Pegasus nanhaiensis Zhang, Wang & Lin, 2020

Zhang, Rongrong, Wang, Xin, Wan, Shiming, Ma, Shaobo & Lin, Qiang, 2020, A new species of Pegasus (Syngnathiformes: Pegasidae) from the South China Sea, Zootaxa 4894 (4), pp. 521-534 : 523-529

Pegasus nanhaiensis Zhang, Wang & Lin , sp. nov.

English name: Humpback sea moth

Figure 1

Holotype. TMBC 030695 , 61.7 mm SL, Yangjiang , northern South China Sea, China, sta. 21°27'21''N, 112°28'22''E, 20 m depth, local bottom trawl, 20 July 2019.

Paratypes. TMBC030696 – TMBC030698 (3 specimens, 47.1–55.2 mm SL), same data as for the holotype . TMBC030699 – TMBC030703 (5 specimens, 53.8–62.3 mm SL), Yangjiang , northern South China Sea, sta. 21°25'38''N, 112°9'42''E, 23 m depth, bottom trawl, 20 July 2019 . TMBC030704 – TMBC030707 (4 specimens, 53.3–61.5 mm SL), Beihai , northern South China Sea, sta. 21°11'41''N, 109°12'8''E, 17 m depth, bottom trawl, 28 July 2019 . TMCN030708 – TMBC030711 (4 specimens, 52.6–58.0 mm SL), Beihai , northern South China Sea, sta. 21°18'2''N, 108°44'32''E, 19 m depth, bottom trawl, 1 August 2019 .

Diagnosis. The size and general appearance of P. nanhaiensis are similar to those of P. laternarius ( Fig. 2 ). However, P. nanhaiensis is readily distinguished from all other species of the genus Pegasus by the following combination of characteristics: A rounded hump-like tubercle on each of dorsal plates I, II, and III ( Fig. 3A ); clear hexagonal patterns in surface dorsal plate with a clear boundary; and two paired caudolateral plates overlapping the junctions between tail rings II and III, and IV and V ( Fig. 3C ). In comparison, P. laternarius has a pointed, roughly triangular tubercle on each of dorsal plates I, II, and III ( Fig. 3B ), and three paired caudolateral plates overlapping the junctions between tail rings II and III, III and IV, and IV and V ( Fig. 3D ). In P. nanhaiensis , we also observed the formation of a bulge at the margin of the ventral plate that connected to the paired pelvic fins, and four strong rounded tubercles in the concave margin of the occipital.

Description. Morphometric data of 17 Pegasus nanhaiensis and 17 Pegasus laternarius are provided in Table 1. A large male with intact body was designated as the holotype (TMBC030695, SL 61.7 mm). Sexual dimorphism in rostrum length (longer in males) was commonly found in P. laternarius , E. papilio ( Palsson & Pietsch, 1989) , and E. draconis ( Jungersen, 1915) . In this study, the morphological characteristics of male and female species were measured separately. Pegasus nanhaiensis: Body depth 16.5–20.9% SL (male), body depth 16.1–20.0% SL (female). Rostrum of male club-shaped, surface with denticle-bearing ridges, length 13.9–17.4% SL, rostrum width at tip 3.0–4.3% SL. Rostrum of female short, tetragonal, denticle-bearing ridges meeting anteriorly to form a sharp point, length 4.8–6.3% SL, rostrum width at tip 1.0–1.6% SL. Sexual dimorphism in rostrum length of P. nanhaiensis is very obvious, which is also found in P. laternarius ( Palsson & Pietsch, 1989) . Carapace length 48.6–53.2% SL, prepectoral width 40.3–46.0% SL, interpectoral width 29.7–34.9% SL, carapace width 28.8–34.7% SL, tail length 46.7–52.8% SL (male). Carapace length 51.4–54.5%SL, prepectoral width 44.4–47.5% SL, interpectoral width 34.0–36.3% SL, carapace width 34.8–37.0% SL, tail length 45.1–49.8 % SL (female). Orbit length 9.2–11.3% SL, interorbital width 9.1–11.2% SL, head width 26.7–31.8% SL (male). Orbit length 9.7–10.8% SL, interorbital width 8.7–10.7% SL, head width 30.2–32.4% SL (female).

The body is depressed and encased in bony plates. Dorsolateral carapace plates each with a weak, posteriorly directed tubercle; ventrolateral plates with weak tubercles on lateral edges. The eyes are not visible in ventral view. Two rows of humps are arranged on the dorsal plate. Bone staining showed that the carapace osteological structure of P. nanhaiensis was the same as that of P. laternarius . The carapace comprises three paired dorsal plates and four paired dorsolateral plates ( Fig. 3A, B ). Carapace surface with 3 paired, rounded hump-like tubercles on each of dorsal plates I, II, and III. The tail has 11 rings with bulges on both sides, 9th and 10th rings fused together, anteriormost 8 rings can swing freely. The dorsal and anal fins are short and opposite one another, each with 5 unbranched soft rays, located on caudal rings II–IV. The wing-like pectoral fins are relatively large and horizontal, composed of 11 spinous rays, and the fifth ray is thicker compared to adjacent rays. A pair of finger-like pelvic fins is present, each with 1 spine and 2 rays. The caudal fin consists of eight rays. Last tail ring without spine on dorsal surface.

