Symphurus polylepis, 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 : 36-39

Symphurus polylepis n. sp.

(English name: Small-scale tonguefish)

( Figs. 3 , 10 ; Tables 1–5, 10)

Symphurus microrhynchus (not Weber 1913). (?) Kailola, 1971: 118 (specimen from Papua New Guinea, not examined in present study; compared with S. holothuriae and S. trifasciatus ).

New Guinea species. Munroe 1992: 362, 374, 401 (ID patterns of five specimens; unidentified species, likely undescribed, distinct from S. microrhynchus and S. holothuriae ).

Symphurus microrhynchus (not Weber): Munroe & Marsh, 1997: 191 (misidentified as S. microrhynchus ).

Holotype: USNM 245733 , male, 49.5 mm SL, North of Tovel , Papua New Guinea, bottom trawl, 23 m, 10º10.22’S, 148º06’ E, “Alpha Helix” CR. Moro, 13 Jun 1979.

Paratypes: Four specimens (26.7–34.8 mm SL): USNM 236607 , 2 specimens, immature female and male, 31.0– 34.8 mm SL, Creek Mouth , West side of Daru, Papua New Guinea, 0–10 m, 10 Oct 1975 . USNM 265183 , 2 males, 26.7–32.8 mm SL, Daru Wharf , East side of Daru, Papua New Guinea, 0–10 m, T. Roberts, 10 Oct 1975 .

Diagnosis. Symphurus polylepis 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; 46–48 total vertebrae; 4 hypurals; 84–87 dorsal-fin rays; 68–74 anal-fin rays; 88–94 longitudinal scale rows; 32–34 transverse scale rows; and 17–19 scale rows on head posterior to lower orbit. Fleshy ridge well developed on posterior part of ocular-side lower jaw; and with fleshy membrane covering both eyes; anterior margin of upper eye usually slightly in advance of anterior margin of lower eye; with fleshy flap continuous between ocular-side anterior nostril and anterior region of lower eye; upper head lobe usually wider than lower head lobe; head length moderately long (HL= 21.9–23.8% of SL) with relatively large postorbital length (POL= 15.7–16.6% of SL, 69.3–73.3% of HL); preanal length relatively short (PAL= 23.5–24.6% of SL); snout short (SNL= 16.0–18.3% of HL, SNL/ED= 1.44–1.86), rounded to obliquely blunt anteriorly; head length usually shorter than head width (HW/HL= 1.02–1.14); dorsal-fin origin in posterior position at, or slightly posterior to, vertical through posterior margin of upper eye; moderately long predorsal length (PDL= 5.7–7.1% of SL; 24.4–31.4% of HL); ocular side uniformly yellow to light-brown; blind side uniformly white; both sides with obvious dermal spots on bases of anteriormost dorsal- and anal-fin rays; peritoneum bluish-black.

Description. Symphurus polylepis ( Fig. 10 ) is a tonguefish species, known only from five specimens, the largest of which is 49.5 mm SL. Meristic characters summarized in Tables 2–5. Predominant ID pattern 1–2–2–2–2 (5/ 5 specimens). Caudal-fin rays 12. Dorsal-fin rays 84–87. Anal-fin rays 68–74. Pelvic-fin rays 4. Total vertebrae 46–48; abdominal vertebrae 9 (3 + 6). Hypurals 4. Longitudinal scale rows 88–94. Scale rows on head posterior to lower orbit 17–19. Transverse scale rows 32–34.

