Rhabdias kiri, Sata & Takeuchi & Nakano, 2020

Sata, Naoya, Takeuchi, Hirohiko & Nakano, Takafumi, 2020, Description of a New Species of Rhabdias (Nematoda: Rhabditida: Rhabdiasidae) from Ishigakijima Island, Okinawa, Japan, Species Diversity 25, pp. 171-175 : 173-174

Genus Rhabdias Stiles and Hassall, 1905 Rhabdias kiri sp. nov.

( Fig. 1 )

Diagnosis. The East-Asian Rhabdias , with short and slen- der body. Buccal capsule small, 8.5 (8.6±1.2, 7.3–11.9) wide and 6.9 (6.6±1.1, 5.3–8.8) deep. Cuticular inflation less prominent in anterior and middle part of body.

Material examined. Holotype: KUZ Z2959 , whole specimen, adult female, obtained from the lung of M. okinavensis ( KUHE 61751 ), collected from Tozato (24°28′25″N, 124°14′45″E), Ishigakijima island, Okinawa Prefecture, Japan on 7 August 2019 . Paratypes: KUZ Z2960 – Z2967 , eight whole specimens obtained from the lung of the holotype’s host and other M . okinavensis specimens ( KUHE 61750 , 61751 ), data as for holotype; KUZ Z2968 , one section of anterior end of a female and remaining body; KUZ Z2968 was obtained from the lung of the holotype’s host specimen .

Additional materials. KUZ Z2969 , three whole-body specimens, and two non-deposited specimens for the present molecular studies, obtained from the same specimen of the holotype’s host ( KUHE 61751 ); one non-deposited specimen for the present morphological and molecular studies obtained from KUHE 61750 ; and one non-deposited specimen for the present molecular studies, obtained from a M . okinavensis specimen ( KUHE 61752 ), collected from Ishigaki (24°22′24″N, 124°08′59″E), Ishigakijima island, on 9 August 2019 .

Type locality. Japan, Okinawa: Ishigakijima island, Tozato (24°28′25″N, 124°14′45″E) .

Type host. Microhyla okinavensis Stejneger, 1901 ( Amphibia: Microhylidae ); site of infection: lung. A total of 17 individuals were obtained from three specimens of M. okinavensis ; mean intensity, followed by ranges: 5.7, 1–14.

Description. General. Body short and slender with tapered extremities, body becoming wider at region of vulva or slightly behind vulva. Cephalic end with six lips, each lip with one minute papilla. Amphids situated on posterior surface of lateral lips. Oral opening almost round. Cuticular inflation slightly inflated in anterior and middle part of body, slightly more prominent in caudal region. Anterior end of cuticular inflation possessing two prominent annulations.

Body length 4.54 mm (5.18± 0.99 mm, 4.14–7.07 mm), and maximum width 142 (146±14.6, 124–165). Body length/maximum body width=32.0 (29.2–43.7). Body width at junction of esophagus and intestine 97 (96±11.4, 79–121), at vagina 142 (145±15.8, 117–165), and at anus 68 (76±8.8, 65–90). Head diameter, 26 (25±1.5, 24–29) (n =9). Vestibulum funnel-shaped, 6.3 (7.1±1.2, 5.5–9.5) long. Buccal capsule small, possessing thick wall, cup-like in lateral view, nearly half or almost completely surround- ed by anterior end of esophagus, 6.9 (6.6±1.1, 5.3–8.8) deep, 8.5 (8.6±1.2, 7.3–11.9) wide. Esophagus possessing a slight dilation at anterior region of nerve ring. Esophagus 352 (348±37.5, 302–430) long [7.8% (5.6–8.9) of body length] with width of 21 (24±3.0, 20–30) at anterior end, 28 (31±2.8, 28–36) at dilated muscular part, 29 (30±3.4, 23– 34) at nerve ring, 54 (57±2.6, 52–60) at bulbar part. Nerve ring and excretory pore 118 (123±10.8, 111–150) [2.6% (1.6–3.1%) of body length] and 191 (193±12.6, 167–207) [4.2% (2.7–4.9%) of body length], respectively, from cephalic end, and 112 (114±10.6, 100–137) [31.8% (26.3–36.7%) of esophagus length] and 187 (186±12.3, 160–199) [53.1% (45.8–63.6%) of esophagus length], respectively, from anterior end of esophagus. Intestine thick walled. Anterior end of intestine wider than bulbar part of esophagus. Rectum, short, thin walled. Vulva 2.80 mm (2.89± 0.47 mm, 2.10–3.62 mm) from cephalic end [61.7% (49.9–61.7%) of body length], having slightly salient lips. Genital system amphidelphic, anterior limb turned posteriorly at 0.74 mm (1.15± 0.26 mm, 0.74–1.60 mm) from cephalic end, and posterior limb turned anteriorly at 0.54 mm (0.77± 0.29 mm, 0.52–1.40 mm) from tail end. Uteri long, tubular, filled with eggs, less than 100 (n =9). Tail long conical, sharply pointed, abruptly tapering from anus posteriorly, gradually tapering from mid-region to tip, 197 (208±32.4, 157–265) long [4.3% (3.1–4.9%) of body length]. Lateral pores observed in most specimens. Phasmids lateroventral, 145 (85–228) from tail end (n =6). Eggs elliptical, 80±5.68 (68–91) by 39±4.47 (30–50) (n =52), thin shelled, most eggs containing first stage larva.

