Dactylogyrus squameus Gussev, 1955 [New Japanese name: Motsugo-yubigata-mushi] (Fig. 2) Dactylogyrus squameus Gussev, 1955: 207–209, fig. 10-3; Bykhovskaya-Pavlovskaya et al. 1962: 310, 312, fig. 619; Gvozdev and Agapova 1977: 109, 112; Ji et al. 1982: 21; Chen 1984: 53; Gussev 1985: 133, fig. 178; Wu and Wang 1991: 121, fig. 120; Gibson et al. 1996: 30; Liang 2000: 243–244, fig. 192; Ondračkova et al. 2004: 140, 143–144, fig. 5; Šimková et al. 2004: 1003, 1006, 1007, 1008, 1011; Šefrová and Laštůvka 2005: 157; Galli et al. 2007: 265, 267, 269, 270; Gerasev 2008: 407; Karabekova 2008: 331, 333; Gozlan et al. 2010: 330, 331; Gussev et al. 2010: 199, 201, fig. 229; Anonymous 2012: 51, 52; Davydov et al. 2012: 73, 74; Witkowski and Grabowska 2012: 81; Balbuena et al. 2013: 4; Ekmekçi et al. 2013: 116. Neodactylogyrus squameus: Yamaguti 1963: 43, fig. 703. Material examined. Ten specimens were used for the description: eight specimens fixed in APG (NSMT-Pl 6176, 6177); one specimen stained in Heidenhain’s iron hematoxylin (NSMT-Pl 6179 together with two specimens of B. obscurus); and one specimen (NSMT-Pl 6178) stained in alum carmine; from Ibaraki, Nara, and Tottori prefectures, respectively. Description. Body length including haptor 526±133.0 (241–683, n =9), width at mid-body 76±15.3 (57–102, n =9). Three pairs of head organs. Two pairs of eye-spots. Alimentary system consisting of subspherical pharynx, length 31±5.0 (20–37, n =9), width 28±5.1 (20–35, n =9), followed by esophagus and bifurcate intestine with branches confluent just anterior to tests. Testis pyriform, dorsal to ovary. Vas deferens arising from anterior region of testis, looping around left intestine towards ventral side of body, distended as seminal vesicle before entering base of copulatory organ. Two prostatic reservoirs both saccate. Copulatory organ (Fig. 2L) a curved tube, organ length 22±1.2 (20– 24, n =8), tube length 22±1.7 (19–24, n =8). Sclerotized accessory piece sigmoid, its root touching base of copulatory organ and holding copulatory organ by its process, accessory piece length 21±1.6 (19–24, n =8). Ovary in mid-body. Oviduct arising from anterior side of ovary, continuing as oötype surrounded by Mehlis’ gland and uterus. Vagina unsclerotized, running ventrally from right side of seminal receptacle located to right of oötype to vaginal opening on right body surface. Vitellaria approximately co-extensive with intestine. Haptor length 72±14.1 (43–94, n =9), width 106±30 (62– 138, n =9). Dorsal anchor (Fig. 2B) of total length 33±2.4 (28–35, n =10), length to notch 28±1.9 (25–30, n =10), outer root length 5±0.5 (4–5, n =10), inner root length 8±1.2 (7– 10, n =10), point length 10±0.7 (9–11, n =10). Dorsal bar (Fig. 2C) bow-shaped, of total length 22±1.4 (21–25, n =10), total width 8±0.7 (7–9, n =10), median width 5±0.6 (4–6, n =10). Ventral bar (Fig. 2D) thin, slightly curved, of total length 24±2.6 (21–28, n =7), total width 2±1.0 (1–4, n =7), median width 1.1±0.4 (1–2, n =7). Marginal hooks in 7 pairs; length: pair I (Fig. 2E) 17±1.0 (15–18, n =9); pair II (Fig. 2F) 19±1.1 (18–21, n =9); pair III (Fig. 2G) 22±1.0 (20–23, n =9); pair IV (Fig. 2H) 25±1.9 (22–27, n =9); pair V (Fig. 2I) 22±1.0 (21–24, n =9); pair VI (Fig. 2J) 21±1.0 (20–23, n =9); pair VII (Fig. 2K) 19±1.0 (17–20, n =9). Pair of needles (Fig. 2M) of length 9±0.9 (8–10, n =9), located near tips of second hooks. Host. Pseudorasbora parva (Cypriniformes: Cyprinidae). Site of infection. Gills. Prevalence and intensity range (mean). 100% (2/2) and 1–2 (1.5) in the Tomio River, Nara Prefecture; 25% (1/4) and 1 in the Kitakata River, Tottori Prefecture; 40% (4/10) and 1–3 in Lake Kasumigaura, Ibaraki Prefecture. Remarks. Dactylogyrus squameus was originally described by Gussev (1955) from the gills of Pseudorasbora parva from the Amur River and Lake Chanka, Far-East Russia, and subsequently reported from the same host in Heilongjiang, Liaoning, Hubei, and Yunnan, China (Ji et al. 1982; Chen 1984; Wu and Wang 1991; Liang 2000). The species was transferred to the genus Neodactylogyrus by Yamaguti (1963), although this genus had been synonymized with Dactylogyrus by Mizelle and Donahue (1944). The specimens examined in this study almost conform to the descriptions and illustrations of D. squameus by Gussev (1955, 1985), Bykhovskaya-Pavlovskaya et al. (1962), Wu and Wang (1991), Liang (2000), Ondračkova et al. (2004), and Gussev et al. (2010). The dorsal anchors of our specimens are slightly smaller than those authors’ measurements, but this may be due to intraspecific variation because the anchor’s shape and the male copulatory organs of our specimens agree with the cited descriptions. The present collection in Japan represents a new country record for Dactylogyrus squameus. This monogenean established populations infecting Pseudorasbora parva in Kazakhstan, Tajikistan, the Kyrgyz Republic, Ukraine, the Czech Republic, Slovak Republic, and Italy after both species were introduced from Far-East Asia into these countries (Gvozdev and Agapova 1977; Gussev 1985; Ondračkova et al. 2004; Galli et al. 2007). Ondračkova et al. (2004) listed the monogenean as occurring in “ Uzbekistan ” by reference to Gussev (1985), but this was most probably a mistranslation of “ Ukraine ”. Japanese name. The new Japanese name is a combination of “motsugo” and “yubigata-mushi”, which are the Japanese names of P. parva and the genus Dactylogyrus (as “yubigata-mushi-zoku”), respectively.

Published as part of Nitta, Masato & Nagasawa, Kazuya, 2016, New Geographical Records of Three Gill Monogeneans (Platyhelminthes) Parasitic on Pseudorasbora parva (Cypriniformes: Cyprinidae) in Japan, pp. 1-7 in Species Diversity 21 (1) on pages 2-5, DOI: 10.12782/sd.21.1.001, http://zenodo.org/record/4583528