Proportions of morphometric features presented in Table 10. 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 slightly shorter than body depth. Head moderately short and wide; head width longer than head length (HW/HL= 1.02–1.14, Mean= 1.09). Upper head lobe wider than lower head lobe (UHL/LHL= 1.04–1.24, Mean= 1.15); much 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 relatively short, slightly rounded to obliquely blunt anteriorly, its length slightly greater than eye diameter (SNL/ED= 1.44–1.86, Mean=1.59). Dermal papillae present and well developed on blind side of snout and chin. Ocular-side anterior nostril tubular and short, usually when depressed posteriorly 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, moderately 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 much longer than snout length; posterior margin of upper jaw usually extending to point between verticals through anterior margin of lower eye and midpoint of lower eye. Ocular-side lower jaw with well-developed fleshy ridge on its posterior half. Cheek depth narrow, slightly shorter than snout length. Eyes moderate in size (ED= 9.9–11.3% of HL), oval, contiguous, with membrane covering both eyes; fleshy membrane of skin connecting lower eye to anterior nostril. Eyes usually unequal in position with anterior margin of upper eye usually in advance of anterior margin of lower eye. Pupillary operculum absent. Dorsal-fin origin located between verticals at posterior margin of pupil and posterior margin of upper 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, usually reaching base of third to fifth anal-fin ray. Posteriormost pelvic-fin ray connected to anal fin by delicate membrane. Caudal fin relatively long, with several (usually less than four) 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 seven rows of well-developed teeth.

Pigmentation. Only known from preserved and faded specimens examined in this study ( Fig. 10 ). Pattern of body pigmentation generally similar for both sexes and for all sizes. Background body pigmentation of ocular side generally light-yellow to light-brown, usually with 4–9 distinct, narrow (covering about 2–4 scales), complete or incomplete, brown, crossbands; crossbands not continued onto dorsal and anal fins; some specimens with crossbands faded and indistinct, or with uniformly brown pigmentation without crossbands; pigmentation of body region overlying pterygiophores of dorsal and anal fins usually the same as background pigmentation. Dark pigment along vertebral axis absent on all specimens. No melanophores in dermis on body region overlying pterygiophores. External surface of abdominal area usually brown to bluish-black. Background pigmentation of ocular side of head generally similar to that on body, except for dark region of dermal melanophores concentrated behind eyes. Ocular side of snout light-yellow, obvious dermal spots at bases of anterior dorsal-fin rays and also on the isthmus. Outer surface of ocular-side opercle yellow to light-brown, margin of opercle yellow to light-brown, with same background pigmentation as that on body and head. Inner surface of ocular-side opercle and isthmus with small light reddish dots; ocular-side lips and chin region uniformly yellow to brown; margins of lips with small, dark chromatophores. Ocular-side anterior nostril light-yellow to brown. Upper aspects of eyes and eye sockets blackish; pupils bluish-black, usually lighter in pigmentation than sockets. Blind side generally white to light-yellow with bluish-black peritoneum. No median longitudinal row of darkly pigmented melanophores along vertebral axis at all sizes. Outer surface of blind-side opercle white to light-yellow similar to background pigmentation on body. 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 membrane on both sides of fins. Entire dorsal and anal fins with regularly scattered streaks separating darker and lighter areas of fins. Basal margins of fin rays on blind side and associated fin membranes, light-yellow to light-brown.

Size and Sexual maturity. Five specimens range in size from 25.1–49.5 mm SL. Four are males (25.1–49.5 mm SL), while the fifth specimen is an immature female (34.8 mm SL) with little elongation of the ovaries. Since none of the five specimens are adult females, i.e., either gravid or with elongate ovaries, we are unable to determine size or size at maturity offor adult females s, or size at maturity of females, forof this species.

Distribution. Symphurus polylepis is only known from specimens collected at two inshore sites offshore at Daru, and one offshore site north of Tovel, Papua New Guinea ( Fig. 3 ). Based on information associated with these limited specimens, S. polylepis is a shallow-water species of tonguefish, occurring at depths ranging from 0–23 m, with most captures usually occurring between 0 and 10 m. More accurate information about geographic distribution, bathymetric distribution and substrata inhabited is needed to better understand the ecology, distribution and life history of this species.

Etymology. The name polylepis is derived from the Greek, poly meaning many, and lepis, meaning scale, in reference to the greater number of longitudinal scale rows compared with that of similar species of shallow-water tonguefishes.

