Observations on the development of the lateral line system in the Pacific hagfish (Eptatretus stouti, Myxinoidea).

We investigated the development of the lateral line system of the Pacific hagfish, Eptatretus stouti, using three-dimensional reconstructions from serial sections. Adult hagfishes possess a number of densely innervated skin grooves of unknown function, and these grooves do not contain typical lateral line receptors (i.e. neuromasts). However, three separate lateral line placodes appear to be present during development and these placodes give rise to groups of neuromast primordia. Unlike in other craniates, the neuromast primordia do not develop into neuromasts, but they apparently transform into the skin grooves of adults.