Salsuginus seculus ( Mizelle and Arcadi, 1945 )

Nitta, Masato & Nagasawa, Kazuya, 2014, Salsuginus seculus (Monogenea: Ancyrocephalidae) Newly Recorded from Japan, Infecting the Introduced Mosquitofish Gambusia affinis, Species Diversity 19, pp. 173-178 : 174-176

Salsuginus seculus ( Mizelle and Arcadi, 1945) ( Fig. 1 )

Urocleidus seculus Mizelle and Arcadi, 1945: 293–296 , figs 1–20; Sproston 1946: 249, 525; Seamster 1948: 168; Mizelle et al. 1956: 174, 177; Yamaguti 1963: 83; Hoffman 1967: 93, 387; Nowlin et al. 1967: 111; Price 1968: 191; Meade and Bedinger 1972: 285, fig. 32.

Salsuginus seculus: Murith and Beverley-Burton, 1985: 705 , 712; Beverly-Burton and Klassen 1990: 5; Font 1997: 58; Hoffman 1999: 119; Aguilar-Aguilar et al. 2003: 1871; Aguilar-Aguilar et al. 2005: 238; Pineda-López et al. 2005: 441, 445; Ray 2005: 14; Salgado-Maldonado et al. 2005: 153, 156; Kohn et al. 2006: 35, 74; Salgado-Maldonado 2006: 165, 348; Salgado-Maldonado 2008; 39; Lee and Reusser 2012: 430–431; Zhang 2012: 103; Salgado-Maldonado and Quiroz-Martínez 2013: 5, 10, 12.

Material examined. Three specimens (NSMT-Pl 6127) from an irrigation canal flowing into Urauchi Bay , Okinawa Prefecture; 15 specimens (NSMT-Pl 6128) from an irrigation canal connected to the Ushitsu River , Saga Prefecture; 18 specimens (NMST-Pl 6129) from the middle reaches of the Umeda River , Aichi Prefecture; four specimens (NMST- Pl 6130) from an irrigation canal connected to the Yoshino River system, Tokushima Prefecture; three specimens (NMST-Pl 6141) from the Dōno River, Kyōto Prefecture, Japan .

Description. Body elongate in live, but greatly contract- ed upon fixation ( Fig. 1A ), 203±62.1 (129–354; n =36) long, 128±25.0 (71–178; n =35) wide. Three pairs of head organs. Usually one pair of eye-spots with some dissociated eyes, anterior pair present in some specimens. Alimentary system consists of spherical pharynx (diameter 21±4.1 [17–33; n =39]), esophagus very short or not present, and bifurcate intestinal caeca unit posterior to testis. Testis posterior to ovary. Vas deferens loops dorsoventrally around left intestinal caecum, seminal vesicle expanded before entering base of penis. Two glandular prostatic reservoirs arranged behind of penis; dorsal one rounded, ventral one U-shaped. Sclerotized penis ( Fig. 1G ) slightly curved, 19±1.0 (18–21; n =23) in chord length from base to tip; 29±1.8 (27–32; n =23) in arc length along curve. Accessory piece ( Fig. 1G ) rod-like with distal projection, length 14±1.0 (12–16; n =22). Ovary elliptical, with oviduct arising from its anterior part. Vaginal armament unsclerotized, surrounded by thick membrane. Vaginal pore located at same level as penis on left body surface, vaginal duct arising from left side of oötype. Oviduct originates from anterior side of ovary, continues as oötype. Uterus extending anteriorly to uterine pore close to penis. Mehlis’ gland connected to oötype. Vitellaria well developed, abundantly distributed around intestinal caeca.

Haptor length 35±7.9 (22–56; n =36), width 66±12.4 (46–103; n =36). Dorsal hamuli ( Fig. 1B ): total length 17±0.6 (16–18; n =13), length to notch 15±0.5 (15–16; n =13), deep root length 2±0.5 (1–2; n =13), superficial root length 7±0.9 (6–9; n =13), blade length 6±0.5 (5–6; n =13), curvature of blade 0.8±0.04 (0.7–0.8; n =13). Ventral hamuli ( Fig. 1C ): total length 19±1.0 (17–21; n =17), length to notch 17±1.0 (16–19; n =17), deep root length 2±0.5 (1–2; n =17), superficial root length 9±1.0 (7–10; n =17), blade length 6±0.4 (5–7; n =17), curvature of blade 0.9±0.1 (0.7– 0.9; n =17). Dorsal bar ( Fig. 1D ): transverse length 23±1.6 (20–27; n =41), median width 3±0.6 (2–4; n =41); distal notch blunt or absent in some specimens. Ventral bar ( Fig. 1E ): transverse length 25±1.9 (21–29; n =39), median width 3±0.6 (2–4; n =39); distal notch sharp. Larval hooks in 7 pairs ( Fig. 1F ), all similar in shape and size; length 10±0.5 (10–11; n =42).

