Symphurus monostigmus Munroe, 2006

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 : 44-47

Symphurus monostigmus Munroe, 2006

(English name: Spotbelly tonguefish)

( Figs. 12 ; Tables 1–5, 12)

Symphurus monostigmus Munroe, 2006: 230 , Fig. 1 ( South Africa, KwaZulu-Natal, off Gypsy Hill, 65– 110 m. Holotype: SA- IAB 39811). Munroe & Hashimoto, 2008: 53 (compared with S. thermophilus ). Lee et al. 2009: 347 (compared with S. megasomus ). Munroe et al. 2011: 64 (compared with S. maculopinnis ). Lee et al. 2014: 580 (listed in comparisons). Lee et al. 2017: 72 (listed in introduction).

Holotype: SAIAB 39811 , male, 48.8 mm SL, off Gypsy Hill , KwaZulu-Natal, South Africa, Western Indian Ocean, 110 m, 27º45.20’ S, 32º39.80’ E, R. N. Kilburn, aboard the R / V Meiring Naude, 8 Jun 1988.

Paratype: USNM 383435 ), male, 54.6 mm SL, off Gypsy Hill , KwaZulu-Natal, South Africa, Western Indian Ocean, 65–70 m, 27º47.40’ S, 32º38.90’ E , R. N. Kilburn, aboard the R / V Meiring Naude, 8 Jun 1988 .

Diagnosis. Symphurus monostigmus is distinguished from all congeners by the combination of: a 1–2–2–2–2 ID pattern; 14 caudal-fin rays; 9 (3 + 6) abdominal vertebrae; 48 total vertebrae; 5 hypurals; 86 dorsal-fin rays; 73–74 anal-fin rays; 92 longitudinal scale rows; 36–38 transverse scale rows; and 18–19 scale rows on the head posterior to lower orbit; body deep (BD= 28.8–32.4% of HL); preanal length short (PAL= 21.3–25.5% of SL); upper head lobe much wider than lower head lobe; head moderately short (HL= 18.0–20.2% of SL), with head length much shorter than head width (HW/HL= 1.38–1.42); postorbital length long (POL= 75.8–79.4% of HL); snout short (SNL= 13.6–14.8% of HL; SNL/ED= 1.08–1.25), rounded to obliquely blunt anteriorly; dorsal-fin origin at vertical at anterior margin of upper eye; predorsal length short (PDL= 16.4–19.3% of HL); eyes equal in position (anterior margin of upper eye equal with anterior margin of lower eye), or slightly subequal (with anterior margin of upper eye anterior to that of lower eye); without fleshy ridge on ocular-side lower jaw; ocular-side pigmentation yellowish-white with numerous freckles along bases of dorsal- and anal-fin rays; blind-side pigmentation uniformly white; peritoneum bluish-black.

Description (from Munroe 2006). Known from two specimens, the holotype ( Fig. 12a ) measuring 48.8 mm SL, and a paratype ( Fig. 12b ) of 54.6 mm SL. Meristic data for paratype in parentheses when different from that of holotype. Meristic information summarized in Tables 2–5. ID pattern 1–2–2–2–2. Caudal-fin rays 14. Dorsal-fin rays 86. Anal-fin rays 74 (73). Pelvic-fin rays 4. Total vertebrae 48; abdominal vertebrae 9 (3 + 6). Hypurals 5. Longitudinal scale rows about 92 (many scales missing, count made from blind side; paratype missing too many scales to estimate). Scale rows on head posterior to lower orbit 18 (19).

Proportions of morphometric features for holotype and paratype are presented in Table 12. Body moderately elongate, tapering gradually anteriorly and posteriorly; greatest body depth in anterior one-third of body, slightly posterior to anus. Preanal length less than or slightly greater than body depth. Head width greater than head length (HW/HL= 1.39 for holotype, 1.42 for paratype). Postorbital head length shorter than width of upper head lobe. Snout short, bluntly rounded to squarish, its length noticeably longer than eye diameter. Dermal papillae present on blind side of snout and chin. Ocular-side anterior nostril tubular, elongate, when depressed posteriorly reaching, or nearly reaching, anterior margin of lower eye. Ocular-side posterior nostril a small round opening situated in anterior interorbital space. Blind-side anterior nostril a short, round tube, readily distinguishable from dermal papillae. Blind-side posterior nostril a small round opening. Eyes moderate in size (ED= 10.9–13.6% of HL), round; equal or slightly subequal in position, with anterior margin of lower eye slightly posterior to that of upper eye. Eyes nearly contiguous for most of their lengths, without ctenoid scales in extremely narrow interorbital space, and without small scales on upper aspects of eyes. Pupillary operculum absent. Pupil small, pupil diameter/eye diameter 32% (28% in paratype). Upper-jaw length greater than snout length, posterior margin reaching point between verticals through anterior margin of pupil and midpoint of lower eye. Upper head lobe noticeably wider than lower head lobe. Posterior margin of opercle with obvious indentation. Upper opercular lobe much wider than lower opercular lobe, which extends more posteriorly than upper opercular lobe. Dorsal-fin origin located at point between verticals through anterior margin of pupil and midpoint of upper eye. Both sides of dorsal- and anal-fin rays without scales. Caudal fin elongate, with several rows of small ctenoid scales on basal one-third to one-half of blind and ocular sides of fin.

