Symphurus leptosomus, 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 : 32-36

Symphurus leptosomus n. sp.

(English name: Slender tonguefish)

( Figs. 3 , 9 ; Tables 1–5, 9)

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

Holotype: USNM 379566 , male, 23.6 mm SL, rotenone, Philippines, 13º13.25’N, 120º33.56’E, 15 m, Min Team & M. Santos, 3 Jun 2000.

Diagnosis. Symphurus leptosomus 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 total vertebrae; 4 hypurals, 88 dorsal-fin rays, 72 analfin rays, 76 longitudinal scale rows, 37 transverse scale rows, and 20 scale rows on head posterior to lower orbit; an elongate body, with preanal length much longer than body depth (PAL/BD= 1.09); head moderately long (HL= 23.9% of SL), with head length slightly shorter than head width (HW/HL= 1.02); postorbital length short (POL= 65.5% of HL); upper head lobe larger than lower head lobe; dorsal-fin origin at vertical through midpoint of upper eye; predorsal length moderately long (PDL= 20.4% of HL); snout short (SNL= 16.8% of HL), and rounded anteriorly; upper eye slightly in advance of lower eye; fleshy ridge well-developed on posterior part of ocular-side lower jaw, with fleshy membrane covering both upper and lower eyes, and membranous fleshy flap continuous between ocular-side anterior nostril and lower part of eye; with ocular-side pigmentation uniformly yellow to light-brown with dark-brown irregular speckles and blotches; blind-side pigmentation uniformly white, with well-developed pepper-dots and dermal melanophores at bases of dorsal and anal fins; bases of anteriormost dorsal- and anal-fin rays with obvious dermal spots on both sides; peritoneum bluish-black.

Description. Symphurus leptosomus is likely a dwarf species, known only from a male measuring 23.6 mm SL ( Fig. 9 ). Meristic characters summarized in Tables 2–5. ID pattern 1–2–2–2–2. Caudal-fin rays 12. Dorsal-fin rays 88. Anal-fin rays 72. Pelvic-fin rays 4. Total vertebrae 47; abdominal vertebrae 9 (3 + 6). Hypurals 4. Longitudinal scale rows 76. Scale rows on head posterior to lower orbit 20. Transverse scale rows 37.

Proportions of morphometric features presented in Table 9. Body relatively slender; maximum depth in anterior one-third of body at point equal with vertical at second anal-fin ray, body with gradual taper posterior to midpoint. Preanal length longer than body depth. Head moderately short and wide; head width longer than head length (HW/ HL= 1.02). Upper head lobe wider than lower head lobe (UHL/LHL= 1.20); and 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 anteriorly, but its length much greater than eye diameter (SNL/ED= 1.72). Dermal papillae present, well developed, on blind side of snout and chin. Ocular-side anterior nostril tubular and short, not reaching anterior margin of lower eye when depressed posteriorly. Ocular-side posterior nostril a small, rounded tube located on snout just anterior to interorbital space. Blind-side anterior nostril tubular and moderately long, easily distinguishable from dermal papillae; blindside posterior nostril a shorter and wider, posteriorly directed tube, situated posterior to vertical at posterior margin of jaws. Jaws moderately long and slightly arched; upper jaw length much longer than snout length; posterior margin of upper jaw extending to point equal with vertical through 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 relatively small (ED= 9.7% of HL), oval, contiguous, with membrane covering both eyes, eye membrane connected to anterior nostril by fleshy flap of skin. Upper eye slightly in advance of lower eye. Pupillary operculum absent. Dorsal-fin origin located at vertical through midpoint of upper eye; predorsal length relatively short. 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 fourth 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 rows of sharp, recurved teeth. Blind-side lower jaw with four rows of well-developed teeth.

Pigmentation. Symphurus leptosomus is only known from the preserved holotype ( Fig. 9 ), which has lightbrown, ocular-side background pigmentation covered with irregular, dark-brown speckles and blotches. Speckles and blotches not continued onto dorsal and anal fins. Pigmentation overlying pterygiophore regions of dorsal and anal fins similar to that of background pigmentation elsewhere. A series of larger melanophores overlying vertebral axis. Melanophores in dermis overlying dorsal- and anal-fin pterygiophores well developed. External surface of abdominal area usually brown to bluish-black. Background pigmentation of ocular-side of head generally similar to that on body, with one darker region behind eyes formed by dense patch 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 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 blackish dots; ocularside lips and chin region uniformly yellow to brown, margins of lips pigmented with small dark chromatophores. Ocular-side anterior nostril light-yellow to brown. Upper aspects of eyes and eye sockets blackish; pupils bluishblack, lighter in pigmentation than sockets. Blind side generally white to light-yellow with pepper-dots present on pterygiophore regions overlying dorsal- and anal-fins. Peritoneum bluish-black. Median longitudinal row of darkly pigmented melanophores clearly visible along vertebral axis. Outer surface of blind-side opercle white to lightyellow similar to background pigmentation on blind side of body. Inner surface of blind-side opercle more darkly pigmented than outer surface. Fin rays of dorsal, anal, and pelvic fins uniformly light-brown; basal regions of fin rays and membranes covering fin rays yellow, with diffuse scattering of yellow to brown chromatophores covering entire fin membranes on both sides of fins. Entire dorsal and anal fins with pattern of darker streaks separated by lighter areas. Basal margins of fin rays on blind side, and associated fin membranes, light-yellow to light-brown.

