Symphurus holothuriae Chabanaud, 1948

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 : 17-20

Symphurus holothuriae Chabanaud, 1948

( Figs. 3–4 ; Tables 1–6)

Symphurus holothuriae Chabanaud, 1948: 510 (Holothuria Bank, northwestern Australia. Holotype: BMNH 1892.1.14.34; compared with S. trifasciatus ). Chabanaud 1955b: 45 (comparisons with S. microrhynchus ; pigmentation features; probably synonym of S. microrhynchus ). Munroe 1992: 376 (ID pattern; discussion about taxonomic status; comment on melanophores at bases of dorsal and anal fins; similar to S. microrhynchus ). Lee et al. 2017: 71 (compared with S. longirostris ).

Symphurus holothuriae (not Chabanaud). Nielsen 1961: 226 (2 specimens of S. schultzi misidentified as S. holothuriae ). Munroe 1992: 372 (re-identified 2 specimens of S. schultzi that were misidentified as S. holothuriae ). Munroe & Marsh 1997: 195 (discussed 2 specimens of S. schultzi misidentified as S. holothuriae ).

Symphurus microrhynchus (not Weber). Munroe & Marsh 1997: 191 (synonym of S. microrhynchus ).

Holotype: BMNH 1892.1 .14.34, 32.3 mm SL, male, off Holothuria Bank , northwestern Australia, 14 Jan 1892.

Diagnosis. Symphurus holothuriae is distinguished from all congeners by the combination of: a 1–2–3–2–2 ID pattern; 12 caudal-fin rays; 9 (3 + 6) abdominal vertebrae; 46 total vertebrae; 4 hypurals; 84 dorsal-fin rays; 70 anal-fin rays; 60 longitudinal scale rows; 25 transverse scale rows; 16 scale rows on head posterior to lower orbit; body elongate (BD 25.7% of SL); preanal length long (PAL 27.6% of SL); upper head lobe equal in length to lower head lobe; head long (HL 24.0% of SL), head length longer than head width (HW/HL= 0.97); postorbital length long (POL of 75.9% HL); snout short (SNL 14.3% of HL, SNL/ED= 1.45) and slightly blunt anteriorly; dorsal-fin origin at vertical through posterior margin of upper eye; predorsal length short (PDL= 19.7% of HL); eyes unequal in position with anterior margin of upper eye noticeably in advance of anterior margin of lower eye; well-developed fleshy ridge on posterior part of ocular-side lower jaw; body pigmentation yellowish-green on both sides.

Description. Symphurus holothuriae ( Fig. 4 ) is likely a dwarf species and is known only from a single, male specimen of 32.3 mm SL. Meristic characters are summarized in Tables 2–5. ID pattern 1–2–3–2–2. Caudal-fin rays 12. Dorsal-fin rays 84. Anal-fin rays 70. Pelvic-fin rays 4. Total vertebrae 46; abdominal vertebrae 9 (3+6). Hypurals 4. Longitudinal scale rows 60. Scale rows on head posterior to lower orbit 16. Transverse scale rows 25.

