Symphurus oxyrhynchus, Lee, 2022

Lee, Mao-Ying, 2022, A new species of deep-water tonguefish (Pleuronectiformes: Cynoglossidae: Symphurus) from the western North Pacific Ocean, Zootaxa 5189 (1), pp. 233-242 : 234-239

Symphurus oxyrhynchus sp. nov.

(English name: Sharpnose tonguefish)

( Figs. 1–4 ; Table 1 )

Holotype. NSMT-P 57352 , mature female, 101.3 mm SL, off Kochi, Tosa Bay , Japan, 744–786 m, 33º10.63’– 33º11.36’ N, 133º53.79’– 133º55.35’E, 11 December 1998.

Paratype. ASIZP0061780 , male, 87.4 mm SL, South China Sea, off SW Taiwan, otter trawl, 718–852 m, 22º05.16’– 22º10.73’ N, 120º14.10’ E, Ocean Researcher I, CD 139, 23 November 2001 .

Diagnosis. Symphurus oxyrhynchus sp. nov. is distinguished from all congeners by the combination of: 1–2–2– 1–2 ID pattern, 14 caudal-fin rays, 9 abdominal vertebrae, 52 total vertebrae, 5 hypurals, 93 dorsal-fin rays, 80–81 anal-fin rays, 87–89 longitudinal scale rows, 31 transverse scales, 18 scale rows on head posterior to lower orbit, small eye (7.5–8.0% HL) with relatively large pupil (78–85% ED), square snout, projecting anteriorly, with the ocular side uniformly yellow to dark brown with intense pigmentation on body areas overlying dorsal- and anal-fin pterygiophores, outer surface of opercle bluish-black, and with the blind side sharing the same coloration and also the same intensity overlying the pterygiophore areas.

Description. Meristic characters and proportions of morphometric features are summarized in Table 1 . Symphurus oxyrhynchus sp. nov. is a medium-sized species; reaching sizes to at least 101.3 mm SL. Predominant ID pattern 1–2–2–1–2 (2/ 2 specimens) ( Fig. 1 ). Caudal-fin rays 14 (one specimen with 15 caudal-fin rays). Dorsal-fin rays 93. Anal-fin rays 80–81. Pelvic-fin rays 4. Total vertebrae 52; abdominal vertebrae 9 (3 + 6) ( Fig. 1 ). Hypurals 5. Longitudinal scale rows 87–89. Scale rows on head posterior to lower orbit 18. Transverse scale rows 31.

Body moderately deep; maximum depth in anterior one-third of body; body depth tapering gradually from anterior to posterior. Preanal length smaller than body depth. Head wide; head width slightly greater than head length (HW/HL 1.01–1.03). Upper head lobe narrower than lower head lobe and shorter than postorbital length (UHL/ LHL= 0.94–0.98). Lower opercular lobe of ocular-side slightly narrower than upper opercular lobe. Snout square and projecting anteriorly, its length much greater than eye diameter (SNL/ED 2.84–2.87). Dermal papillae well developed, present on blind side snout and lower part of chin. Ocular-side anterior nostril tubular and short, usually not reaching anterior margin of lower eye when depressed posteriorly. Ocular-side posterior nostril a small rounded tube located between upper and lower eye. Blind-side anterior nostril tubular and elongate, easily distinguishable from dermal papillae; blind-side posterior nostril a shorter posteriorly-directed tube situated posterior to vertical at rear margin of jaws. Jaws short; posterior margin of upper jaw usually reaching point between verticals through anterior margin and midpoint of lower eye. Eyes separate, round and extremely small; with two to three rows of small ctenoid scales in interorbital space, and with some small scales covering upper aspects of eye. Pupillary operculum absent. Dorsal-fin origin located at point between verticals through anterior margin and midpoint of upper eye. No scales present on dorsal- and anal-fin rays on either side. Caudal fin short, with several rows of ctenoid scales on base of fin.

Four to five rows of well-developed teeth on blind-side dentary; two to three rows of well-developed teeth on blind-side premaxilla. One row of sharply, pointed, well-developed teeth on both ocular-side dentary and premaxilla.