Size and Sexual maturity. Symphurus leptosomus is only known from the holotype, a male measuring 23.6 mm SL. Additional specimens are needed to further investigate and determine maximum size and size at maturity for this species.

Distribution. Symphurus leptosomus is only known from a specimen collected at an offshore site off western Mindoro, Philippines ( Fig. 3 ). Based on information associated with this specimen, S. leptosomus is a shallow-water species of tonguefish, occurring at depths of ca. 15 m. Further investigations are needed to better understand intraspecific variation, ecology, abundance and life history of this species.

Etymology. The name leptosomus is derived from the Greek, lepto meaning slender, and somus, meaning body, in reference to its relatively slender, elongate body compared with that of other similar species of shallow-water tonguefishes.

Comparisons. Symphurus leptosomus is a member of the high scale count species group of the S. microrhynchus species complex. Among the five members of this group, S. leptosomus is most similar to S. hongae and S. robustus n. sp. in that these three species have pepper-dots and dermal melanophores at the bases of the dorsal and anal fins. Other differences between S. leptosomus and S. hongae were highlighted in the Comparisons section of the species account for S. hongae above.

Compared with S. robustus n. sp., S. leptosomus has higher counts for head scales (20 vs. 16–18 in S. robustus n. sp.) and transverse scales (37 vs. 31–34 in S. robustus n. sp.). In its morphometric features, S. leptosomus differs from S. robustus n. sp. in having a relatively narrower body (BD= 24.6% of SL vs. 25.5–28.3% of SL in S. robustus n. sp.), a preanal length longer than body depth (PAL/BD= 1.08 vs. 0.77–0.96 in S. robustus n. sp.), and S. leptosomus has a relatively longer head (HL= 23.9% of SL vs. 19.1–21.8% of SL in S. robustus n. sp.). These species also differ in some aspects of their pigmentation. For example, S. leptosomus features irregular dark-brown speckles and blotches covering its ocular side (vs. ocular side uniformly light-brown, usually with 5–7 crossbands, in S. robustus n. sp.).

Comparisons between S. leptosomus and S. brachycephalus were highlighted in the Comparisons section of the species account above for S. brachycephalus . Symphurus leptosomus is easily distinguished from S. polylepis n. sp. in having well-developed pepper-dots and dermal melanophores at the bases of the dorsal and anal fins (vs. no pepper-dots or dermal melanophores at bases of the dorsal and anal fins in S. polylepis n. sp.). In meristic features, S. leptosomus differs from S. polylepis n. sp. in having more transverse scales (37 vs. 32–34 in S. polylepis n. sp.), and fewer longitudinal scales (76 vs. 88–94 in S. polylepis n. sp.).

Differences between S. leptosomus and members of the species group of the S. microrhynchus species complex characterized by having lower scale counts ( S. holothuriae , S. longirostris , and S. microrhynchus ) were discussed and highlighted above in the Comparisons section in each of the accounts for these species.

Symphurus leptosomus has the same ID pattern (1–2–2–2–2) and has similar or overlapping counts for dorsal-fin rays (88 vs. 86–92), anal-fin rays (72 vs. 73–80), and total vertebrae (47 vs. 48–51) as those found in S. monostigmus and S. leucochilus . However, S. leptosomus 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 also in having a fleshy ridge on the ocular-side lower jaw; both features that are absent in these other species. Symphurus leptosomus also has its head length nearly equal to its width (HW/HL= 1.02) versus head width greater than head length (HW/HL= 1.07–1.42) in these other two species,.

Symphurus leptosomus differs further from S. monostigmus in having 12 (vs. 14) caudal-fin rays and 4 hypurals (vs. 5 hypurals), and in lacking the pigment spot on the abdomen that features so prominently in S. monostigmus .

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 9. Symphurus leptosomus n. sp., holotype, USNM 379566, male, 23.6 mm SL, Off the Philippines.A. Ocular-sidepigmentation of preserved specimen. B. Blind-side pigmentation of same specimen. Scale equals 10 mm.