Bivaginogyrus japonicus, Nitta & Nagasawa, 2023

Nitta, Masato & Nagasawa, Kazuya, 2023, Gill Monogeneans (Platyhelminthes) Parasitic on Gnathopogon elongatus elongatus and G. caerulescens (Cypriniformes: Gobionidae) from Japan, with Descriptions of One New Species of Dactylogyrus and Three New Species of Bivaginogyrus (Dactylogyridae), Species Diversity 28 (1), pp. 69-97 : 82-84

publication ID	https://doi.org/ 10.12782/specdiv.28.69
publication LSID	lsid:zoobank.org:pub:9EBCA89B-8AF5-4EBF-8D0F-1916D9DFA6BB
persistent identifier	https://treatment.plazi.org/id/21C5C447-B3DC-4DE2-89D9-58D002268DE5
taxon LSID	lsid:zoobank.org:act:21C5C447-B3DC-4DE2-89D9-58D002268DE5
treatment provided by	Felipe
scientific name	Bivaginogyrus japonicus
status	sp. nov.

Treatment

Bivaginogyrus japonicus View in CoL n. sp.

[New Japanese name: Yamato-futa-ana-mushi] ( Figs 4–6 View Fig View Fig View Fig )

Type material. Holotype ( MPM Coll.-No. 21901: PG) from the Senō River . Paratypes 34 specimens: eight specimens from the Senō River ( MPM Coll.-No. 21902: one PG and seven HH); four specimens from the Sunaoshi River ( MPM Coll.-No. 21904: PG); one specimen from Harayachi River ( MPM Coll.-No. 21905: PG); six specimens from an irrigation canal of the Omoi River ( MPM Coll.-No. 21906: PG); two specimens from the Sugata River ( MPM Coll.-No. 21917: PG); two specimens from an irrigation canal of the Kiso River ( MPM Coll.-No. 21907: PG); and four specimens from an irrigation canal of the Midori River ( MPM Coll.- No. 21919: HH) .

Other specimens deposited. Non-type specimens: seven specimens from an irrigation canal of the Masugata River ( MPM Coll.-No. 21908: PG); five specimens from an irrigation canal of the Mogami River ( MPM Coll.-No. 21911: PG); two specimens from the Kashiranashi River ( MPM Coll.-No. 21914: PG); three specimens from an irrigation canal of the Sugata River ( MPM Coll.-No. 21920: PG); three specimens from the Tama River ( MPM Coll.-No. 21912: APG); and 35 specimens from an irrigation canal of the Ashida River ( MPM Coll.-No. 21922: six HH and 29 AC) .

Description. Body ( Fig. 4 View Fig ) elongate, length including haptor 279–1024 (624, n = 33), width at mid-body 65–244 (149, n = 33). Three pairs of head organs. Head gland cells on both sides of body at level of anterior part of pharynx. Two pairs of eye-spots with some accessory eyes. Pharynx ovate, length 31–89 (54, n = 32), width 28–71 (47, n = 32); esophagus followed by bifurcate intestine with branches confluent posterior to testis. Well-developed gland on short peduncle and haptor.

Haptor length 44–95 (66, n = 22), width 73–157 (119, n = 22). Dorsal hamulus ( Fig. 5 View Fig ), total length 22–25 (23, n = 22), length to notch 15–18 (17, n = 22), outer root length, 1–4 (2, n = 22), inner root length 9–12 (11, n = 22), point length 12–14 (13, n = 22). Dorsal bar ( Fig. 5 View Fig ) slightly bent at both ends, total length 4–5 (5, n = 21), median length 2–4 (3, n = 21), total width 20–27 (23, n = 21). Ventral bar absent. Marginal hook ( Fig. 5 View Fig ) in 7 pairs; hook length: pair I 22–27 (24, n = 19); pair II 19–24 (21, n = 19); pair III 21–27 (23, n = 19); pair IV 23–28 (25, n = 19); pair V 19–22 (20, n = 19); pair VI 20–25 (22, n = 19); pair VII 20–25 (22, n = 19). Pair of needles ( Fig. 5 View Fig ), length 8–12 (10, n = 19) located near tips of marginal hook pair V. Reservoirs associating with each marginal hooks ( Fig. 6C View Fig ).

Testis ( Fig. 4 View Fig ) ovate to pyriform, posterior to germarium, length 54–98 (70, n = 14), width 37–59 (48, n = 14). Vas deferens arising from anterior part of testis, looping around left intestine towards ventral side of body. Seminal vesicle expanded before entering into base of penis. Two prostatic reservoirs saccate: one saccate; the other elongate, connecting prostatic gland distributed dorsal inter-intestinal region of anterior trunk. Male copulatory organ length 29–38 (34, n = 22), consisting penis and accessory piece ( Fig. 5 View Fig ). Penis slightly curved tube, length 31–39 (35, n = 22). Sclerotized accessory piece bifurcated at mid-length and holding copulatory organ, length 27–37 (32, n = 22).

