Three seamoth specimens (45.5–56.9 mm standard length; SL) (Syngnathiformes: Pegasidae), originally identified as Pegasus laternarius Cuvier, 1829, but now recognized as representing P. nanhaiensis Zhang, Wang et Lin, 2020, a species recently described from the northern South China Sea off Yangjiang and Beihai, China, were obtained at a local fish market in Maha Chai, Samut Sakhon Province, Thailand on 6 July 2012, having been caught in the northern Gulf of Thailand. In addition, single specimens, reported as P. laternarius or Spinipegasus laternarius from Bidong Island, South China Sea off the Malay Peninsula (46.1 mm SL) and from Ko Kradat, Trat Province, eastern Gulf of Thailand (66.1 mm SL), were re-identified here as P. nanhaiensis. Thai specimens and Malaysian record represent the first records of P. nanhaiensis from Thailand and Malaysia, respectively, and from outside Chinese coastal waters. Additionally, the Bidong specimen is the southernmost record for the species. The fresh coloration of P. nanhaiensis is described for the first time.

Pegasus laternarius, distribution, southernmost record, Bidong Island, Malaysia, Gulf of Thailand

The Indo-West Pacific genus Pegasus Linnaeus, 1758, characterized by having 11 tail rings, no spine on the dorsal surface of the last dorsal ring, and the eyes not visible in ventral view (Palsson and Pietsch 1989), includes five valid species, viz., Pegasus lancifer Kaup, 1861, Pegasus laternarius Cuvier, 1829, Pegasus nanhaiensis Zhang, Wang et Lin, 2020, Pegasus tetrabelos Osterhage, Pogonoski, Appleyard et White, 2016, and Pegasus volitans Linnaeus, 1758 (see Zhang et al. 2020; Fricke et al. 2021).

Pegasus nanhaiensis was originally described on the basis of 17 specimens from the northern South China Sea (off Yangjiang and Beihai) (Zhang et al. 2020), no further specimens having been recorded since. However, three specimens, collected from the northern Gulf of Thailand prior to that description, were re-identified here as P. nanhaiensis, two having been reported as P. laternarius by Matsunuma (2013). These three specimens, therefore, represent the first records of P. nanhaiensis from the Gulf of Thailand and the first records outside Chinese coastal waters. In addition, previous records of P. laternarius (or as Spinipegasus laternarius) from the eastern Gulf of Thailand and the eastern Malay Peninsula were re-identified here as P. nanhaiensis. As Zhang et al. (2020) described the coloration of dry specimens only, a fresh color description of P. nanhaiensis is provided here for the first time.

Counts and measurements followed Osterhage et al. (2016) and Zhang et al. (2020). Measurements were made to the nearest 0.1 mm with digital calipers under a dissecting microscope. Standard length is abbreviated as SL. Terminology of body parts and determination of sex followed Palsson and Pietsch (1989). The following description was based solely on the three specimens from the northern Gulf of Thailand (Figs 1–3). Photographs of the lateral view of tail rings I–VI (Fig. 3) were taken with a Nikon D850 camera using the internal focus bracketing function (focus step width 1, number of shots 30); a set of multifocal images were then collated into an overall well-focused composite image using Combine ZP (free software: available at https://combinezp.software.informer.com). Institutional codes follow Sabaj (2020). Comparative material of P. laternarius (6 specimens, 24.5–55.1 mm SL, from Japan) examined in this study are as follows: KAUM–I. 420, female, 55.1 mm SL, east of Sakinoyama, Kataura, Kasasa, Minami-satsuma, Kagoshima, 31°25'44"N, 130°11'49"E, 27 m depth, set net, 6 Mar 2006; KAUM–I. 3234, female, 24.5 mm SL, KAUM–I. 3247, female, 28.0 mm SL, Kaihama Beach, Kasasa, Minami-satsuma, Kagoshima, 31°24'37"N, 130°11'32"E, 0.5 m depth, hand net, 17 Mar 2007; KAUM–I. 17604, female, 37.0 mm SL, off Kouzaki-yama, Kataura, Kasasa, Minami-satsuma, Kagoshima, 31°26'00"N, 130°10'05"E, 36 m depth, set net, 17 Mar 2007; KAUM–I. 31094, male, 36.6 mm SL, east of Sakinoyama, Kataura, Kasasa, Minami-satsuma, Kagoshima, 31°25'44"N, 130°11'49"E, 27 m depth, set net, 13 Mar 2010; KAUM–I. 105955, male, 49.0 mm SL, fish market in Tei, Yasu, Kounan, Kochi, 33°31'42"N, 133°45'14"E, 24 Oct 1981.