Remarks. Kailola (1971) tentatively identified a specimen taken off Papua, New Guinea, as S. microrhynchus based on its meristic features (87 dorsal-fin rays; 76 anal-fin rays; 86 longitudinal scales), and by its distinct pigmentation. This specimen was not examined in the present study. However, meristic values for this specimen are identical, or nearly so, to those of S. polylepis (dorsal-fin rays 84–87; anal-fin rays 68–74; and longitudinal scales 88–94). Based on similarities in meristic characters and capture location, we tentatively identify this specimen as S. polylepis .

In his survey of ID patterns of species of Symphurus, Munroe (1992) examined five specimens of an unidentified species of Symphurus from New Guinea. He considered this unidentified species distinct from S. microrhynchus and S. holothuriae and treated this as probably an undescribed species. Later, Munroe & Marsh (1997) re-examined these specimens and incorrectly re-identified them as S. microrhynchus based on their similarities in meristic features to that species.

Comparisons. Of IWP shallow-water tonguefishes, S. polylepis is most similar to four other nominal species ( S. brachycephalus , S. robustus n. sp., S. hongae , and S. leptosomus ) that together with S. polylepis belong to the high scale count group of species of the S. microrhynchus species complex. Except for S. robustus n. sp., differences between S. polylepis and these other species were highlighted in the Comparisons sections appearing in the accounts above for each of these species.

Symphurus polylepis is easily distinguished from S. robustus n. sp. by differences in their pigmentation. Symphurus polylepis lacks pepper-dots and dermal melanophores at bases of the dorsal- and anal-fin rays (vs. well-developed pepper-dots and dermal melanophores at bases of dorsal- and anal-fin rays present in S. robustus n. sp.). In its meristic features, S. polylepis differs from S. robustus n. sp. in having more longitudinal scales (88–94 vs. 78–88 in S. robustus n. sp.).

Differences between S. polylepis and members of the S. microrhynchus species complex with lower scale counts ( S. holothuriae , S. longirostris , and S. microrhynchus ) were discussed in the Comparisons sections above for each of these species, respectively.

Symphurus polylepis has the same ID pattern (1–2–2–2–2) and counts for some meristic features that overlap those found in the South African species, S. monostigmus , and in the northwestern Pacific Ocean shallow-water species, S. leucochilus . Symphurus polylepis differs from both in possessing a fleshy membranous connection between the ocular-side anterior nostril and the eye (vs. absent in these others), and S. polylepis has a fleshy ridge on the ocular-side lower jaw, which is also absent in both S. monostigmus and S. leucochilus .

Symphurus polylepis is readily differentiated from S. monostigmus in having 12 caudal-fin rays and 4 hypurals (vs. 14 caudal-fin rays and 5 hypurals in S. monostigmus ). Symphurus polylepis also has a narrower head (HW/HL= 1.02–1.14) compared with that (HW/HL= 1.38–1.42) found in S. monostigmus . Symphurus polylepis is further differentiated from S. monostigmus by differences in their ocular-side pigmentation (ocular-side background pigmentation generally light-yellow to light-brown, usually with 4–9 distinct, narrow (covering about 2–4 scales), complete or incomplete, brown, crossbands and no freckles or conspicuous spot on the abdomen in S. polylepis vs. whitish background overlain with freckles and with conspicuous pigmented spot on the abdomen in S. monostigmus ).

Symphurus polylepis differs further from S. leucochilus in numbers of dorsal-fin rays (84–87 in S. polylepis vs. 89–92 in S. leucochilus ), anal-fin rays (68–74 vs. 76–80), total vertebrae (46–48 vs. 49–51), longitudinal scales (88–94 vs. 75–83), and S. polylepis also has more head scales (17–19 vs. 15–17) than does 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 10. Symphurus polylepis n. sp., holotype, USNM 245733, male, 49.5 mm SL, Off North of Tovel, Papua New Guinea. A. Ocular-side pigmentation of preserved specimen. B. Blind-side pigmentation of same specimen. Scale equals 10 mm.