Dactylogyrus oryziasi, Nitta & Nagasawa, 2017

Nitta, Masato & Nagasawa, Kazuya, 2017, Dactylogyrus oryziasi n. sp. (Monogenea: Dactylogyridae) from Oryzias latipes (Beloniformes: Adrianichthyidae) in Japan, Species Diversity 22 (1), pp. 1-5 : 2-4

Dactylogyrus oryziasi n. sp.

[New Japanese name: medaka-yubigata-mushi] ( Fig. 2 )

Holotype. NSMT-Pl 6291 fixed in APG.

Paratypes. Three specimens stained in Heidenhain’s iron hematoxylin (NSMT-Pl 6292) and six specimens fixed in APG (NSMT-Pl 6293).

Description. Body ( Fig. 2A ) including haptor length 459±99.0 (290–628; n =9), width at mid-body 95±12.9 (75–113; n =9). Three pairs of head organs. Two pairs of eye-spots with some dissociated eyes. Alimentary systems consisting of spherical pharynx: diameter 44±5.3 (33–50; n =9), esophagus and bifurcated intestine confluent just posterior to testis. Testis ovate to pyriform, postero-dorsal to ovary. Vas deferens arising from anterior part of testis, looping around left intestinal caeca onto ventral, extending seminal vesicle located dorsal to copulatory organ ( Fig. 2N ), entering base of copulatory organ. Two prostatic reservoirs saccate ( Fig. 2N ). Male copulatory organ ( Fig. 2M, N ) consisting of penis and accessory piece. Penis length 185±24.0 (155–226; n =7), clockwise coiling two and half and counterclockwise coiling one and half toward point; its tip passing through tube of accessory piece; its base touching base of sigmoid rod. Sclerotized accessory piece, length 23±1.6 (21–26; n =10), consisting of bended funnel-shaped tube and sigmoid rod connected to middle of tube. Ovary in mid-body, elongate. Oviduct arising anterior part of ovary, continuing as oötype surrounded by Mehlis’ gland. Vagina ( Fig. 2O ) thin sclerotized tube, length 75±15.3 (56–94; n =5), arising from right side of oviduct; vaginal pore located at mid-body on right ventral body surface. Vitellaria co-extensive with intestinal caeca.

Haptor length 48±7.2 (34–55; n =8), width 90±5.2 (85–98; n =8). Haptoral glands developed at base of haptor. Anchor ( Fig. 2B ) total length 23±0.9 (22–25; n =10), length to notch 19±0.7 (18–20; n =10), outer root length 3±0.5 (2–3; n =10), inner root length 8±0.9 (7–10; n =10), point length 7±0.7 (6–8; n =10). Dorsal bar ( Fig. 2C ) broad U-shape, total length 25±0.8 (24–26; n =10), total width 9±0.8 (8–10; n =10), median width 3±0.7 (2–4; n =10). Ventral bar ( Fig. 2D ) broad V-shape, total length 26±2.1 (24–31; n =10), total width 5±0.4 (4–5; n =10), median width 3±0.5 (2–3; n =10). Marginal hooks in 7 pairs; hook length: pair I ( Fig. 2E ) 16±0.5 (16–17; n =9); pair II ( Fig. 2F ) 16±0.4 (16–17; n =9); pair III ( Fig. 2G ) 17±0.7 (16–18; n =8); pair IV ( Fig. 2H ) 17±0.7 (16–18; n =9); pair V ( Fig. 2I ) 17±0.4 (16–17; n =9), pair VI ( Fig. 2J ) 17±0.5 (16–17; n =9); pair VII ( Fig. 2K ) 17±0.5 (16–17; n =9). Pair of needles ( Fig. 2L ), length 8±0.7 (7–9; n =9), located near top of second hooks.

Host. Oryzias latipes ( Beloniformes : Adrianichthyidae ).

Site of infection. Gill filaments.

Prevalence and intensity range (mean). Seven (35%) of 20 fish examined were infected by 1–4 (mean: 1.6) worms.

Sequence data. The partial 28S rDNA (696 bp) sequence was submitted to DDBJ (accession no. LC190737 ). A BLAST search of the sequence did not have any identical hit. The closest hits for this sequence are Dactylogyrus inexpectatus Isjumova in Gussev, 1955 ( AJ969945 , 88% similarity with 93% coverage), D. petruschewskyi Gussev, 1955 ( AY548927 , 87% similarity with 83% coverage), D. extensus Mueller and Van Cleave, 1932 ( AY553629 , 84% similarity with 93% coverage), D. hemiamphibothrium Ergens, 1956 ( AJ969946 , 84% similarity with 97% coverage) and D. lamellatus Achmerow, 1952 ( AY307019 , 84% similarity with 93% coverage).

Remarks. This new species corresponds to the diagnostic characteristics of the genus Dactylogyrus Diesing, 1850 ( Beverley-Burton 1984; Gussev et al. 2010), and the BLAST searches support the generic position of the species. Dactylogyrus oryziasi n. sp. resembles Dactylogyrus rysavyi Ergens, 1970 in a coiled penis passing through a tube of an accessory piece associated with a sigmoid rod, and the shape of the anchor ( Ergens 1970). The new species, however, differs from D. rysavyi which has the penis making right-hand one and half turns and left-hand one and half turns toward the point and the rod of the accessory piece connecting to the end of its tube ( Ergens 1970; Gussev et al. 2010).

Etymology. The new specific name is delivered from the generic name of the type host.

Japanese name. The new Japanese name is a combination of “medaka” and “yubigata-mushi”, which are the Japanese name of Oryzias and Dactylogyrus (as “yubigatamushi-zoku”), respectively.

Figures

Fig. 2. Dactylogyrus oryziasi n. sp., paratype (NSMT-Pl 6292) for A, N, holotype (NSMT-Pl 6291) for B–M, O. A, whole mount (ventral view); B, anchor; C, dorsal bar; D, ventral bar; E, marginal hook pair I; F, marginal hook pair II; G, marginal hook pair III; H, marginal hook pair IV; I, marginal hook pair V; J, marginal hook pair VI; K, marginal hook pair VII; L, needle; M, male copulatory organ (dorsal view); N, male genital organs (ventral view); O, vagina (dorsal view). Scale bars: A, 50µm; B–O, 10µm. Abbreviations: an, anchor; ap, accessory piece; e, eye; h, haptor; hg, haptoral grand; ho, head organ; i, intestine; mg, Mehlis’ gland; mh, marginal hook; n, needle; o, oötype; od, oviduct; ov, ovary; p, penis; ph, pharynx; pr, prostatic reservoir; sv, seminal vesicle; t, testis; v, vagina; vd, vas deferens; vl, vitellaria; vo, vaginal opening.