Argulus species

Nagasawa, Kazuya, 2023, First Japanese Record of Argulus nobilis (Crustacea: Branchiura: Argulidae), an Ectoparasite of Gars of North American Origin, Species Diversity 28 (2), pp. 205-215 : 213

Key to the Japanese freshwater Argulus species

As stated in the above Remarks, six species of Argulus have been recorded from wild and captive freshwater fishes in Japan. Of these species, a branchiuran reported as A. foliaceus by Tsutsumi (1968, 1977) was clearly misidentified ( Shimura and Asai 1984) and needs re-examination, but these specimens could not be located by the present author, which indicates that they most probably have been lost. A key to the remaining five species of Argulus reported from freshwater fishes in Japan is given here, based on the present and previous papers ( Wilson 1912, 1924 for male A. nobilis ; Meehean 1940 for A. americanus ; Hoshina 1950; Shimura and Asai 1984; Nagasawa 2021; Nagasawa and Taniguchi 2021; Nagasawa et al. 2022a). Previously, four to “eight” plumose setae on the posterior margin of the coxa of the first leg were reported to be important for identification of A. coregoni ( Nagasawa and Taniguchi 2021; Nagasawa et al. 2022a), “eight” is herein changed to “nine” because the male and female of the species has four to eight and five to nine plumose setae, respectively ( Hoshina 1950: table 1). The key can be used for both sexes.

1. Frontal region of carapace protruding anteriorly.......2

—Frontal region of carapace not protruding anteriorly....4

2. Horizontal anterior margin of frontal region.................................. A. mongolianus Tokioka, 1936

—Rounded anterior margin of frontal region............3

3. Two or three sclerites per supporting rod of first maxilla......................... A. americanus Wilson, 1902

—Ten or more sclerites per supporting rod of first maxilla............................... A. nobilis Thiele, 1904

4. A single plumose seta present on posterior margin of coxa of first leg............... A. japonicus Thiele, 1900

— Four to nine plumose setae present on posterior margin of coxa of first leg............ A. coregoni Thorell, 1864