The lateral line system and its innervation were examined in two paedomorphic species of Apogonidae, Gymnapogon japonicus and Pseudamiops cf. springeri, both of which have been included in Gymnapogonini (Apogoninae) characterized by a small translucent body lacking canalized lateral line scales, but with many superficial neuromasts (total SNs: 2,691 and 2,197 in G. japonicus and Pseudamiops cf. springeri, respectively). Although scales are entirely absent in G. japonicus, the innervation pattern of the trunk lateral line system is basically similar to that in other apogonids having a single lateral line scale series. In comparison, Pseudamiops cf. springeri (and P. gracilicauda) have three series of inconspicuous lateral line scales with a distinct innervation pattern, implying a phylogenetic affinity with Pseudamia (Pseudamiinae). The monophyly of Pseudamiops and Pseudamia was also supported strongly by a molecular phylogenetic analysis, thus the paedomorphic nature is considered homoplasy between Pseudamiops and Gymnapogon. The innervation of head lateral line system in G. japonicus and Pseudamiops cf. springeri is basically the same with that of other apogonids, supporting homology of the presence of many head SNs among the species. The SN pattern and head canals of adult Pseudamiops cf. springeri are similar to those in juvenile Pseudamia gelatinosa, implying a paedomorphic truncation of lateral line system development in Pseudamiops cf. springeri.
Keywords: fishes; lateral line nerve; neuromasts; phylogeny.
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