First records of the seamoth, Pegasus nanhaiensis (Actinopterygii: Syngnathiformes: Pegasidae), from the southern South China Sea, with notes on fresh coloration

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 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.

Methods
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 Description. Measurements are given in Table 1. Body depressed, encased in bony plates. Eyes not visible in ventral view. Rostrum of male long, club-shaped, with many small surface spines; that of female very short, pointed. Mouth small, inferior, toothless. Gill opening restricted to small dorsolateral hole behind head. Two rows each with two small tubercles on dorsum of head. Carapace comprising three pairs of dorsal plates (d 1-3 ), four pairs of dorsolateral plates (dl 1-4 ), paired superior pectoral-fin plates (pp.s.), and two paired extralateral plates (el 1-2 ); rounded hump-like tubercles on each dorsal plate (d 1-3 ); small posteriorly directed tubercles on lateral edges of each dorsolateral plate (dl 1-4 ). [KAUM-I. 47680 with hookshaped tubercle between paired dorsal plates (d 2 ); absent in KAUM-I. 47679 and 47681]. Plastron comprising five paired ventrolateral plates (vl 1-5 ), paired gular plates (g), pectoral plates (p), ventral plates (v), anal plates (a) and inferior pectoral-fin plates (pp.i.) and an unpaired pre-anal plate (ip). Anus located between preanal plate and tail ring I. KAUM-I. 47679 with 6 inwardly directed spines (7 and     . 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). 5 in KAUM-I. 47680 and 47681, respectively) on dorsal surface of ventrolateral plate (vl 1 ). Small central tubercles on each pectoral and ventral plate; interventral and pre-anal plates with bulge, the latter plate with posteriorly directed tubercle; small, posteriorly directed tubercles on lateral edges of each vl 2 -vl 4 . Tail elongate, with 11 tail rings (I-XI); 9 th and 10 th tail rings fused together, anterior 8 rings mobile; small, posteriorly directed tubercles on corners of each tail ring, their tips sharply pointed; tubercles smaller on posterior tail rings; anteriorly directed spines on anterior of tubercles on tail rings IX, X, and XI; two paired caudolateral plates overlapping junctions between tail rings II and III and IV and V; dorsal surface of last tail ring lacking spine. Wing-like pectoral fins large, inserted horizontally, with 11 rays (10 and 12 rays on left and right side, respectively, in KAUM-I. 47679), 5 th ray stout, thicker than other rays. Pelvic fins with 1 spine and 2 rays; each pelvic fin separated without membrane, inserted into an unpaired interventral plate; first spine very long, extended posteriorly. Dorsal and anal fins short, each with 5 soft rays, extending from center of dorsal and ventral tail ring II to center of tail ring IV, respectively.

Discussion
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. Al-though 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. . 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).
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.
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).
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 JPJSC-CB20200009; 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.