Teeth well developed on all jaws; blind-side dentary with three to four rows of teeth, blind-side premaxilla with two to three rows; ocular-side dentary with two rows of teeth anteriorly and one row posteriorly, ocular-side premaxilla with single row covering about one-half of anterior jaw.

Pigmentation in alcohol. Ocular side generally yellowish-white and freckled with numerous, darker, reddishbrown markings especially well developed on posterior halves of scales (best viewed under magnification), with traces of two or three dorsal and two ventral, darker, reddish-brown blotches along dorsal and ventral margins on posterior half of body (blotches extending slightly medially), and with a prominent, irregular, conspicuous brown spot (about seven scales long and six scales wide) on anteroventral portion of abdominal cavity just behind gill opening. Abdominal spot extending slightly beyond ventral midline onto blind side of paratype. Head pigmentation generally similar to that of body, but lighter overall. Outer and inner surfaces of opercles on both sides without conspicuous pigmentation. Isthmus unpigmented. Lips without dark pigmentation. Anterior nostril yellowish-white. Blind side of body uniformly yellowish-white. Peritoneum unpigmented anteriorly, spotted in mid-region, black posteriorly; darker posterior region visible externally through body wall on both sides of body. Middle and posterior dorsal and anal fins with faint traces of series of pigmented rays (two to three successive fin rays) alternating with larger series of unpigmented fin rays. Pelvic fin unpigmented. Distal two-thirds of caudal fin unpigmented, proximal one-third with faint, light-brown pigment on bases of fin rays.

Remarks. Symphurus monostigmus is a poorly known species, with only two specimens, collected on the inner continental shelf at 65–110 m, off KwaZulu-Natal, South Africa, known for the species ( Munroe 2006). Further investigation is needed to gain better understanding of intraspecific variation, genetic information, ecology, abundance and life history of this species.

Comparisons. Symphurus monostigmus has some meristic features that overlap those of members of the S. microrhynchus species complex and also overlap with those of S. leucochilus . Symphurus monostigmus differs from all members of the S. microrhynchus species complex and also from S. leucochilus because it is the only known IWP shallow-water tonguefish with five hypurals and 14 caudal-fin rays. All other IWP shallow-water congeners feature four hypurals and 12 caudal-fin rays. Symphurus monostigmus also differs from these others in its unique ocularside pigmentation, which consists of a uniformly yellowish-white background overlain by freckles ( Munroe 2006), and with a prominent spot on the anterior abdomen. This pigmentation pattern easily separates this species from all other IWP shallow-water tonguefishes.

Figures

FIGURE 1. Diagnostic pigmentation features on blind sides of Indo-West Pacific shallow-water species of Symphurus. (A) Example of pepper-dots and dermal spots represented by S. hongae, ASIZP0072360, male, 48.0 mm SL, Dong-Gang, SW Taiwan, 04 Jul 2007. (B) Example of an unpigmented blind side represented by S. longirostris, ASIZP0072352, female (mature), 57.3 mm SL, off Kochi, Japan, 04 Apr 1994. (C) Example of median melanophores along vertebral axis as represented by S. leucochilus, holotype, USNM 408271, mature female, 58.7 mm SL, Da-Shi fish market, northeastern Taiwan, 24 Aug 2011. (D) Example of species without median series of melanophores on vertebral axis represented by S. brachycephalus, ASIZP0072364, female (mature), 49.4 mm SL, off Nan Trang, Vietnam, 19 Apr 2009.

FIGURE 12. Symphurus monostigmus, holotype, SAIAB 39811, male, 48.8 mm SL, Off Gypsy Hill, KwaZulu-Natal, South Africa, Western Indian Ocean. A. Ocular-side pigmentation of holotype. B. Blind-side pigmentation of holotype. C. Symphurus monostigmus, paratype USNM 383435, male, 54.6 mm SL, Off Gypsy Hill, KwaZulu-Natal, South Africa, Western Indian Ocean, Ocular-side pigmentation. D. Blind-side pigmentation of paratype. Scale equals 10 mm.