Proportions of morphometric features are presented in Table 6. Body elongate; maximum depth in middle of body, at point about equal to vertical at 10 th anal-fin ray; body with gradual taper posterior to midpoint. Preanal length longer than body depth. Head moderately long and narrow; head width shorter than head length (HW/HL= 0.97). Upper head lobe equal to width of lower head lobe (UHL/LHL= 1.00), and much shorter than postorbital length. Lower lobe of ocular-side opercle wider than upper lobe; posterior margin of lower lobe projecting slightly beyond posterior margin of upper opercular lobe. Snout short, slightly blunt anteriorly, its length slightly greater than eye diameter (SNL/ED= 1.45). Dermal papillae present and 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 relatively short, easily distinguishable from dermal papillae; blind-side posterior nostril a shorter and wider, posteriorly directed tube situated posterior to vertical at posterior margin of jaws. Jaws long and slightly arched; upper jaw length slightly longer than snout length; posterior margin of upper jaw extending to vertical through posterior margin of lower eye. Ocular-side lower jaw with well-developed fleshy ridge on its posterior portion. Cheek depth relatively wide, slightly greater than snout length. Eyes small, oval, unequal in position with anterior margin of upper eye greatly in advance of anterior margin of lower eye. Pupillary operculum absent. Dorsal-fin origin located at vertical through posterior margin of upper eye; predorsal length relatively short. Anteriormost dorsal-fin rays obviously shorter than more posterior dorsal-fin rays. Scales absent on both sides of dorsal- and anal-fin rays. Pelvic fin long; longest pelvic-fin ray, when extended posteriorly, usually reaching base of sixth anal-fin ray. Posteriormost pelvic-fin ray connected to anal fin by delicate membrane. Caudal fin broken; uncertain if ctenoid scale rows present on base of fin or not. 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. Pigmentation of live or freshly collected S. holothuriae unknown. Background pigmentation of both sides of preserved holotype ( Fig. 4 ) a faded, uniform yellowish-green. Upper aspects of eyes and eye sockets bluish-black; pupils yellowish-green.

In the original description, Chabanaud (1948) described the preserved holotype as having a uniformly light reddish-yellow ocular side with paler fins. Later, Chabanaud (1955b) noted that the holotype of S. holothuriae lacked any evidence of transverse banding and it also lacked darkly pigmented melanophores along bases of the dorsal- and anal-fin rays. Munroe & Marsh (1997) reported that when they examined the holotype, the specimen was mostly faded, but, in contrast to the statement of Chabanaud (1955b), a few dermal melanophores were evident on the bases of some anterior dorsal-fin rays.

Distribution. Symphurus holothuriae is known only from a single specimen collected on Holothuria Bank, northwestern Australia ( Fig. 3 ).

Remarks. In the original description, Chabanaud (1948) did not compare S. holothuriae with S. microrhynchus , only with S. trifasciatus , an Indian Ocean deepwater species featuring similar meristic features. Later ( Chabanaud 1955b), did compare S. holothuriae with S. microrhynchus noting that S. holothuriae lacked the transverse bands that were present on S. microrhynchus and that it also lacked the series of darkly pigmented melanophores along bases of the dorsal- and anal-fin rays, which are present in S. microrhynchus . Chabanaud (1955b) did not consider these differences significant because he stated that S. holothuriae was very similar to, and probably a synonym of, S. microrhynchus .

The next paper dealing with S. holothuriae was that of Munroe (1992) in his survey of ID patterns among species of Symphurus . Munroe noted that S. holothuriae was only one of three species ( S. undatus and S. hondoensis representing the others) featuring a 1–2–3–2–2 ID pattern. Sometimes, species characterized by the 1–2–2–2–2 ID pattern have variant specimens that have a 1–2–3–2–2 ID pattern. Since S. holothuriae is known only from the holotype, it cannot be determined whether the predominant ID pattern for this species is 1–2–3–2–2, or if the pattern present in the holotype represents a variant pattern for this species. More specimens of S. holothuriae are needed to determine the predominant ID pattern for this species.

Munroe (1992) also noted that S. holothuriae was otherwise morphologically similar to three other poorly known Indo-Pacific species ( S. microrhynchus , S. trifasciatus , and S. luzonensis ). Except for differences in ID patterns (1–2–3–2– 2 in S. holothuriae vs. 1–2–2–2– 2 in these others), S. holothuriae has comparable caudal-, dorsal-, and anal-fin ray counts and vertebral counts, to those found in these others.

In their redescription of S. microrhynchus, Munroe & Marsh (1997) considered S. holothuriae to be a junior subjective synonym of S. microrhynchus . They noted that the holotype of S. holothuriae has meristic and morphometric features that generally agree with those of the holotype of S. microrhynchus , their opercle shapes are similar, and S. holothuriae has a few dermal melanophores present at the bases of the anteriormost dorsal-fin rays, which are also present in S. microrhynchus . Munroe & Marsh (1997) also noted some differences between the holotypes of these two species including those in ID pattern and the lower vertebral count of S. holothuriae compared with that of S. microrhynchus , but did not think these differences were sufficient to distinguish these as different species.