Etymology. The specific name kiri is from a Japanese word kiri (=drill), which refers to the long and pointed tail of the new species, and thus treated as indeclinable.

DNA sequences. In total, 4 sequences were determined: one specimen obtained from the same host frog ( KUHE 61751 ) of the holotype, 2 sequences—COI ( LC547915 ; 655 bp), and 12S ( LC547917 ; 475 bp); one specimen obtained from a M . okinavensis specimen ( KUHE 61752 ) from Ishigaki , Ishigakijima island, 2 sequences—COI ( LC547916 ; 655 bp), and 12S ( LC547918 ; 475 bp) . Intraspecific variations were not observed in the 12S sequences; single nucleotide variation was detected in the COI sequences.

Remarks. Rhabdias kiri sp. nov. can be discriminated from the other 11 congeners recorded from East Asia and the Russian Far East as follows. The new species, of which body length ranges from 4.14 to 7.07 mm, can be distinguished from the following five Rhabdias species : R. bicornis Lu, 1934 (13.056 –15.428 mm; Lu 1934), R. incerta Wilkie, 1930 (14.3 mm; Wilkie 1930), R. kafunata Sata, Takeuchi, and Nakano, 2020 (10.99–16.77 mm; Sata et al. 2020), R. rhacophori Yamaguti, 1941 (10.55 mm; Yamaguti 1941) and R. tokyoensis Wilkie, 1930 (12 mm; Wilkie 1930). Rhabdias kiri sp. nov. can be differentiated from R. bermani Rausch, Rausch, and Atrashkevich, 1984 and R. polypedatis Yamaguti, 1941 by body shape because the latter two species possess much larger body widths relative to their body lengths than that of the new species [ R. bermani : 6.06–10.68mm long by 294–458 wide ( Rausch et al. 1984); and R. polypedatis : 4.2–5.2 mm long by 200–300 wide ( Yamaguti 1941)]. The new species is also distinguishable from R. montana Yamaguti, 1954 and R. nipponica Yamaguti, 1935 by the smaller width and depth of the buccal capsule, respectively [ R. montana : 15–16 wide ( Yamaguti 1954); and R. nipponica : 9–12 deep ( Yamaguti 1935)]. Additionally, R. kiri sp. nov. differs from R. nipponica because the new species possesses a much smaller head diameter (see Yamaguti 1954), and differs from R. globocephala Kung and Wu, 1945 and R. japalurae Kuzmin, 2003 in the absence of a cuticular inflation at the anterior and middle parts of the body ( Kung and Wu 1945; Kuzmin 2003, 2005).

The discovery of Rhabdias kiri sp. nov. from Ishigakijima island is the first record of the frog-parasitizing Rhabdias species from the Yaeyama Islands. A recent phylogeographic study of M. okinavensis , the only known host of Rhabdias kiri sp. nov., suggested that the Yaeyama Islands’ population of this frog is phylogenetically closer to a population of the continental species, M. mixture Liu and Hu, 1966 , than to the population of M. okinavensis from the central Ryukyus ( Tominaga et al. 2019). Thus, comprehensive taxonomic and phylogenetic studies of Rhabdias nematodes parasitizing Microhyla frogs in the East Asia would provide a new insight into the evolutionary history of parasites in the amphibians and reptiles of this area.

Figures

Fig. 1. Rhabdias kiri sp. nov., holotype (KUZ Z2959: A, C–E, G, H), paratypes (KUZ Z2968: B; KUZ Z2961: F). A, anterior region, lateral view; B, cephalic region, apical view; C, cephalic region, lateral view; D, vulvar region, lateral view; E, caudal region, lateral view; F, cuticular inflation in anterior region, lateral view; G, cuticular inflation in middle region, lateral view; H, cuticular inflation in caudal region, lateral view.