Symphurus robustus, Lee & Munroe, 2021

Lee, Mao-Ying & Munroe, Thomas A., 2021, Unraveling cryptic diversity among shallow-water tonguefishes (Pleuronectiformes: Cynoglossidae: Symphurus) from the Indo-West Pacific region, with descriptions of five new species, Zootaxa 5039 (1), pp. 1-55 : 40-43

Symphurus robustus n. sp.

(English name: Robust tonguefish)

( Figs. 3 , 11 ; Tables 1–5, 11)

Holotype: BSKU 45132 , male, 60.0 mm SL, Off Kochi, Tosa Bay, Japan, bottom trawl, 90 m, 33º20.33’– 33º20.76’N, 133º36.40’– 133º34.97’E, R / V Toyohata-maru, 22 Oct 1987.

Paratypes. 21 specimens (35.3–67.5 mm SL); off Kochi, Tosa Bay , Japan, collected by R / V Toyohata-maru using bottom trawl: ASIZP0072351 , immature female, 35.3 mm SL, 45 m, 33º16.12’– 33º26.31’N, 133º33.12’– 133º40.60’E, 9 May 1994. ASIZP0072353 , 8 specimens, 51.3–61.8 mm SL, 46 m, 33º25.74’– 33º25.86’N, 133º32.88’– 133º33.22’E, 9May 1994. ASIZP0072354 , 5specimens, 47.9–67.5 mm SL, 64 m, 33º23.86’– 33º24.04’N, 133º33.86’– 133º34.16’E, 4 Apr 1994. BSKU 45128 , mature female, 61.6 mm SL, 90 m, 33º20.33’– 33º20.76’N, 133º36.40’– 133º34.97’E, 22 Oct 1987. BSKU 45129 , male, 60.5 mm SL, 90 m, 33º20.33’– 33º20.76’N, 133º36.40’– 133º34.97’E, 22 Oct 1987. BSKU 45131 , male, 64.9 mm SL, 90 m, 33º20.33’– 33º20.76’N, 133º36.40’– 133º34.97’E, 22 Oct 1987. BSKU 45133 , male, 61.5 mm SL, 90 m, 33º20.33’– 33º20.76’N, 133º36.40’– 133º34.97’E, 22 Oct 1987. BSKU 45448 , mature female, 63.2 mm SL, 60 m, 33º23.73’– 33º24.98’N, 133º31.81’– 133º35.40’E, 21 Apr 1986. BSKU 45459 , mature female, 54.0 mm SL, 45 m, 33º25.29’– 33º25.97’N, 133º32.40’– 133º33.58’E, 9 Jun 1988. BSKU 45464 , mature female, 65.5 mm SL, 60 m, 33º23.99’– 33º24.46’N, 133º32.43’– 133º34.47’E, 22 Jun 1988.

Diagnosis. Symphurus robustus is distinguished from all congeners by the combination of: a 1–2–2–2–2 ID pattern; 12 caudal-fin rays; 9 (3 + 6) abdominal vertebrae; 47–49 total vertebrae; 4 hypurals; 85–88 dorsal-fin rays; 72–76 anal-fin rays; 78–88 longitudinal scale rows; 31–34 transverse scale rows; and 16–18 scale rows on head posterior to lower orbit; moderately wide body (BD= 25.5–28.3% of SL); short preanal length (PAL= 22.2–24.7% of SL); relatively short head (HL= 19.1–21.8% of SL), with its length much shorter than its width (HW/HL= 1.06– 1.20); postorbital length moderately short (POL= 65.8–70.2% of HL); upper head lobe usually larger than lower head lobe; dorsal-fin origin at vertical through posterior margin of upper eye; predorsal length moderately long (PDL= 21.6–28.0% of HL); snout moderately long (SNL= 16.8–21.2% of HL; SNL/ED= 1.55–2.00), and round to obliquely blunt anteriorly; anterior margin of upper eye usually equal to, or slightly in advance of, anterior margin of lower eye; fleshy ridge well developed on posterior part of ocular-side lower jaw; membrane covering both eyes; a membranous flap continuous between ocular-side anterior nostril and lower part of eye; ocular-side pigmentation uniformly yellow to light-brown, usually with 5–7 complete or incomplete crossbands; blind-side pigmentation uniformly white, usually with pepper-dots and relatively few dermal melanophores at bases of dorsal and anal fins; obvious dermal spots on bases of the anteriormost dorsal- and anal-fin rays on both sides; peritoneum bluish-black.

