Rhadinorhynchus laterospinosus

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 : 174-176

Rhadinorhynchus laterospinosus

Amin, Heckmann, and Ha, 2011 ( Fig. 2 )

Rhadinorhynchus laterospinosus Amin Heckmann, and Ha, 2011: 72 , 73, figs 21–26 (Cat Ba Island, Halong Bay, Vietnam); Amin et al. 2019a: 4, 8, figs 1–15 (Binh Thuan, Vietnam; Hai Phong, Vietnam; Nha Trang, Vietnam; Quang Binh, Vietnam); Lisitsyna et al. 2023: 3, figs 1–2 (Budai Harbor, Taiwan; off Taipei, Taiwan; off Yilan, Taiwan).

Material examined. Ten specimens, ICHUM 8572– 8581.

Type locality. Off Cat Ba Island (Halong Bay, Vietnam) ( Amin et al. 2011) .

Other localities. Budai Harbor (Taiwan) ( Lisitsyna et al. 2023); off Binh Thuan ( Vietnam) ( Amin et al. 2019a); off

Hai Phong ( Vietnam) ( Amin et al. 2019a); off Nah Trang (Khanh Hoa, Vietnam) ( Amin et al. 2019a); off Quang Binh ( Vietnam) ( Amin et al. 2019a); off Taipei (Taiwan) ( Lisitsyna et al. 2023); off Tosa-Shimizu ( Kochi, Japan) (this study); off Yilan (Taiwan) ( Lisitsyna et al. 2023).

Type host. Balistes sp. ( Balistidae ) ( Amin et al. 2011).

Other hosts. Alectis ciliaris Bloch, 1787 ( Carangidae ) ( Amin et al. 2019a); Auxis rochei (Risso, 1810) ( Scombridae ) ( Amin et al. 2019a); Auxis thazard (Lacepède, 1800) ( Scombridae ) ( Amin et al. 2019a; this study); Katsuwonus pelamis (Linnaeus, 1758) ( Scombridae ) ( Lisitsyna et al. 2023); Leiognathus equulus (Forsskål, 1775) ( Leiognathidae ) ( Amin et al. 2019a); Lutjanus bitaeniatus (Valenciennes, 1830) ( Lutjanidae ) ( Amin et al. 2019a); Megalaspis cordyla (Linnaeus, 1758) ( Carangidae ) ( Amin et al. 2019a); Nuchequula flavaxilla Kimura, Kimura, and Ikejima, 2008 ( Leiognathidae ) ( Amin et al. 2019a); Scomber australasicus Cuvier, 1832 ( Scombridae ) ( Lisitsyna et al. 2023); Trichiurus lepturus Linnaeus, 1758 ( Trichiuridae ) ( Lisitsyna et al. 2023); and Tylosurus sp. ( Belonidae ) ( Amin et al. 2019a).

Description. General. Trunk cylindrical, elongate ( Fig. 2A ). Proboscis cylindrical, elongate, with 15–16 hook rows and 22–24 hooks per row ( Fig. 2B ). Basal hooks distinctly large. Trunk spines distributed in separated area of anterior end of trunk, connected with a few lateral spines ( Fig. 2C ). Proboscis receptacle elongate, double-walled. Lemnisci unclear. Genital pore opening subterminally.

Male (n = 3). Trunk cylindrical, elongate, 8.31–9.32 mm × 617–806µm. Proboscis cylindrical, elongate, 1509– 2240 µm × 149–296 µm. Trunk spines distributed in separated area of anterior end of trunk ( Fig. 2C ), bridged with a few lateral spines. Proboscis receptacle elongate, double-walled, 1970–3201 µm × 286–434 µm. Testes tandem, oval. Anterior testis 1049–1147 µm × 373–586 µm. Posterior testis 906–1305 µm × 402–590µm. Cement glands four, tubular, tandem in two rows. Saefftigen’s pouch fusiform, 1391 µm in length (n = 1). Copulatory bursa 678–860 µm in width.

Female (n = 7; one of them was damaged). Trunk cylindrical, elongate, 11.70–20.55 mm × 543–872 µm. Proboscis cylindrical, elongate, 1190–1971 µm × 147–311 µm. Trunk spines same as male. Proboscis receptacle elongate, double-walled, 2767–4621 µm × 176–330 µm. Uterus elongate ( Fig. 2D ), 2652–4750 µm × 64–314 µm.

Remarks. The generic placement of this material in Rhadinorhynchus is obvious, due to its cylindrical trunk anteriorly with spines as well as the four tubular cement glands ( Amin et al. 2019a). It can be identified as R. laterospinosus because i) the trunk spines are distributed in two regions, and they are connected to each other with several spines; and ii) the number of proboscis hook rows is 15–16 and 22–24 in per row ( Amin et al. 2011, 2019a). Rhadinorhynchus laterospinosus was originally described by Amin et al. (2011) based on a single female specimen, obtained from a trigger fish Balistes sp. in Vietnam. Later, Amin et al. (2019a) redescribed the morphological characteristics based on male and female specimens obtained from various fishes in Vietnam, including the frigate tuna A. thazard , and Lisitsyna et al. (2023) added the record of this species from Taiwan. Our specimens from Tosa-Shimizu (Kochi) represent the first record of R. laterospinosus from Japan, expanding the known distribution range of the species northeastward for about 1400 km.

Phylogeny

The phylogenetic tree ( Fig. 3 ) reconstructed in this study showed that R. seriolae would be closely related to R. hiansi Soota and Bhattacharya, 1981 and R. dorsoventrospinosus Amin, Heckmann, and Ha, 2011 ; the Japanese population (represented by the present material from Kochi) of R. laterospinosus formed a clade with Taiwanese and Vietnamese one and they would be closely related to each other.

The genetic distances between R. laterospinosus from Japan and Vietnam were 0.55% (COI p-distance and K2P; Table 2) and 0.0% (18S p-distance and K2P; Table 3), while between Japan and Taiwan were 0.4% (COI p-distance and K2P; Table 2) and 0.0% (18S p-distance and K2P). Those between R. seriolae and R. hiansi were 2.2% (COI p-distance; Table 2) to 2.3% (COI K2P; Table 2) and 0.0% (18S p-distance and K2P; Table 3); between R. seriolae and R. dorsoventrospinosus were 2.8% (COI p-distance and K2P).

Figures

Fig. 2. Line drawings of Rhadinorhynchus laterospinosus Amin, Heckmann, and Ha, 2011. A, Whole body of a male (ICHUM 8572); B, proboscis of a male (ICHUM 8572); C, distribution of trunk spines (ICHUM 8575); D, female genital organ (ICHUM 8575). Abbreviations: At, anterior testis; Cb, copulatory bursa; Cg, cement gland; Pb, proboscis; Pr, proboscis receptacle; Pt, posterior testis; Ub, uterine bell; Ut, uterus; Vg, vagina.

Fig. 3. A molecular phylogenetic tree reconstructed with maximum-likelihood method (ML). Nodal support values indicate bootstrap value (BS) by ML/Bayesian posterior probability (BPP) by Bayesian inference (BI). Where the trees drawn by ML and BI differ, BPP values are indicated by a hyphen “-”.