Bivaginogyrus exiguus, 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 : 87-89

Bivaginogyrus exiguus n. sp.

[New Japanese name: Hime-futa-ana-mushi] ( Figs 9 , 10 )

Type material. Holotype ( MPM Coll.-No. 21942: PG) from the Senō River . Paratypes 32 specimens: three specimens from the Bafumi River ( MPM Coll.-No. 21943: PG); seven specimens from the Kashiranashi River ( MPM Coll.- No. 21929: HH); three and 11 specimens from the Senō River ( MPM Coll.-No. 21903: HH, MPM Coll.-No. 21926: one HH and 10 PG), respectively; one specimen from Sunaoshi River ( MPM Coll.-No. 21944: PG); three specimens from an irrigation canal of the Kiso River ( MPM Coll.-No. 21934: PG); one specimen from an irrigation canal of Lake Biwa ( MPM Coll.-No. 21945: PG); two specimens from an irrigation canal of the Mibara River ( MPM Coll.-No. 21946: PG); and one specimen from an irrigation canal of the Midori River ( MPM Coll.-No. 21932: HH) .

Other specimens deposited. Non-type specimens: nine specimens from the Kashiranashi River ( MPM Coll.-No. 21916: PG); three specimens from an irrigation canal of the Nomoto River ( MPM Coll.-No. 21936: PG); four specimens from an irrigation canal of the Sugata River ( MPM Coll.- No. Coll. -No.21947: PG); 12 specimens from an irrigation canal of the Kuzuryū River ( MPM Coll.-No. 21949); seven specimens from the Chōmeiji River ( MPM Coll.-No. 21939: PG); five specimens from the Ama River ( MPM Coll.-No. 21941: PG); seven specimens from an irrigation canal of the Ashida River ( MPM Coll.-No. 21923: four HH and three AC); two specimens from an irrigation canal of the Masugata River ( MPM Coll.-No. 21910: PG); and two specimens from an irrigation canal of the Mogami River ( MPM Coll.-No. 21913: PG) .

Description. Body ( Fig. 9 ) elongate, length including haptor 148–442 (263, n = 30), width at mid-body 31–81 (59, n = 30). Three pairs of head organs. Two pairs of eye-spots with some accessory eyes. Pharynx rounded, length 9–29 (16, n = 29), width 8–20 (14, n = 29); esophagus present; bifurcate intestine with branches confluent posterior to germarium.

Haptor length 40–89 (60, n = 20), width 57–142 (91, n = 20). Dorsal hamulus ( Fig. 10 ), total length 29–39 (33, n = 22), length to notch 25–31 (29, n = 22), outer root length, 1–4 (2, n = 22), inner root length 2–7 (5, n = 22), point length 10–12 (11, n = 22). Dorsal bar ( Fig. 10 ) broadly M-shaped, total length 1–5 (3, n = 22), median length 1–3 (2, n = 22), total width 16–20 (18, n = 22). Ventral bar ( Fig. 10 ) broadly V-shaped, total length 1–5 (3, n = 12), median length 1 (1, n = 12), total width 13–20 (16, n = 12). Marginal hooks ( Fig. 10 ) in 7 pairs; hook length: pair I shortest, 14–17 (15, n = 21); pair II 19–22 (21, n = 20); pair III 24–27 (26, n = 21); pair IV 24–28 (26, n = 21); pair V 17–20 (19, n = 21); pair VI 19–25 (22, n = 20); pair VII 17–21 (19, n = 19). Pair of needles ( Fig. 10 ), length 6–8 (7, n = 18) located near tips of marginal hook pair V.

Testis ( Fig. 9 ) elongate, dorsal to germarium, length 18–71 (n = 10), width 12–27 (n = 10). Vas deferens arising from anterior part of testis, looping dorsoventrally around left intestine, dilating seminal vesicle before entering into base of penis. Two prostatic reservoirs: one pyriform; the other fusiform, connecting prostatic gland ranged dorsal region of anterior trunk. Male copulatory organ ( Fig. 10 ) length 15–21 (18, n = 22), consisting penis and accessory piece. Penis slightly curved tube, length 16–20 (18, n = 22). Sclerotized accessory piece ( Fig. 10 ), length 11–16 (13, n = 22), rod-shaped with extended tip holding tip of penis.