More recent evidence, based on morphology ( Lee et al. 2014; 2017), indicates that S. holothuriae is a shallowwater species belonging to the low scale count group within the S. microrhynchus species complex. In addition to S. holothuriae , this species group also includes S. longirostris and S. microrhynchus . Further examination of additional specimens is needed to gain better understanding of intraspecific variation, ecology, abundance, and life history attributes for this species.

Comparisons. Among shallow-water species of Symphurus , S. holothuriae is most similar to S. microrhynchus and S. longirostris , the other members of the low scale count group of species in the S. microrhynchus species complex. These species share similar general body shapes, and have overlapping counts of dorsal-, anal-, and caudal-fin rays, longitudinal scales, and transverse scales ( Tables 4–5). Differences between S. holothuriae and S. microrhynchus were highlighted above in the Remarks and Comparisons sections for S. microrhynchus .

Symphurus holothuriae differs from S. longirostris in having more scale rows on the head posterior to the lower eye (16 vs. 11–14 in S. longirostris ) and in several morphometric features ( Table 6). Symphurus holothuriae has a longer and wider head (vs. head shorter and narrower in S. longirostris ), a shorter SNL (vs. longer), smaller ratio of SNL/ED (larger ratio in S. longirostris ), shorter lower jaw (vs. longer), and relatively longer POL. Symphurus holothuriae has a more anterior insertion of the 1 st dorsal-fin ray than does S. longirostris , which results in this species having a shorter PDL (18.1% of HL) compared with that of S. longirostris (PDL> 23.8% of HL). The lower head lobe is also larger than the upper head lobe (UHL/LHL= 0.78), whereas in S. longirostris the lower head lobe is smaller than the upper head lobe (UHL/LHL= 1.01–1.20). Other differences between S. holothuriae and S. longirostris were discussed in Lee et al. (2017).

Symphurus holothuriae differs from the group of five species in the S. microrhynchus species complex featuring high scale counts ( S. brachycephalus n. sp., S. hongae n. sp., S. leptosomus n. sp., S. polylepis n. sp., and S. robustus n. sp.) by its fewer longitudinal (64 vs. 72–94) and transverse scales (25 vs. 26–37 in these others). And, in S. holothuriae , head width is narrower than the corresponding head length, whereas, in the five species with high scale counts, their heads are wider than long (HW/HL= 0.97 in S. holothuriae vs. HW/HL ranging from 1.02–1.20 for these other species).

Symphurus holothuriae has overlapping, or nearly overlapping, counts for dorsal-fin rays (87 vs. 86–92), and anal-fin rays (70 vs. 73–80) as those found in S. monostigmus and S. leucochilus . However, S. holothuriae is readily differentiated from both S. monostigmus and S. leucochilus in having a different ID pattern (1–2–3–2–2 vs. 1–2–2– 2– 2 in these others) and fewer total vertebrae (46 vs. 48–51). Symphurus holothuriae has a membranous connection between the ocular-side anterior nostril and the lower eye, and this species also has a fleshy ridge present on the ocular-side lower jaw; both features are absent in these other species. Additionally, S. holothuriae has fewer longitudinal (60 vs. 75–92) and transverse scales (25 vs. 32–38) than is found in these other species. In S. holothuriae , the head length is nearly equal to its width (HW/HL= 0.97) versus head width greater than head length (HW/HL= 1.07–1.42) in these other two species. Symphurus holothuriae differs further from S. monostigmus in having 12 (vs. 14) caudal-fin rays and 4 (vs. 5) hypurals, and S. holothuriae lacks 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 4. Symphurus holothuriae, holotype, BMNH 1892.1.14.34, male, 32.2 mm SL, off Holothuria Bank, northwestern Australia. A. Ocular-side pigmentation of preserved specimen. B. Blind-side pigmentation of same specimen. Scale equals 10 mm.