2016 年 21 巻 1 号 p. 55-64
The taxonomic subdivision of certain Japanese freshwater amphipods into Jesogammarus jesoensis (Schellenberg, 1937), J. hokurikuensis Morino, 1985, J. fujinoi Tomikawa and Morino, 2003, and J. shonaiensis Tomikawa and Morino, 2003 was reassessed using both morphological and molecular data. Putative diagnostic morphological characters did not exhibit consistent geographic distributions, but eight geographically consistent monophyletic clades were detected based on COI and COI+12S rRNA sequence data. Uncorrected COI nucleotide divergences between the clades ranged from 7.0% to 16.4%, a level usually considered to represent inter-specific differences in crustaceans. No morphological features that differentiate the molecular clades were found. While the formal nomenclatural handling of these findings remains a problem for the future, for now we suggest the use of the term “J. jesoensis complex” to represent taxonomic entity consisting of the nominal taxa J. jesoensis, J. fujinoi, J. shonaiensis, and J. hokurikuensis, and potentially a number of hitherto cryptic taxa as well.