Germarium ( Fig. 9 ) elongate, in mid-body, length 23–47 (n = 10), width 15–32 (n = 10). Oviduct arising from anterior part of germarium, continuing as oötype. Seminal receptacle inverted triangle, dorsal to oötype, connecting lower part of oötype. Mehlis’ gland connecting oötype. Two vaginae arising from each upper apexes of seminal receptacle, looping intestines ventrodorsally, consisting sclerotized tube [ Fig. 10 , length 7–10 (8, n = 10)], opening individually at mid-length on dorsal body surface. Vitellarium approximately co-extensive with intestine.

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

Other host. Gnathopogon caerulescens ( Cypriniformes : Gobionidae ).

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

Other localities. The Bafumi River (39°51′11″N, 140°03′58″E), Kana-ashi-iwase, Akita City, Akita Prefecture; 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; an irrigation canal of the Nomoto River (36°35′20″N, 140°01′28″E), Kami-takane-zawa, Takane-zawa-machi, Shioya County, Tochigi Prefecture; an irrigation canal of the Sugata River (36°25′46″N, 139°50′43″E), Nakadairyō , Shimotsuke City , Tochigi Prefecture; an irrigation canal of the Saruhashi River , Yamazaki-machi , Mitsuke City , Niigata Prefecture; an irrigation canal of the Kuzuryū River (36°10′01″N, 136°12′15″E), Kami-hyōgo , Sakai-chō , Sakai City , Fukui Prefecture; an irrigation canal of Lake Biwa (35°26′56″N, 136°11′55″E), Tsunosato , Kohoku-chō , Nagahama City , Shiga Prefecture; an irrigation canal of the Kiso River (35°17′32″N, 136°42′35″E), Shimo-naka-chō, Hashima City , Gifu Prefecture; the Chōmeiji River (35°09′55″N, 136°04′55″E), Kitatsuda-chō , Ōmi-hachiman City , Shiga Prefecture; the Ama River (34°51′23″N, 134°46′35″E), Yaebata , Shikitō-chō , Himeji City , Hyōgo Prefecture; the Mibara River (34°45′26″N, 132°54′43″E), Ōda-kō-machi, Miyoshi 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 .

Site of infection. Gill filaments.

Molecular sequence data. DDBJ accession numbers LC731711, LC731712, and LC731713 (28S rDNA) obtained from specimens collected from G. e. elongatus in Miyagi and Yamagata ( MPM Coll. - No. 21913) prefectures and from G . caerulescens in Shiga Prefecture ( MPM Coll.-No. 21939), respectively; LC731721 (18S-ITS1- 5.8S) obtained from specimens collected from G . e. elongatus in Yamagata Prefecture ( MPM Coll. - No. 21910) .

Etymology. This new species is smaller than B. japonicus n. sp. and B. cingulatus n. sp. and is named “ exiguus ” (little in Latin). The new Japanese name refers to the small size of this species: “hime” means small in Japanese.

Remarks. Bivaginogyrus exiguus n. sp. is distinguished from the other Bivaginogyrus species by the rod-shaped accessory piece with the extended tip and the vaginal pore with the sclerotized elongated tube. The new species is comparable to D. pandus Wu and Wang, 1983 and D. colpodes Wu, Wang, and Song, 1983 , both collected from G. imberbis , with respect to the shape of the male copulatory organ (anatomical details unknown: Wu and Wang 1983; Wu et al. 1983). However, the ventral bar of the new species is broadly V-shaped, which contrasts with the T-shaped ventral bar in D. pandus (Wu and Wang 1983) . The new species is also distinguished from D. colpodes whose penis with a semicircular bend toward the tip (Wu et al. 1983). In addition, B. exiguus n. sp. has a shorter penis (16–20 µm) than D. pandus [22– 28 µm (Wu and Wang 1983)] and D. colpodes [38–42 µm (Wu et al. 1983)].

