A single juvenile specimen (93.2 mm standard length) of the rare syngnathid fish Microphis (Coelonotus) argulus, collected from the Uchizuma-gawa River, Tokushima Prefecture, Shikoku Island, Japan, is the first record from Shikoku Island and northernmost record of the species. We newly found that M. (C.) argulus is distinguished from M. (C.) leiaspis in the fresh juvenile specimens by the following combination of characters: jaws to snout reddish (vs. brownish in the latter); small white dots present from behind eye to pectoral-fin base (vs. absent); operculum and pectoral-fin base brownish (vs. silverywhite). The M. (C.) argulus specimen may have been transported northward by the Kuroshio Current from the usual distribution range of the species, and recruited to the Uchizuma-gawa River.