Pigmentation ( Figs. 2–3 ). Ocular-side background coloration generally yellow to dark brown with greatest intensity on body areas overlying dorsal- and anal-fin pterygiophores. Head coloration similar to that on body. Outer surface of both opercles bluish-black. Posterior margin of opercle darker, black and easily distinguishable from bluish-black regions of opercle. Inner surfaces of opercles with small dark-brown or black dots. Lips and chin region yellow to light brown, margins of lips unpigmented. Ocular-side anterior nostril light yellow. Upper aspects of eyes, and eye socket bluish, pupil light bluish. Blind side background coloration the same as the ocular-side background coloration, uniformly yellow to dark brown with darker, with greater intensity on the area overlying dorsal- and anal-fin pterygiophores. Peritoneum bluish-black, clearly observed through abdominal wall on both sides.

Fin rays of dorsal, anal, and pelvic fins uniformly yellow to dark brown with black margins; basal regions of fin rays brown. Fin membrane usually faded, and transparent in whole membrane area. Coloration of blind-side fin rays yellow to dark brown, with darker coloration covering their basal margins.

Size and sexual maturity. Of two specimens examined, one is a male of 87.4 mm SL, while the other is a mature female of 101.3 mm SL with elongate, but not gravid, ovaries.

Distribution & Ecology. Symphurus oxyrhynchus is currently known from only two specimens, one collected from Tosa Bay, Japan; and the other collected from off Siao-Liouciou, South China Sea, Taiwan ( Fig. 4 ). These specimens were collected from deep waters between 718 and 852 m depths. It is expected that this species has wider distributions, horizontally and vertically.

Small crustaceans, snails and bivalves were observed in the digestive systems of the holotype ( Fig. 1A ). Little else is known regarding the biology of this species.

Etymology. The name oxyrhynchus , derived from the Greek, oxy meaning sharp, and rhynchus, meaning snout, in reference to the relatively sharp, pointed snout of this species compared with those of congeners.

Comparisons. Symphurus oxyrhynchus is easily distinguished from all other congeners, except S. fuscus Brauer , S. macrophthalmus Norman , and S. schultzi Chabanaud , by the combination of a 1–2–2–1–2 ID pattern ( Fig. 1 ), 9 abdominal vertebrae, and 14 caudal-fin rays. Symphurus oxyrhynchus is easily separated from S. fuscus by having fewer dorsal- (93 vs. 105 in S. fuscus ) and anal-fin rays (80–81 vs. 93 in S. fuscus ), and fewer total vertebrae (52 vs. 58 in S. fuscus ) than are found in S. fuscus . These species, known from limited specimens, are actually distributed in different oceans, with S. oxyrhynchus currently known from off Taiwan and Japan, western Pacifc, while S. fuscus was collected from off east Africa, western Indian Ocean. Both of these need further investigation for more precise species definitions and understanding the range of morphological variation of the species. Compared with S. macrophthalmus and S. schultzi , S. oxyrhynchus has similar but slightly higher counts of dorsal- (93 vs. 87 in S. macrophthalmus , and 85–88 in S. schultzi ) and anal-fin rays (80–81 vs. 75 in S. macrophthalmus , and 72–75 in S. schultzi ), and total vertebrae (52 vs. 48 in S. macrophthalmus , and 48–50 in S. schultzi ). Symphurus oxyrhynchus also differs from both species in having an obviously smaller eye (7.5–8.0% HL vs. 21.1% HL in S. macrophthalmus , and 13.3–18.9% HL in S. schultzi ) with a larger pupil (pupil diameter/eye diameter 78–85% vs. 54% in S. macrophthalmus , and 61.9–68.4% in S. schultzi ).