Phylogenetic analysis

The topologies of the trees constructed using ML and BI analysis were almost identical ( Figs 11–13 ). The BI tree constructed based on 28S rDNA sequences is shown in Fig. 11 . Dactylogyrus labei Musselius and Gussev, 1976 diverges first, followed by four clades. Among these five clades, the initially branching Clade I consists of Dactylogyrus species parasitic on fishes in the family Cyprinidae , mainly from the Mediterranean coast. The tree is then divided into four major clades, Clades II and III, and IV and V, which form respective sister groups. Clade II comprises Bivaginogyrus and Dactylogyrus species, the hosts of which, with the exception of D. cryptomeres Bychowsky, 1934 , are fish in the families Xenocyprididae and Gobionidae from East Asia. The hosts of Dactylogyrus in Clade III are diverse, including fishes in the families Acheilognathidae , Lateolabracidae , Xenocyprididae , and Gobionidae , which are mainly distributed in Asia. Dactylogyrus tamoroko n. sp. is the only species in this clade infecting gobionid fish and shows affinities to D. pekinensis Gussev, 1962 and D. petruschewskyi Gussev, 1955 , the hosts of which are the Xenocyprididae in China. Clade IV comprises Dactylogyrus species isolated from fishes in the families Cyprinidae and Leuciscidae in Europe and America, whereas Clade V comprises Dactylogyrus species and Dactylogyroides tripathii (Yamaguti, 1963) from Far East Asia to Africa, where their main hosts are cyprinid fishes.

The BI tree constructed based on 18S-ITS1 sequences is shown in Fig. 12 . This tree is also divided into four major clades, Clades A to D. Clade A, the first to diverge, comprises Dactylogyrus and Bivaginogyrus species infecting fishes in the family Gobionidae . Within this clade, Bivaginogyrus is presented as a polyphyletic group. The next branch, Clade B, consists of Dactylogyrus species parasitizing Cyprinus carpio Linnaeus, 1758 and Carassius auratus (Linnaeus, 1758) . Clade C comprises the species parasitic on freshwater perch, Gymnocephalus cernua (Linnaeus, 1758) , from Europe and also on fishes in the Tincidae from China. Clade D consists of parasites of fishes in the Cyprinidae and Leuciscidae from China, Europe, and the United States, and with the exception of D. hemiamphibothrium Ergens, 1956 , Clade D includes the species clustered in Clade IV of the phylogeny based on the above 28S analysis.

The BI inferred based on 18S-ITS1-28S sequences is shown in Fig. 13 , focusing on the species that are paraphyletic with Bivaginogyrus species in Clade II ( Fig. 11 ) and Clade A ( Fig. 12 ). Bivaginogyrus becomes a paraphyletic group based on a sister group consisting of D. cryptomeres and D. squameus Gussev, 1955 .

Figures

Fig. 9. Whole body of Bivaginogyrus exiguus n. sp. (paratype, MPM Coll.-No. 21903, ventral view).

Fig. 10. Sclerotized parts of Bivaginogyrus exiguus n. sp. (holotype, MPM Coll.-No. MPM 21942). Male copulatory organ, ventral view.

Fig. 11. Bayesian inference (BI) tree based on partial 28S rDNA data (661bp including gaps) using Gobioecetes species as the outgroup. Accession numbers and scientific names of the newly sequenced species in this study are indicated in bold. The corresponding ISND accession numbers are shown. The tree includes results for BI and Maximum Likelihood with PP/BS branch support.

Fig. 12. Bayesian inference (BI) tree based on 18S-ITS1 data (720 bp including gaps) using Gobioecetes species as the outgroup. Accession numbers and scientific names of the newly sequenced species in this study are indicated in bold. The corresponding ISND accession numbers are shown. The tree includes results for BI and Maximum Likelihood with PP/BS branch support.

Fig. 13. Bayesian inference (BI) tree based on 18S-ITS1-28S data (1561bp including gaps) using Gobioecetes species as the outgroup. Scientific names of the newly sequenced species in this study are indicated in bold. The tree includes results for BI and Maximum Likelihood with PP/BS branch support.