The worm eel, Muraenichthys okamurai Machida and Ohta 1996, a junior synonym of Muraenichthys borealis Machida and Shiogaki 1990

The worm eels, Muraenichthys okamurai Machida and Ohta 1996 and M. borealis Machida and Shiogaki 1990 , both from Japanese waters, have been distinguished by the difference in dentition on the upper jaw and palatal area, and regarded as valid species of Scolecenchelys . A detailed examination of the dentition of the type specimens and recently caught specimens revealed that the difference in the dentition described in the original descriptions is actually intraspecific variation. Apparently M. okamurai represents the juvenile of M. borealis , and the former is its junior subjective synonym.