Description. Symphurus robustus ( Fig. 11 ) is a dwarf species known from 22 specimens, the largest of which measures 67.5 mm SL. Meristic characters are summarized in Tables 2–5. Predominant ID pattern 1–2–2–2–2 (20/ 22 specimens). Caudal-fin rays 12. Dorsal-fin rays 85–88. Anal-fin rays 72–76. Pelvic-fin rays 4. Total vertebrae 47–49; abdominal vertebrae 9 (3 + 6). Hypurals 4. Longitudinal scale rows 78–88. Scale rows on head posterior to lower orbit 16–18. Transverse scale rows 31–34.

Proportions of morphometric features presented in Table 11. Body moderately deep; maximum depth in anterior one-third of body usually at point between anus and third anal-fin ray; body with gradual taper posterior to midpoint. Preanal length much shorter than body depth. Head moderately short and wide; head width longer than head length (HW/HL= 1.06–1.20, Mean= 1.09). Upper head lobe wider than lower head lobe (UHL/LHL= 1.05–1.34, Mean= 1.18); shorter than postorbital length. Lower lobe of ocular-side opercle wider than upper opercular lobe; posterior margin of lower lobe projecting slightly beyond posterior margin of upper opercular lobe. Snout moderately long, slightly round to obliquely blunt anteriorly, its length usually much greater than eye diameter (SNL/ED= 1.52–1.99, Mean=1.73). Dermal papillae present and well developed on blind side of snout and chin. Ocular-side anterior nostril tubular and short, when depressed posteriorly usually not reaching anterior margin of lower eye. Ocular-side posterior nostril a small, rounded tube located on snout just anterior to interorbital space. Blind-side anterior nostril tubular and relatively long, easily distinguishable from dermal papillae; blind-side posterior nostril a shorter and wider, posteriorly directed tube situated posterior to vertical at rear margin of jaws. Jaws short and slightly arched; upper jaw length slightly longer than snout length; posterior margin of upper jaw usually extending to point between verticals through anterior margin of pupil and anterior margin of lower eye. Ocular-side lower jaw with well-developed fleshy ridge on its posterior portion. Cheek depth narrow, slightly shorter than, or equal to, snout length. Eyes moderately large (ED= 9.6–12.0% of HL) and oval, contiguous, with membrane covering both eyes; fleshy membranous skin flap connecting eye with ocular-side anterior nostril. Eyes usually equal in position, or with anterior margin of upper eye slightly in advance of anterior margin of lower eye. Pupillary operculum absent. Dorsal-fin origin located at point between verticals through posterior margin of upper eye and point posterior to eye; predorsal length moderately long. Anteriormost dorsal-fin rays obviously shorter than more posterior fin rays. Scales absent on both sides of dorsal- and anal-fin rays. Pelvic fin moderately long; longest pelvic-fin ray, when extended posteriorly, reaching base of fifth anal-fin ray. Posteriormost pelvic-fin ray connected to anal fin by delicate membrane. Caudal fin relatively long, with three rows of ctenoid scales on its base. Scales on both sides of body numerous, strongly ctenoid.

Teeth present and recurved slightly inwards on all jaws, but better developed on blind-side jaws. Ocular-side premaxilla and dentary with single row of sharply pointed, well-developed teeth. Blind-side premaxilla with two to three rows of sharp, recurved teeth. Blind-side lower jaw with three to five rows of well-developed teeth.

Pigmentation of freshly caught specimens. Pattern of body pigmentation generally similar for both sexes at all sizes ( Fig. 11 ). Ocular-side background pigmentation generally light-yellow to light-brown; usually with 5–7 complete or incomplete crossbands. External surface of abdominal area usually bluish-black. Background pigmentation of ocular side of head generally similar to that on body, with dark region behind eyes formed by concentration of dermal melanophores. Ocular side of snout light yellow. Obvious dermal spots at bases of anterior dorsal-fin rays and on the isthmus. Outer surface of ocular-side opercle yellow to brown, with same background pigmentation as that on body and head; margin of opercle darker brown and easily distinguishable from bluish regions of opercle; inner surface of ocular-side opercle and isthmus with small dark-brownish or blackish dots. Ocular-side lips and chin region uniformly yellow to brown, margins of lips pigmented with small melanophores. Ocular-side anterior nostril light-yellow to brown. Upper aspects of eyes and eye sockets light blue with darker spots; pupils bluish-black. Blind side generally white to light-yellow with bluish-black peritoneum; pepper-dots present on body regions overlying pterygiophores of dorsal and anal fins, some specimens also with median longitudinal row of darkly-pigmented melanophores along vertebral axis. Well-developed dermal melanophores also forming single longitudinal row along bases of dorsal and anal fins. Outer surface of blind-side opercle white to light-yellow similar to background pigmentation of blind side. Inner surface of blind-side opercle unpigmented. Fin rays of dorsal, anal, and pelvic fins uniformly yellow to brown; basal regions of fin rays and membranes covering fin rays light yellow, with diffuse scattering of yellow to brown chromatophores covering entire fin membranes on both sides of fins. Entire dorsal and anal fins with scattered streaks separating fins into darker and lighter areas. Basal margins on blind sides of these fin rays and associated fin membranes light-yellow to light-brown.

