Branchiostegus sanae, Huang & Chen & Ke & Zhang, 2025

Branchiostegus sanae sp. nov.

Type materials.

Holotype. • MBM 287909, 350.1 mm SL, male, 17.8 ° N, 110.5 ° E, northern South China Sea , China, 13 March 2023, purchased by Chi Zhang, in IOCAS (Fig. 1 View Figure 1 ). GoogleMaps

Paratypes. • IOZ 233304, 313.5 mm SL, sex uncertain, 17.8 ° N, 110.5 ° E, northern South China Sea , China, 13 March 2023, purchased by Chi Zhang, in IOZ GoogleMaps ; • SCSMBC 031014 , 263.9 mm SL, sex uncertain, 17.8 ° N, 110.5 ° E, northern South China Sea , China, 13 March 2023, purchased by Chi Zhang, in SCSIO GoogleMaps ; • SNHM –Hfi 13217, 295.3 mm SL, sex uncertain, 17.8 ° N, 110.5 ° E, northern South China Sea , China, 13 March 2023, purchased by Chi Zhang, in SNHM GoogleMaps ; • ZJUz 00077 , 304.0 mm SL, sex uncertain, 17.8 ° N, 110.5 ° E, northern South China Sea , China, 13 March 2023, purchased by Chi Zhang, in ZJU GoogleMaps .

Diagnosis.

The species can be distinguished from its congeners in having the following combination of characteristics: a unique white-red bar between the orbit and upper jaw; distal end of upper jaw vertical reaching or exceeding midpoint of orbit; yellow predorsal ridge with dark rim; dorsal fin membrane translucent greyish, with spines darker; dorsal fin spines grey and soft rays yellow; about 16 dark vertical stripes on each side; longest dorsal fin soft ray long, 20.6–22.7 % in SL; no black spots on base of scales; and caudal fin nearly truncated, upper part pale orange mixed with yellow stripes, and lower part dark grey with inconspicuous yellow blotch near base.

Description.

Morphometric measurements and counts are summarized in Table 2 View Table 2 . Body moderately elongate and compressed. Body depth (BD) is almost equal to or slightly shorter than head depth. Predorsal ridge (stronger in large individuals) extending vertically near center of eye. Mouth terminal, oblique; distal end of upper jaw vertical reaching or exceeding midpoint of orbit. Head moderately enlarged; anterior profile straight. Eyes very close dorsolaterally to forehead contour. Orbit diameter large (25.3–34.9 % in HL), subequal to or longer than suborbital depth. Anterior nostrils tubular, with a cutaneous tongue-shaped flap on its posterior rim and located closer to the snout than anterior margin of orbit while posterior nostril oval-like without fleshy flap and located about mid-point between snout and anterior margin of the orbit. Both jaws with 3 or 4 rows of irregular canine-like teeth, with 17–20 of these canines enlarged and primarily distributed in central front and near sides. An irregular villiform teeth band on upper jaw. No teeth on palatine, vomer, or tongue. Posterior margin of preopercle serrated; a few serrations extend to ventral margin, rest of ventral margin smooth.

Cheeks, opercle, nape, and body scaled. Scales on cheek, opercle and near breast cycloid and ctenoid remain parts; 6 or 7 diagonal scale rows on cheek; scales enlarged at second, third, and fourth rows; diameter of largest cheek scales 4.7–5.0 in orbit diameter (OD). Dorsal-fin origin above pectoral-fin base; first spine shortest, length 1.0– 1.9 in OD; length of 2 nd to 7 th spines almost equal, longer than 1 st. First dorsal soft ray shortest, length 1.2–1.7 in OD, 13 th dorsal-fin soft ray longest 0.4–0.5 in OD, 15 th dorsal-fin soft ray shortest; lengths of soft rays length gradually increase from the 1 st to 13 th, rapid decreases in 13 th to 15 th soft rays; dorsal-fin soft rays longer than all spines and peduncle depth except 15 th soft ray, only 13 th soft ray reaching caudal-fin base. Pectoral fin lanceolate, its base located just posterior to preopercle margin, reaching to anal-fin origin; 1 st to 7 th soft rays lengthening; 7 th soft ray longest, 1.1–1.4 in head length (HL); 8 th soft ray discontinuously shortening, 1.6–1.8 in HL; under 8 th soft ray, pectoral-fin soft rays evenly shortening. Pelvic-fin triangular, short, extending to midpoint of its origin to anus; pelvic-fin spine 0.7–0.9 in OD; 2 nd soft ray longest, 0.6–0.7 in OD. Caudal peduncle depth 2.2–2.9 in BD, shorter than its length. Caudal fin almost truncate but slightly emarginate.

When fresh, head and body are plum-colored, with ventral side lighter and dorsal aspect darker. Distinctive red vertical stripe present beneath eye, closely followed by a white band anteriorly. Snout Indian red; cheek region lighter colored. Upper part of operculum rosy brown. Plum vertical stripes taper from dorsal to ventral sides. Base of dorsal-fin spines bear gold spots, with spines and interstitial membranes dark grey. Soft rays of dorsal fin gold, yet their bases grey. Base of pectoral fins with slightly darker dark-red blotches covered by pectoral fins, and fin rays grey. Base of caudal fin paler orange, with upper 2 / 5 tinged with yellow and lower 3 / 5 dark grey. Pelvic and anal fins milky white, but distal ends of 12 th, 13 th, and 14 th anal-fin soft rays grey-black.

Distribution and habitat.

The fishing area was at approximately the coordinates 17.8 ° N, 110.5 ° E in the South China Sea, on the northern slope between Lingshui, Hainan Island and Xisha Islands, at a depth of about 150–300 m (Fig. 2 View Figure 2 ).

Etymology.

The name sanae refers to the heroine’s name, San in Hayao Miyazaki’s film Princess Mononoke, who has similar red under-eye stripes to this species and symbolizes the ideas and appeals of harmonious coexistence between man and nature that we want to share ( Miyazaki 1997).

Common name.

Both the Chinese and English common names of this species are derived from the title of the film and align with the common name used by Chinese fishermen, “ 鬼马头鱼 ” (Ghost horsehead fish), due to the unusual cheek patterns of this species.

Phylogenetic analysis

Here we present the most comprehensive molecular phylogeny of Branchiostegus to date, which includes 10 of the 18 known species and the new species, B. sanae sp. nov. (Fig. 3 View Figure 3 ) The approximately-maximum-likelihood phylogenetic tree has bootstraps value exceeding 0.731 at every node in the backbone of the tree. The tree indicates that all B. sanae specimens we collected in this study form a monophyletic clade sister to all species but B. saitoi and B. doliatus . The southwestern Indian Ocean species B. doliatus appears to be a clade sister to all other species of Branchiostegus included in our analysis. The rest of the analyzed species occur in the western Pacific Ocean, which is the center of distribution of the genus. COI-based molecular species delimitation methods also indicate that B. sanae is a genetically distinct species (see Suppl. material 2).