Leiognathus robustus, SPARKS & DUNLAP, 2004

SPARKS, JOHN S. & DUNLAP, PAUL V., 2004, A Clade of Non-Sexually Dimorphic Ponyfishes (Teleostei: Perciformes: Leiognathidae): Phylogeny, Taxonomy, and Description of a New Species, American Museum Novitates 3459 (1), pp. 1-22 : 6-9

Leiognathus robustus , new species

Figures 3–6

HOLOTYPE: UMMZ 242144, 183.4 mm SL, adult male; Singapore: fish market; H.H. Ng, 16 July 2001.

PARATYPES: AMNH 233607, 1 ex., 167.9 mm SL, male; Singapore: fish market; H.H. Ng, July 2002 ; UMMZ 240362, 1 ex., 165.5 mm SL, female; Singapore: fish market; H.H. Ng, July 2002 .

DIAGNOSIS: Leiognathus robustus is distinguished from the only other species of leiognathid known to possess a non­sexually dimorphic LOS, L. equulus , by the absence of an occipital hump (vs. pronounced hump), the presence of a mildly sloping predorsal profile (vs. strongly curved, creating the image of an arched back), frontal and lateral ethmoid ossifications that project anterodorsally and extend well anterior of the orbit to form a distinct preorbital protuberance (vs. slight bulge above orbit), and a nuchal spine that is not exposed in lateral view (vs. exposed and projecting, particularly distally).

DESCRIPTION: Selected proportional measurements and meristic data are presented in table 2. A deep­bodied and robust Leiognathus , which grows to a large size (> 180 mm SL) (figs. 3, 4). Body laterally compressed. No pronounced supraoccipital (= predorsal) hump (fig. 5A). Lateral snout outline mildly concave. Strong preorbital protuberance due to hypertrophy and protrusion of frontal and lateral ethmoid ossifications (fig. 6A). Predorsal head profile mostly straight to mildly curved; back not strongly arched. Nuchal spine not protruding, and distal tip not exposed (figs. 3A, 4, 5A). Nuchal spine with distinct median keel. Two short and stout postnasal spines present on lateral ethmoid, located posterior to nasal foramina and just rostrodorsal of orbit. Postnasal spines followed posteriorly by well­developed supraorbital ridges; ridges converge posteriorly. Dorsal and ventral profiles about evenly curved. Dorsal­fin origin about midway between pelvic­fin and anal­fin origins. Analfin origin at about level of vertical through seventh dorsal­fin spine. Eye large. Caudal peduncle slender and shallow. Mouth small and terminal in position, directed slightly downward when protruded. Caudal margin of maxilla exposed, reaching to level of vertical through anterior margin of orbit. Anterior nasal pore round, posterior foramen crescent­shaped, partially encircling anterior pore. Lower preopercular margin weakly serrate. Vertebral count: 9 precaudal + 14 caudal = 23. Neural and hemal spines of vertebral centrum PU4 expanded and bladelike (fig. 6A). Fifteen or 16 stout and triangular outer ceratobranchial gill rakers arrayed along lower limb (= ceratobranchial one) of first gill arch.

Fins: Dorsal fin with VIII spines and 16 branched rays. First dorsal­fin spine greatly reduced in length, yet relatively robust. Second through fourth dorsal­fin spines elongate and robust, second spine longest. Third and fourth dorsal­fin spines serrate along anterior margin, ‘‘lock’’ into groove on preceding spine when erect. Dorsal­fin spines five through eight feeble, shorter than second through fourth spines. Anal fin with III spines and 14 branched rays. First anal­fin spine very short. Second and third anal­fin spines robust and elongate, second spine longest. Third anal­fin spine serrate on anterior margin, ‘‘locks’’ into groove on posterior margin of second spine when erect. Spinous dorsal and anal fins with asquamate basal sheath, creating furrow into which fins may retract. Pelvic fins short, not reaching first anal spine when adducted. Eight upper and seven lower branched caudal­fin rays. Nineteen total pectoral­fin rays.

Dentition: Multiple rows of small, closely set, elongate and moderately recurved, villiform teeth present in both upper and lower jaws. Four to five closely set rows anteriorly and one to two rows posteriorly in upper jaw. Three to four rows anteriorly and one to two rows posteriorly in lower jaw. Lips fleshy and rugose.

