Dactylogyrus inversus Goto and Kikuchi, 1917

Nitta, Masato & Nagasawa, Kazuya, 2014, Three Species of Dactylogyrus (Monogenea: Dactylogyridae) Parasitic on Japanese Seabass Lateolabrax japonicus (Perciformes: Lateolabracidae) in Japan, with New Country Records for Dactylogyrus gotoi and Dactylogyrus kikuchii, Species Diversity 19, pp. 71-79 : 72-74

Dactylogyrus inversus Goto and Kikuchi, 1917 ( Fig. 2 )

Dactylogyrus inversus Goto and Kikuchi, 1917: 1–13 , figs 1–10; Ishii and Sawada 1938a: 231–232; Ishii and Sawada 1938b: 239; Yamaguti 1938: 16; Gussev 1967: 251; Chen 1984: 54; Gussev 1985: 188–189, fig. 282; Wu and Wang 1991: 73–74, fig. 49; Gibson et al. 1996: 17; Zhang et al. 2001: 76–77, fig. 9–2; 2003: 114; Ding and Liao 2004: 628–632; Šimková et al. 2006: 44; Gerasev et al. 2008: 323.

Dactylogyrus inversum [sic]: Ji et al. 1982: 13.

Microncotrematoides inversum: Yamaguti 1963: 33 , fig. 69.

Microncotrematoides inversus: Zhang et al. 1992: 131 ; Xia et al. 1999: 60; Wu 2000b: 424–425, fig. 377.

Microncotrema lateolabracis Yamaguti, 1958: 62–64 , fig. 11.

Dactylogyrus lateolabracis: Chen 1984: 54 ; Gibson et al.

1996: 19; Xia et al. 1999: 60.

Material examined. Seven of the 15 specimens deposit- ed (NSMT-Pl 6120) and three specimens deposited (togeth- er with two specimens of D. gotoi ) (NSMT-Pl 6122), Lake Nakaumi , Shimane Prefecture, Japan, 26 July 2012; eight of the 22 specimens deposited (NSMT-Pl 6121), Lake Shinji, Shimane Prefecture, Japan, 9 January 2013 .

Description. Body length including haptor 1595±545.0 (927–2773; n =16), width at mid-body 452±128.1 (235– 683; n =16). Internal anatomy shown in Fig. 2 A, I . Three pairs of head organs. Two pairs of eye-spots. Alimentary system consisting of subspherical pharynx (length 117±26.5 [83–176; n =16]; width 96±23.8 [61–152; n =16]), short oesophagus, and bifurcate intestine with branches confluent just anterior to haptoral glands. Testis ovoid, postovarian. Vas deferens arising from anterior region of testis, looping around left intestinal caeca towards ventral side of body. Small seminal vesicle represented by distended part of vas deferens before latter enters base of copulatory organ ( Fig. 2I ). Two prostatic reservoirs both saccate. Copulatory organ a slender tube, length 95±4.8 (88–104; n =16); sclerotized accessory piece shaped as twisted rod, length 87±3.6 (80– 93; n =16) ( Fig. 2H, I ). Ovary in mid-body. Vaginal armament unsclerotized; vaginal pore located at midlength on left dorsal body surface, vaginal duct arising from right side of seminal receptacle. Oviduct arising from anterior side of ovary. Uterus extending anteriorly to uterine pore, latter located close to copulatory organ. Mehlis’ gland near seminal receptacle. Vitelline system approximately co-extensive with intestinal caeca. Haptor length 128±30.5 (88–182; n =16), width 254±70.0 (172–421; n =16). Single pair of anchors ( Fig. 2B ), total length 27±0.9 (26–29; n =14), length to notch 18±0.6 (17–19; n =12), outer root length 3±0.5 (3–4; n =11), inner root length 13±1.0 (12–15; n =11), point length 13±1.4 (11–16; n =12). Each anchor with two filaments. Dorsal bar ( Fig. 2C ) total length 25±1.0 (23–26; n =15), total width 8±1.1 (6–9; n =14), median width 4±0.8 (3–6; n =15). Ventral bar absent. Hooks in 7 pairs ( Fig. 2A ); hook length: pair I ( Fig. 2D ) 40±6.5 (32–53; n =14); pair II 40±6.5 (32–53; n =14); pair III ( Fig. 2E ) 37±5.2 (30–48; n =14); pair IV 37±5.9 (27–49; n =14); pair V 39±6.0 (28– 49; n =14), pair VI 39±5.6 (30–49; n =14); pair VII ( Fig. 2F ) 37±5.2 (28–46; n =14). Pair of needles ( Fig. 2G ), length 10±0.8 (9–11; n =6), located near tips of second hook.

Host. Japanese seabass Lateolabrax japonicus ( Perciformes : Lateolabracidae ).

Site of infection. Gills.

Prevalence and intensity range (mean). 80% (8/10) and 1–8 (2.2) in Lake Shinji; no data for Lake Nakaumi.

Remarks. The present species was originally described by Goto and Kikuchi (1917) from the gills of L. japonicus from Japan. It was also reported by Yamaguti (1938) from L. japonicus in the Seto Inland Sea, Japan. Yamaguti (1963) transferred the species to a newly erected genus Microncotrematoides . Yamaguti (1958) had also described Microncotrema lateolabracis from the gills of L. japonicus in the Seto Inland Sea, but Gussev (1967) relegated this monogenean to the synonymy of D. inversus and also did not recognize the genus Microncotrematoides as valid. Chen (1984) transferred Microncotrema lateolabracis to Dactylogyrus as D. lateolabracis , which, however, has been regarded as a synonym of D. inversus ( Gibson et al. 1996) . The species has so far been reported from Japan ( Yamaguti 1938, 1958, 1963), China ( Gussev 1967; Ji et al. 1982; Chen 1984; Wu and Wang 1991; Zhang et al. 1992, 2001, 2003; Gibson et al. 1996; Xia et al. 1999; Wu 2000b; Ding and Liao 2004; Šimková et al. 2006) and the Russian Far East ( Gussev 1985; Gerasev et al. 2008). The specimens examined in this study conform to the descriptions and illustrations of D. inversus provided by Goto and Kikuchi (1917) from Japan and by Wu (2000b) from China. This species has also been reported from the chub mackerel Scomber japonicu s Houttuyn, 1782 ( Perciformes : Scombridae ) in Japan ( Ishii and Sawada 1938a). However, despite later examination of S. japonicu s for parasites in Japanese water ( Ichihara et al. 1968), there has been no rediscovery of D. inversus on this host. It is possible that Ishii and Sawada (1938a) misidentified or otherwise confused the hosts.

Figures

Fig. 2. Dactylogyrus inversus Goto and Kikuchi, 1917, NSMT-Pl 6121. A, whole mount (ventral view); B, dorsal anchors; C, dorsal bar; D, hook of pair I; E, hook of pair III; F, hook of pair VII; G, needle; H, male copulatory organ; I, male genital organs (ventral view). Scale bars: A, 500µm; B–G, 10µm; H, I, 20µm. Abbreviations: an, anchor; ap, accessory piece; co, copulatory organ; es; eye-spots; hg, haptoral glands; hk, hook; ho, head organ; in, intestine; mg, Mehlis’ gland; od, oviduct; oe, oesophagus; ov, ovary; ph, pharynx; pr, prostatic reservoir; sv, seminal vesicle; te, testis; ut, uterus; va, vaginal duct; vd, vas deferens; vp, vaginal pore; vs, vitelline system.