Rhadinorhynchus seriolae ( Yamaguti, 1963 )

Kita, Yuki, Nitta, Masato & Kajihara, Hiroshi, 2024, Morphological and Molecular Characteristics of Two Species of the Genus Rhadinorhynchus (Palaeacanthocephala: Echinorhynchida) from the Western Pacific, Species Diversity 29 (1), pp. 171-178 : 172-173

Rhadinorhynchus seriolae ( Yamaguti, 1963) ( Fig. 1 )

Rhadinorhynchus pristis (not of Rudolphi 1802): Fukui and Morisita 1937: 1844 (Momotori, Mie, Japan) .

Nipporhynchus seriolae Yamaguti, 1963: 104 (Momotori, Mie, Japan; a market in Tokyo, Japan).

Rhadinorhynchus seriolae : Golvan 1969: 81 (localities same as Yamaguti 1963); Smales 2014: 726, fig. 3 (Killarney, Victoria, Australia; Sir John Young Banks, New South Wales, Australia).

Material examined. Three specimens (on one slide), ICHUM 8571 , off Minami-Ise, 22 August 2022, from the intestine of Thunnus orientalis .

Type locality. Off Momotori ( Toshi Island , Mie, Japan) ( Yamaguti 1963) .

Other localities. Off Killarney (Victoria, Australia) ( Smales 2014); off Minami-Ise (Mie, Japan) (this study); off Sir John Young Banks (New South Wales, Australia) ( Smales 2014); Tokyo (market, collected site unknown) ( Yamaguti 1963).

Type host. Seriola quinqueradiata Temminck and Schlegel, 1845 ( Carangidae ) ( Yamaguti 1963).

Other hosts. Scomber japonicus Houttuyn, 1782 ( Scombridae ) ( Yamaguti 1963); Seriola lalandi Valenciennes, 1833 ( Carangidae ) ( Smales 2014); and Thunnus orientalis (Temminck and Schlegel, 1844) ( Scombridae ) (this study).

Description. Male. Trunk cylindrical, elongate ( Fig. 1A ), 5.77–7.66 mm × 428–673 µm. Proboscis cylindrical, elongate, 1595–1617 µm × 175–192 µm, covered with 23–25 hooks in 12–13 rows ( Fig. 1B ). Basal hooks distinctly large. Trunk spines short, thick. Regions covered with spines were divided into two ( Fig. 1C ), distributed within length of proboscis receptacle. Proboscis receptacle thick, double-walled, elongate, 1389–2199 µm × 203–216 µm. Lemnisci shorter than proboscis receptacle, 1159–1396 µm (n = 2). Testes two, oval, tandem in line. Anterior testis 508–1469 µm × 275– 504 µm. Posterior testis 541–669 µm× 335–440 µm. Cement glands four, tubular. Saefftigen’s pouch 833–984 µm in length (n = 2). Copulatory bursa not everted.

Remarks. The cylindrical trunk, anterior trunk spines, elongate proboscis, enlarged basal proboscis hooks, and four tubular cement glands in the present material indicate its affiliation in Rhadinorhynchus ( Amin et al. 2019b) . Rhadinorhynchus seriolae can be distinguished from other congeners by i) trunk spines distributed in two fields, ii) about 24 proboscis hooks in about 12 rows, and iii) lemnisci shorter than the proboscis receptacle ( Amin et al. 2011; Smales 2014). Thunnus orientalis is herein identified as a new host for R. seriolae .

Records of specimens identified as R. seriolae exist in addition to those listed in the synonym list. Ichihara et al. (1968) identified acanthocephalans from mackerel in Sagami Bay as Nipporhynchus seriolae (= R. seriolae ). They further claimed that the specimen identified as R. japonicus in Kanda (1958) was a synonym of N. seriolae . This identification was questioned by Amin and Heckmann (2017). As a basis for their doubt, they cited the fact that the hook arrangement differs from the original description of R. seriolae . Amin et al. (2011) have also determined that R. japonicus is a valid name. Furthermore, in the original description of R. japonicus ( Fujita 1920) , the arrangement of proboscis hooks was written as 10 rows × 17–18 hooks in each row, while R. japonicus in Kanda (1958) and N. seriolae in Ichihara et al. (1968) was 16–18 rows × 20–25 hooks in each row. The acanthocephalans in Kanda (1958) and Ichihara (1968) resemble R. ditrematis (15–16 × 24) ( Yamaguti 1939) rather than R. seriolae or R. japonicus , but we have not seen the actual specimens, so we cannot be certain. Based on the above situation, we agree with Amin and Heckmann (2017) and speculate that N. seriolae in Ichihara et al. (1968) is a misidentification. Therefore, we do not include Ichihara et al. (1968) and Kanda (1958) in the synonym list for R. seriolae in this paper.

Figures

Fig. 1. Line drawings of Rhadinorhynchus seriolae (Yamaguti, 1963). A, Whole body of a male (one of three specimens of ICHUM 8571); B, proboscis of a male (one of three specimens of ICHUM 8571); C, line drawings showing trunk spines in three specimens in ICHUM 8571, arrowhead indicates the border of two regions of trunk spines. Abbreviations: At, anterior testis; Cg, cement glands; Lm, lemniscus; Pb, proboscis; Pr, proboscis receptacle; Pt, posterior testis; Sp, Saefftigen’s pouch.