Squamation: Body scales small and cycloid. Head and opercular region naked. Breast naked, asquamate region extending to pectoral­fin base. Lateral line arched and complete. Pored scales in lateral line number 60–65. Pores well developed. Pelvic axillary scale well developed and elongate. All fins asquamate.

PIGMENTATION IN PRESERVATION: Body ground coloration gray to grayish­blue dorsal of midline, and pale yellow, white, or golden ventral of midline. Iridescent golden patches present to varying degree along lateral midline. Cheek and opercular region iridescent silvery to golden. Head above orbit and nape

TABLE 2 Morphometric and Meristic Data of Leiognathus robustus , new species, and L. equulus Measurements (mm) are percentage standard length (SL) or percentage head length (HL), unless noted otherwise. H indicates count corresponding to holotype.

grayish to grayish­brown. Snout dusky to blackish; appears spotty due to concentrated melanophores. Nasal region and lips pale yellow. Gular region with iridescent silvery or golden patches. Chest and belly white or pale gray. Caudal peduncle and base of caudal fin iridescent silvery or golden. Dorsal, anal, pectoral, and pelvic fins whitish to yellow. Dorsal fin with black pigment distally. Pectoral­fin axil blackish due to concentration of melanophores, surrounded by large iridescent silver patch. Pectoral­fin base silvery. Caudal fin yellowish to light brown, dorsal and ventral rays with black pigment, especially proximal to base. Caudal fin with prominent black terminal band. Pelvic axillary scale and body along anal­fin base silvery or golden. Pores of lateral line scales edged dorsally and ventrally with melanophores.

LIGHT­ ORGAN SYSTEM (LOS) (fig. 3): Sexual dimorphism of the light organ and associated structures is not detected. The light organ of males is not enlarged compared to the similarly sized conspecific female and does not exhibit any apparent shape dimorphism. The light organ is a comparatively simple, dorsoventrally compressed, doughnut­shaped structure surrounding the esophagus (fig. 3B). Neither the dorsal nor ventral lobes of males are hypertrophied compared to the conspecific female examined. Likewise, associated structures of the LOS (e.g., clearing of the gasbladder lining, modifications of the integument) do not exhibit any sexually dimorphic attributes. As in all other leiognathids, the posteroventral margin of the gasbladder chamber and the small, thin anteroventral patch separating the light organ from the gasbladder are transparent. This ‘window’ is sparsely ‘peppered’ with iridescent silvery and bluish chromatophores. No lateral clearing of the silvery gasbladder lining is evident (fig. 3B). Externally sexually dimorphic features of the LOS (i.e., male specific transparent patches or stripes in the opercular region or on the flanks) are absent (figs. 3A, 4).

DISTRIBUTION: Known at this time only from market specimens purchased in Singapore. Given that the Singapore fleet fishes throughout much of the Indo­Pacific basin, we are unable to report the collection locality of the type series. The overall similarity of L. robustus to L. equulus , a common and widespread species, or to other large leiognathid species such as L. dussumieri or L. fasciatus , suggest that L. robustus may be easily misidentified, and therefore may traditionally have been overlooked in collections.

ETYMOLOGY: Named in reference to the robust nature and large size of the species compared to all congeners except L. equulus , its sister taxon, and L. fasciatus . The specific epithet, robustus , is used as an adjective.

Figures

Fig. 3. Leiognathus robustus, holotype, UMMZ 242144, 183.4 mm SL, adult male; Singapore. A. External anatomy, illustrating general pigmentation pattern, and absence of transparent flank or opercular

Fig. 4. Leiognathus robustus, holotype, UMMZ 242144, adult male, 183.4 mm SL, Singapore.

Fig. 5. Left lateral view of head of: (A) Leiognathus robustus, holotype, UMMZ 242144, adult male, 183.4 mm SL; (B) Leiognathus equulus, UMMZ 238805, adult male, 173.4 mm SL. Arrow indicates nuchal spine.

Fig. 6. Comparative radiographs of similarly sized (A) Leiognathus robustus, holotype, UMMZ 242144, adult male, 183.4 mm SL, and (B) Leiognathus equulus, UMMZ 238805, adult male, 173.4 mm SL.