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.