Coloration. In the dry state, dorsal and lateral body surfaces dark brown; clear hexagonal patterns visible on the carapace with distinct boundaries; ventral surface light brown. The first four segments of the tail rings are darker in color than the ones that follow. Pectoral fins with several, irregular rows of brown spots. On the head, small dark spots are scattered between the interorbit and the tip of the rostrum ( Fig. 4 ). In lateral view, the black spots extend from the rostrum to the fourth caudal ring. In life, the surface of the body is glossy, some individuals have brown spots on the dorsal carapaces.

Etymology. The specific name, nanhaiensis , refers to the South China Sea, where the holotype of this species was collected.

Distribution. Known from the holotype and paratypes, trawled from mud bottoms at 17–23 m depth off the coastal waters of Yangjiang and Beihai, northern South China Sea ( Fig. 5 ).

Geometric Morphometry. An assessment of the shape of the carapace and the tubercle was conducted on specimens taken from the five sites in the South China Sea using a geometric morphometric approach. A total of 18 landmarks were selected from the dorsal contour and ridgeline ( Fig. 6A, B ).

The scores of the first and second principal components (PCs) of 103 individuals of P. laternarius and P. nanhaiensis were extracted and plotted. PCA results showed that the specimens collected in Yangjiang and Beihai were significantly different from those collected in Shantou, Wailingding, and Sanya in morphological variation of the dorsal carapace ( Fig. 6A, B ). The raw data for principal component analysis are presented in Table S1.

Molecular analysis. Two partial gene fragments (533 bp of 16S rDNA and 585 bp of COI) were successfully obtained from 31 P. laternarius individuals and 17 P. nanhaiensis individuals. The phylogenetic relationships of P. nanhaiensis , P. laternarius , P. volitans , and P. tetrabelos were reconstructed using the Bayesian method based on the combined 16S rDNA and COI partial gene fragments ( Fig. 7 ). To correspond the genetic data to the individuals of each species, the 16S rDNA GenBank accession number of each individual was displayed in the phylogenetic tree. Eurypegasus draconis was selected as an outgroup due to its close relationship with Pegasus ( Herold & Clark, 1993) . All P. nanhaiensis clustered within a group supported by 100% Bayesian posterior probabilities. It formed a sister group to a group containing all specimens of P. laternarius indicating that P. nanhaiensis is an independent lineage ( Fig. 7 ). The average intraspecific genetic distance estimated between different populations of P. laternarius and P. nanhaiensis ranged from 0.0002 –0.0005, whereas the average interspecific genetic distance estimated between P. nanhaiensis and P. laternarius ranged from 0.0351 –0.0353 ( Table 2), which suggested a distinct interspecies differentiation between P. laternarius and P. nanhaiensis .

Figures

FIGURE 1. Holotype of Pegasus nanhaiensis in (A) dorsal, (B) lateral, and (C) ventral views, TMBC030695 (61.7 mm SL), Yangjiang, northern South China Sea, China, 20 July 2019.

FIGURE 2. Specimen of Pegasus laternarius in (A) dorsal, (B) lateral, and (C) ventral views, TMBC030715 (58.4 mm SL), Shantou, northern South China Sea, China, 20 July 2019.

FIGURE 3. Comparison of morphological characteristics of carapace, and tail of two species of Pegasus with bone staining. Panels A and C show the dorsal ridge processes (arrowed), and tail spines (arrowed) of Pegasus nanhaiensis, TMBC030710, 56.9 mm SL. Panels B and D show the dorsal ridge processes (arrowed), and tail spines (arrowed) of Pegasus laternarius, TMBC030729, 61.1 mm SL.

FIGURE 4. Dorsal view of the head of (A) Pegasus nanhaiensis (TMBC030695, 61.7 mm SL) and (B) Pegasus laternarius (TMBC030715, 58.4 mm SL).

FIGURE 5. Sampling sites of Pegasus nanhaiensis sp. nov. (circle) and Pegasus laternarius (triangle).The red circle represents the type locality of Pegasus nanhaiensis.

FIGURE 6. Principal components analysis (PCA) scatterplot of geometric morphometry data of (A) the dorsal-shape contour and (B) dorsal-ridge shape in Pegasus nanhaiensis and Pegasus laternarius.

FIGURE 7. Molecular identification of Pegasus species based on the combined 16S rDNA and COI sequences using Bayesian approaches. Eurypegasus draconis was selected as the outgroup taxon. Bayesian posterior probabilities are shown above the nodes.