Abstract
Two Japanese codling Physiculus japonicus Hilgendorf, 1879 and P. maximowiczi (Herzenstein, 1896) have been suspected to be conspecific. Many Japanese literatures have described phenotypic differences between these two morphs; P. japonicus possessing larger eye (eye diameter/snout length larger than 2/3) and pale brown body is distributed deep seafloor (150‒650m) in south of Tokyo Bay, while P. maximowiczi possessing smaller eye (eye diameter/snout length less than 2/3) and dark brown body is distributed shallow seafloor (≤ several tens of meters) in south of Hokkaido. We collected 44 Physiculus individuals (13 from shallow area and 31 from deep area) from northern to central Japan and performed nucleotide sequence analysis on the mitochondrial COI, 16S rRNA and Dloop regions. Body color largely varied, but dark brown individuals were abundant in the shallow group and pale brown individuals were abundant in the deep group. Ratio of eye diameter to snout length also largely varied, but the average was larger in the deep group than in the shallow group. In contrast, genetic difference among individuals and between shallow and deep groups was very small, and phylogenetic analysis indicated all individuals analyzed to be conspecific. These indicate that P. maximowiczi is a junior synonym of P. japonicus and phenotypic differences are intraspecific variation probably in response to the environmental diversity.