Pigmentation of recently preserved specimens. Similar to that of freshly caught fishes; pigmentation of specimens preserved for decades usually faded, except dermal spots at bases of anterior dorsal-fin rays, pepper-dots on the isthmus, and the bluish-black peritoneum still clearly visible.

Size and sexual maturity. A total of 22 specimens, ranging in size from 35.3–67.5 mm SL, included 12 females, 35.3–67.5 mm SL. Males (n = 10, 47.9–65.5 mm SL) attain similar sizes to those of females. Of the 12 females, three (35.3–53.4 mm SL) are immature showing little elongation of the ovaries, while eight others (54.0–63.0 mm SL) are non-gravid, mature females with elongate ovaries, only one female (67.5 mm SL) was gravid.

Distribution. Symphurus robustus is known from voucher specimens taken on the continental shelf in Tosa Bay, the Pacific side of Japan. ( Fig. 3 ). Based on these specimens, S. robustus is a shallow–water tonguefish, occurring at depths ranging from 45 m to 90 m, with most captures usually occurring between 45 and 64 m. Symphurus robustus is frequently collected on muddy substrata, or on substrata consisting of a mixture of mud and sand.

Etymology. The name robustus is derived from the Latin, in reference to the relatively massive, and much thicker body of this species compared with that of other similar shallow-water tonguefishes.

Comparisons. Of species of shallow-water tonguefishes from the Indo-West Pacific, S. robustus is most similar to the other four nominal species belonging to the high scale count group of the S. microrhynchus species complex, i.e., S. brachycephalus , S. hongae , S. leptosomus , and S. polylepis . Differences between S. robustus and these other species were highlighted above in the Comparisons sections in the species accounts for each of these species, respectively.

Differences between S. robustus and members of the low scale count species group of the S. microrhynchus complex ( S. holothuriae , S. longirostris , and S. microrhynchus ) were discussed above in the Comparisons section in the species accounts for each of these species, respectively.

Symphurus robustus also shares some similarities with S. monostigmus and S. leucochilus , including the same ID pattern (1-2-2-2-2) and overlapping counts for dorsal-fin rays (85–88 vs. 86–92), anal-fin rays (72–76 vs. 73– 80), total vertebrae (46–48 vs. 48–51), and several scale counts. However, S. robustus is readily differentiated from both S. monostigmus and S. leucochilus in having a membranous connection between the ocular-side anterior nostril and lower eye, and S. robustus also possesses a fleshy ridge on the ocular-side lower jaw; both features absent in these other species.

Symphurus robustus differs further from S. monostigmus in having 12 caudal-fin rays and 4 hypurals (vs. 14 caudal-fin rays and 5 hypurals), and in lacking the pigment spot on the abdomen that features so prominently in S. monostigmus . Symphurus robustus also has fewer scales in longitudinal series (72–78) and fewer transverse scales (32–34) compared with that (vs. 92 and 36–38, respectively) found in S. monostigmus . The head of S. robustus is much narrower (HW/HL= 1.06–1.20) compared with that (HW/HL= 1.38–1.42) of S. monostigmus .

A further difference between S. robustus and S. leucochilus is the number of longitudinal scales, which are more numerous in S. robustus (78–88) compared with values (75–83) for this feature found in S. leucochilus .

Figures

FIGURE 3. Geographic distribution of Symphurus microrhynchus, S. holothuriae, and five new species of Indo-West Pacific shallow-water tonguefishes based on specimens examined in this study. Symbols may represent more than one locality and/or more than a single collection from each locality.

FIGURE 11. Symphurus robustus n. sp., holotype, BSKU 45132, male, 60.0 mm SL, Off Kochi, Japan.A. Ocular side pigmentation of preserved specimen. B. Blind-side pigmentation of holotype. C. Symphurus robustus n. sp., paratype, BSKU 44097, male, 50.0 mm SL, Off Kochi, Japan, Ocular-side pigmentation of fresh specimen (Provided by Dr. H. Endo). D. Symphurus robustus n. sp., paratype, BSKU 44098, male, 63.7 mm SL, Off Kochi, Japan, Ocular-side pigmentation of fresh specimen (Provided by Dr. H. Endo). Scale equals 10 mm.