral line development is essential for an appreciation of changes in lateral line function and thus its behavioral roles through a fish’s life history. The evolution of the lateral line system and structure–function relationships among species are best appreciated when patterns and underlying mechanisms of development are considered. Conversely, an appreciation for morphological diversity among species is likely to assist in the interpretation of developmental patterns.