The presently reported specimens were consistent with the diagnosis of Pegasus nanhaiensis, provided by Zhang et al. (2020), all having a rounded hump-like tubercle on each of dorsal plates I, II, and III; clear, distinctly bounded hexagonal patterns on the dorsal plates (d_1-3), and dorsolateral plates (dl_1-4); two paired caudolateral plates overlapping the junctions between tail rings II and III and IV and V (Fig. 3); and a bulge on the margin of the ventral plate connecting with the paired pelvic fins. Although the rostrum length in the female and rostrum tip width in males in this study differed slightly compared with the original description (6.9% of SL and 4.9%–5.0% of SL, respectively, in the presently reported specimens vs. 4.8%–6.3% and 3.0%–4.8%, respectively, in the type series; Table 1), such minor differences were regarded here as intraspecific variations. Pegasus nanhaiensis is similar to P. laternarius in sharing 11 tail rings, thickened fifth pectoral-fin ray, the fused 9^th and 10^th tail rings, and a wider carapace (carapace width 28.8%–37.0% of SL in the former, 24.7%–35.8% in the latter), whereas other congeners have 12 (in P. tetrabelos and P. volitans) and 14 (in P. lancifer) tail rings, normal fifth pectoral-fin ray (not thickened; in P. lancifer and P. volitans), the posterior 3 (in P. tetrabelos and P. volitans) and 7 (in P. lancifer) tail rings fused together and a slender carapace (21.3%–28.1% of SL in P. lancifer, 13.5%–18.1% of SL in P. tetrabelos and 12.8%–15.5% of SL in P. volitans). Pegasus nanhaiensis can be distinguished from P. laternarius by the above-mentioned diagnostic characters (the latter with a pointed, roughly triangular tubercle on each of dorsal plates I, II, and III; no hexagonal pattern on dorsal plates; three paired caudolateral plates on tail rings II and III, III and IV, and IV and V) (Palsson and Pietsch 1989; Osterhage et al. 2016; Zhang et al. 2020; this study). In addition, 16S rDNA and COI analyses put P. nanhaiensis into a different clade from P. laternarius, separated by a genetic distance of 3.51–3.53 percentage points (Zhang et al. 2020).

Figure 3. 

Lateral view of tail rings I–VI of Pegasus nanhaiensis (KAUM–I. 47680, male, 56.9 mm SL) stained with cyanine blue. Red arrows indicate caudolateral plates overlapping junctions between tail rings II and III and IV and V, respectively.

Pegasus nanhaiensis was previously known only from the type specimens from the northern South China Sea, off Yangjiang and Beihai, China (Zhang et al. 2020), the three specimens described herein representing the first records of P. nanhaiensis from the Gulf of Thailand. In addition, a single specimen (ZMUC P 842, 66.1 mm SL), reported as P. laternarius by Palsson and Pietsch (1989: 23, fig. 11) from Ko Kradat, eastern Gulf of Thailand and a single specimen (FRLM 55093, 46.1 mm SL), reported as Spinipegasus laternarius (Cuvier, 1829) by Hibino (2021: 14, unnumbered figs.) from off Bidong Island, east off the Malay Peninsula, South China Sea, were re-identified here as P. nanhaiensis, based on clear, distinctly bounded hexagonal patterns on the dorsal plates (d_1-3) and dorsolateral plates (dl_1-4) from their photographs, respectively. The Bidong specimen represents the southernmost record of the species (Fig. 4), suggesting that P. nanhaiensis is widely distributed in coastal waters of the South China Sea.

Figure 4. 

Distributional records of Pegasus nanhaiensis. Yellow stars: type series localities (black arrow: type locality); red circles and striped area: localities of presently reported specimens (specimens from northern Gulf of Thailand were obtained at a fish market; their approximate collection locality indicated).

The coloration of P. nanhaiensis was previously known only from dried specimens (Zhang et al. 2020), the fresh color description of the species being provided here for the first time. Although the dorsal and lateral body surfaces were dark brown and the first four segments of the tail rings darker than the remaining tail rings in the dried specimens (Zhang et al. 2020), the dorsal surface was yellow to dark yellowish-brown and tail rings I–IV and the posterior half of VII and VIII brown (remaining rings yellowish-white) in the presently reported fresh specimens from Thailand.

The clear hexagonal patterns on the surface dorsal plate, found in fresh specimens of P. nanhaiensis (Fig. 1), was lost in preserved specimens (Fig. 2), which became indistinguishable from preserved P. laternarius on this basis (Figs 2 and 5).

Figure 5. 

Dorsal views of preserved specimens of Pegasus laternarius from Japan. A: KAUM–I. 31094, male, 36.6 mm SL; B, KAUM–I. 17604, female, 37.0 mm SL.

We are especially grateful to H. Wada (KPM) for reading the manuscript and giving valuable comments, P. Musikasinthorn (Kasetsart University, Thailand) for donating specimens and G. Hardy (Ngunguru, New Zealand) for reading the manuscript and providing help with English. This study was supported in part by JSPS KAKENHI Grant Numbers 20H03311 and 21H03651; the JSPS Core-to-core CREPSUM JPJSCCB20200009; and the “Establishment of Glocal Research and Education Network in the Amami Islands” project of the Kagoshima University adopted by the Ministry of Education, Culture, Sports, Science, and Technology, Japan.