Host. Mosquitofish Gambusia affinis ( Cyprinodontiformes : Poeciliidae ).

Site of infection. Gills.

Remarks. The present collection represents the first records of S. seculus from Japan. The species was originally described as Urocleidus seculus from Gambusia affinis (as G. affinis affinis ) collected in California, USA ( Mizelle and Arcadi, 1945), and was later transferred to Salsuginus by Murith and Beverley-Burton (1985). The species has been reported from Mexico ( Aguilar-Aguilar et al. 2003; Salgado- Maldonado et al. 2005) and Hawaii ( Font 1997), in addition to the continental United States (California: Mizelle and Arcadi (1945); Louisiana: Seamster (1948); Texas: Nowlin et al. (1967), Meade and Bedinger (1972)).

The measurements and morphology of sclerotized parts of the specimens of S. seculus collected in the present study are almost identical to those of representatives of this species from California and Texas ( Mizelle and Arcadi 1945; Meade and Bedinger 1972). The measurements of haptoral sclerotized parts of the specimens also agree with those of S. seculus reported by Rand and Wiles (1987), but the dorsal deep root and ventral blade of the present specimens (1–2 and 5–6 µm, respectively) are slightly shorter than those reported earlier (3 and 7 µm, respectively).

Twelve species of Salsuginus are currently recognized as valid (in alphabetical order): S. angularis (Mueller, 1934) ; S. bahamianus ( Hanek and Fernando, 1972) ; S. bermudae Rand and Wiles, 1987 ; S. cubensis Mendoza-Franco, Vidal-Martínez, Cruz-Quintana and León, 2006 ; S. fundulus ( Mizelle, 1940) ; S. heterocliti Murith and Beverley-Burton, 1985 ; S. neotropicalis Mendoza-Franco and Vidal-Martínez, 2001 ; S. seculus ( Mizelle and Arcadi, 1945) ; S. spirae ( Williams, 1980) ; S. thalkeni Janovy, Ruhnke and Wheeler, 1989 ; S. umbraensis ( Mizelle, 1938) ; and S. yutanensis Ferdig, McDowell and Janovy, 1991 . Salsuginus seculus differs from both S. umbraensis and S. fundulus which are characterized by the same size of the dorsal and ventral hamuli ( Mizelle 1938, 1940; Beverley-Burton 1984; Murith and Beverley- Burton 1985). By the accessory piece length, S. seculus (12– 16 µm: this study) is distinguished from S. bahamianus (27– 34 µm: Hanek and Fernando 1972), S. heterocliti (20–24 µm: Murith and Beverley-Burton 1985), and S. spirae (20–25 µm: Williams 1980; 19–20 µm: Murith and Beverley-Burton 1985). The accessory piece of S. seculus has one process, while those of S. angularis , S. bermudae , S. cubensis , and S. heterocliti possess multiple processes (Murith and Beverley- Burton 1985; Rand and Wiles 1987; Mendoza-Franco et al. 2006). Salsuginus seculus is also discerned from S. neotropicalis which has a ventral bar with enlarged globose ends ( Mendoza-Franco and Vidal-Martínez 2001). The dorsal curvature of the blade in S. seculus (0.8: this study) is small- er than that in S. thalkeni (1.0: Janovy et al. 1989) and S. yutanensis (1.1: Ferdig et al. 1991).

Salsuginus seculus is the third species of parasite reported from mosquitofish in Japan. To date, Genarchopsis goppo Ozaki, 1925 (Digenea: Derogenidae ) and Neoergasilus japonicus (Harada, 1930) (Copepoda: Ergasilidae ) have been recorded from the fish ( Shimazu et al. 2011, Nagasawa and Uyeno 2012). These parasite are native to Far East Asia ( Shimazu 1995, Nagasawa and Uyeno 2012) and are not introduced species of North American origin.

Figures

Fig. 1. Salsuginus seculus (Mizelle and Arcadi, 1945). NMST-Pl 6129 for A and NMST-Pl 6141 for B–G. A, whole mount (ventral view); B, dorsal hamulus; C, ventral hamulus; D, dorsal bar; E, ventral bar; F, larval hook; G, male copulatory organ; Scale bars: A, 50µm; B–G, 10µm. Abbreviations: ap, accessory piece; es, eye-spot; ho, head organ; in, intestinal caeca; mg, Mehlis’ gland; o, oötype; od, oviduct; ov, ovary; p, penis; ph, pharynx; pr, prostatic reservoir; sv, seminal vesicle; t, testis; v, vitellaria; va, vagina; vp, vaginal pore; vd, vas deferens.