Symphurus oxyrhynchus is also similar to S. bathyspilus Krabbenhoft and Munroe , S. multimaculatus Lee, Munroe and Chen , and S. thermophilus Munroe and Hashimoto in sharing similar meristic features, but is easily distinguished from these species by its 1–2–2–1–2 ID pattern (vs. 1–2–2–2– 2 in these others). In morphometric measurements, S. oxyrhynchus differs from these other species in having a much smaller eye (7.5–8.0% HL vs. 12.2–16.3% HL in S. bathyspilus , 9.1–10.1% HL in S. multimaculatus , and 10.2–16.3% in S. thermophilus ), and by its generally yellow to dark-brown coloration with intense coloration on body areas overlying the dorsal- and anal-fin pterygiophores on both sides (vs. uniformly lighter and white blind side in these other three species, and with pepper-dots present in S. bathyspilus and S. multimaculatus , and the ocular side of both in S. bathyspilus and S. thermophilus usually has crossbands, and do not have intense coloration overlying the pterygiophore regions). Symphurus oxyrhynchus also differs from S. bathyspilus in having a longer snout (20.2–21.3% HL vs. 12.9–19.7% HL in S. bathyspilus ) and a much shorter anterior nostril, not reaching the lower eye when depressed (vs. elongate anterior nostril, usually reaching the lower eye when depressed). Symphurus oxyrhynchus is further distinguished from S. multimaculatus in having fewer scale rows on the head posterior to the lower orbit (18 vs. 21–24 in S. multimaculatus ), fewer transverse rows of scales (31 vs. 45–48 in S. multimaculatus ), and fewer longitudinal scales (87–89 vs. 102–108 in S. multimaculatus ), a more slender body (25.2–26.5% SL vs. 28.6–35.1% SL in S. multimaculatus ), narrower head (20.5–21.0% SL vs. 24.5–30.2% SL in S. multimaculatus ), a with a smaller ratio of HW/HL (HW/HL=1.01–1.03 vs. HW/HL= 1.26–1.50 in S. multimaculatus ), a longer predorsal length (22.1–25.8% HL vs. 15.2–19.3% HL in S. multimaculatus ), narrower upper head lobe (10.2–10.3% SL vs. 14.4–18.8% SL in S. multimaculatus ) that is shorter than the lower head lobe (vs. bigger than lower head lobe in S. multimaculatus ),the snout much longer than the eye (SNL/ED=2.84–2.87 vs. SNL/ED= 1.54–1.90 in S. multimaculatus ), and in S. oxyrhynchus the pupil is also larger (pupil diameter/eye diameter 78–85% vs 61–72% in S. multimaculatus ).

Symphurus oxyrhynchus also differs from S. thermophilus in having fewer scale rows on the head posterior to the lower orbit (18 vs. 20–24 in S. thermophilus ), fewer transverse scale rows (31 vs. 47–56 in S. thermophilus ), and fewer longitudinal scales (87–89 vs. 100–112 in S. thermophilus ), a more slender body (25.2–26.5% SL vs. 28.4–33.1% SL in S. thermophilus ), narrower head (20.5–21.0% SL vs. 26.2–29.3% SL in S. thermophilus ) that is much smaller than its length (HW/HL=1.01–1.03 vs. HW/HL= 1.18–1.30 in S. thermophilus ), narrower upper head lobe (10.2–10.3% SL vs. 13.8–17.1% SL in S. thermophilus ), a narrower lower head lobe (10.5–10.9% SL vs. 11.7–15.9% SL in S. thermophilus ), and with upper head narrower than the lower head lobe (vs. upper lobe wider than lower head lobe in S. thermophilus ), narrower lower lobe of opercle (20.6–24.6% HL vs. 26.9–36.4% HL in S. thermophilus ), and upper opercular lobe wider than the lower (vs. lower opercular lobe wider than the upper in S. thermophilus ), and larger pupil (pupil diameter/eye diameter 78–85% vs. 55–68% in S. thermophilus ).

Symphurus oxyrhynchus is also similar to S. fallax Chabanaud , S. orientalis (Bleeker) , and S. septemstriatus (Alcock) in having similar or overlapping dorsal- and anal-fin rays, and counts for abdominal and total vertebrae. Symphurus oxyrhynchus differs distinctly from these species in having 14 caudal-fin rays and five hypurals (vs. 12 caudal-fin rays and four hypurals in those species), and a 1–2–2–1–2 ID pattern (vs. 1–2–2–2– 2 in those species).

Figures

FIGURE 1. Radiographs depicting interdigitation patterns (ID patterns) of proximal dorsal-fin pterygiophores and neural spines and numbers of abdominal vertebrae for Symphurus oxyrhynchus sp. nov. A. holotype, NSMT-P 57352. B. paratype, ASIZP0061780.

FIGURE 2. Symphurus oxyrhynchus sp. nov., holotype, NSMT-P 57352, mature female, 101.3 mm SL, collected at 744–786 m in Tosa Bay (33º10.63’–33º11.36’ N, 133º53.79’–133º55.35’E), Japan. A. Ocular-side coloration. B. Blind-side coloration.

FIGURE 3. Symphurus oxyrhynchus sp. nov., paratype, ASIZP0061780, male, 87.4 mm SL, collected at 718-852 m off SW Taiwan (22º05.16’–22º10.73’ N, 120º14.10’ E), South China Sea. A. Ocular-side coloration. B. Blind-side coloration.

FIGURE 4. Geographic distribution of Symphurus oxyrhynchus sp. nov., capture location of holotype indicated by asterisk. Capture location of paratype indicated by solid square.