Germarium ( Fig. 4 View Fig ) ovate, in mid-body, length 32–116 (83, n = 14), width 25–67 (49, n = 14). Oviduct arising from anterior part of germarium, continuing as oötype. Seminal receptacle located ventral of oviduct, connecting base of oötype. Mehlis’ gland connecting lowest part of oötype. Two vaginae extending from each side of seminal receptacle, running ventrally to sclerotized vaginal pores [ Fig. 5 View Fig , length 7–11 (9, n = 17)] located individually on both sides of dorsal mid-body surface. Vitellarium approximately co-extensive with intestine.

Type host. Gnathopogon e. elongatus ( Cypriniformes : Gobionidae ).

Type locality. The Senō River (34°36′16″N, 133°51′52″E), Uchio, Minami District , Okayama City , Okayama Prefecture GoogleMaps .

Other localities. The Sunaoshi River (38°18′16″N, 140°58′43″E) and the Harayachi River (38°18′16″N, 140°58′42″E), Nangū-hachiman, Tagajō City, Miyagi Prefecture; an irrigation canal of the Masugata River (38°45′54″N, 140°16′31″E), Tōka-machi, Shinjō City, Yamagata Prefecture; an irrigation canal of the Mogami River (37°58′43″N, 140°09′20″E), Iryūda, Higashi-okitama Takahata-machi, Yamagata Prefecture; the Kashiranashi River (37°29′56″N, 138°55′13″E), Yamazaki-machi, Mitsuke City, Niigata Prefecture; an irrigation canal of the Omoi River (36°26′04″N, 139°46′43″E), Mibu-machi, Shimatsuga County, Tochigi Prefecture; an irrigation canal of the Sugata River (36°25′46″N, 139°50′43″E), Nakadairyō , Shimotsuke City , Tochigi Prefecture; the Tama River (35°36′32″N, 139°37′49″E), Tamagawa , Setagaya Ward , Tokyo; an irrigation canal of the Kiso River (35°17′32″N, 136°42′35″E), Shimo-naka-chō, Hashima City , Gifu Prefecture; an irrigation canal of the Ashida River (34°31′51″N, 133°22′04″E), Kawa-minami , Kan-nabe-chō, Fukuyama City , Hiroshima Prefecture; and an irrigation canal of the Midori River (32°45′15″N, 130°46′02″E), Shimo-rokka , Kashima-machi , Kami-mashiki County , Kumamoto Prefecture GoogleMaps .

Site of infection. Tip of the gill filament.

Molecular sequence data. DDBJ accession numbers LC731714 and LC731715 (28S rDNA) obtained from specimens collected from G. e. elongatus in Miyagi and Yamagata ( MPM Coll.-No. 21908) prefectures, respectively.

Etymology. The specific name is derived from the type locality, Japan. The new Japanese name, “yamato” means Japan, and “futa-ana-mushi” does the genus Bivaginogyrus .

Remarks. Bivaginogyrus japonicus n. sp. differs from the other Bivaginogyrus species by the forked accessory piece and the absence of the ventral bar. The new species is close to D. polylepidis Alvarez Pellitero, Simon Vicente, and Gonzalez Lanza, 1981 (anatomical details unknown) with respect to the absence of the ventral bar and the male copulatory organ consisting of a bifurcated accessory piece and a slightly curved penis ( Álvarez Pellitero et al. 1981). However, the marginal hook of pair XII of D. polylepidis is exceptionally well developed [about twice as long than the others ( Álvarez Pellitero et al. 1981)], but there is no such difference in the size of the marginal hooks of the new species. In addition, B. japonicus n. sp. differs from D. polylepidis in having the sclerotized vaginal pore and the smaller dorsal hamuli [22–25 µm vs. 43–51 µm ( Álvarez Pellitero et al. 1981)].

Although we were unable to clearly observe the connection between the gland in the peduncle and the reservoir associated with the marginal hook, they are assumed to be separate organs (see Wong et al. 2008).

The new species was found to aggregate at the tips of the gill filaments ( Fig. 6A View Fig ). Within the host tissues, filament-like structures, which are assumed to be derived from secretions of the reservoirs associated with each marginal hook (see Discussion), were connected to the cartilage tissue of the gill ( Fig. 6B View Fig ). In addition, the tips of parasitized gill filaments were observed to be swollen, owing to the proliferation of epithelial tissues ( Fig. 6A View Fig ).