Description of a New Species of Ponyfish (Teleostei: Leiognathidae: Equulitini: Photolateralis) from the Gulf of Oman

Copyright © American Museum of Natural History 2019 ISSN 0003-0082 AMERICAN MUSEUM NOVITATES Number 3929, 14 pp. June 19, 2019 Description of a New Species of Ponyfish (Teleostei: Leiognathidae: Equulitini: Photolateralis) from the Gulf of Oman JOHN S. SPARKS1 AND PROSANTA CHAKRABARTY2 ABSTRACT A new species belonging to the leiognathid genus Photolateralis, collected from the coastal waters of Oman, is described herein. Photolateralis is unique among leiognathid genera in possessing a species-specific translucent midlateral flank stripe that may be comprised of either multiple independent translucent windows (P. stercorarius, P. moretoniensis, and the new species) or a continuous translucent lateral band (P. antongil). Photolateralis polyfenestrus, new species, is distinguished from congeners by the presence of a short, composite midlateral stripe comprised of three small, rounded translucent windows (vs. numerous windows in both P. stercorarius and P. moretoniensis, or a continuous translucent stripe in P. antongil), and that is confined to the midflank (vs. extending a majority of the length of the flank in congeners). The new species is further distinguished from both P. moretoniensis and P. antongil by a shallower body, and from both P. stercorarius and P. moretoniensis by a pigmentation pattern above the lateral midline comprised primarily of larger rounded blotches (vs. smaller sinuous lines and markings comprising a vermiculated pattern). Photolateralis polyfenestrus is characterized by a lower jaw that is deep and convex in lateral view (vs. mostly straight in congeners, excluding P. antongil), and that forms an angle of between 60°–70° to horizontal (vs. less than 45° in congeners, excluding P. antongil). The only other species of Photolateralis reported from the Western Indian Ocean is P. antongil, to date only known from the coastal waters of Madagascar, whereas both P. stercorarius and P. moretoniensis have ranges restricted to the western Pacific and extending into the eastern Indian Ocean. 1 Department of Ichthyology, Division of Vertebrate Zoology, American Museum of Natural History. 2 Museum of Natural Science (Fish Section), Department of Biological Sciences, Louisiana State University. 2 AMERICAN MUSEUM NOVITATES NO. 3929 INTRODUCTION The genus Photolateralis was recently described by Sparks and Chakrabarty (2015) to encompass members of Leiognathidae that are characterized by a species-specific translucent midlateral flank stripe. Photolateralis currently comprises three species, P. stercorarius (Evermann and Seale, 1907), P. moretoniensis (Ogilby, 1912), and P. antongil (Sparks, 2006), not including the new species described herein. This characteristic flank stripe may either be comprised of multiple independent translucent windows (P. stercorarius, P. moretoniensis, and the new species) or is a continuous translucent lateral band (P. antongil), through which bacterially mediated luminescence is presumably transmitted from the light organ via clearing of the silvery lateral lining of the gas bladder (Sparks et al., 2005; Sparks, 2006; Sparks and Chakrabarty, 2015). All members of Photolateralis were formerly placed in Equulites (Kimura et al., 2008; Chakrabarty et al., 2011a, 2011b), and Photolateralis shares the presence of translucent lateral flank regions with its sister genus Equulites, although the morphology of these translucent regions differ substantially between the two genera. Photolateralis is recovered as the sister group to Equulites, and together these two genera comprise the tribe Equulitini (Chakrabarty et al., 2011a, 2011b), which is the sister taxon to the tribe Nuchequulini within the subfamily Gazzinae (Chakrabarty and Sparks, 2015). Members of Photolateralis can be distinguished from their sister taxon Equulites, as well as other members of the family, by both external and internal features of their light-organ system. Externally, male members of Equulites are characterized by an expansive and translucent triangular, cornucopia-shaped, or trapezoidal patch on the flank (Sparks and Chakrabarty, 2007: fig. 1), versus a continuous or composite midlateral stripe comprised of multiple independent translucent windows in Photolateralis (Sparks and Chakrabarty, 2015: fig. 3). In Photolateralis, the translucent lateral stripe is either lacking entirely in females, or is considerably less developed (note: only the holotype, a male, is known for the new species). Both Equulites and Photolateralis exhibit lateral clearing (= translucence) of the guanine-lined internal gas bladder surface, and the extent of clearing corresponds to the location of the translucent external patches or stripe. Lateral gas bladder clearing in Equulites, however, is far more extensive, extending the full length of the gas bladder, whereas in Photolateralis clearing is restricted to the posterior region of the gas bladder (see Sparks et al., 2005: figs. 4, 5; Sparks and Chakrabarty, 2015: figs. 2, 4). Male members of Photolateralis exhibit a moderately enlarged donutshaped light organ that extends at most only slightly posteriorly into the gas bladder space, whereas the light organ in male members of Equulites is greatly enlarged, with paired dorsolateral lobes extending posteriorly well into the gas bladder space (less E. leuciscus) (see Sparks and Chakrabarty, 2015: figs. 2, 4). Based on a number of taxonomically comprehensive family-level phylogenetic hypotheses that have been generated in recent years, we now have a better understanding of leiognathid diversity, intrafamilial relationships, and the evolution of their unique light-organ system (Sparks and Dunlap, 2004; Sparks et al., 2005; Chakrabarty et al., 2011a, 2011b). As a result of these phylogenetic studies, extensive fieldwork, and detailed morphological comparisons, several new leiognathid genera and species have recently been described (e.g., see Chakrabarty 2019 SPARKS AND CHAKRABARTY: NEW SPECIES OF PONYFISH 3 and Sparks, 2008; Sparks and Chakrabarty, 2015; Suzuki and Kimura, 2017). In the present study, a new species belonging to Photolateralis is described from material collected in the Gulf of Oman. MATERIALS AND METHODS Morphometric measurements were recorded to the nearest 0.1 mm using dial calipers. Standard length (SL) is used throughout. Vertebral counts exclude the ural centrum (= last half-centrum). The first caudal vertebra is here defined as the first vertebra bearing a definite hemal spine (Hubbs and Lagler, 1949). Vertebral and fin-spine/ray counts were obtained from radiographs. The terminal dorsal-fin and anal-fin rays, which are branched to the base of the fin, are counted as a single element. Morphology of the light-organ system was examined in situ (new species) or in isolation via dissection to permit detailed anatomical comparisons. Sex of the holotype was confirmed via dissection. Osteological and soft tissue features were analyzed using standard film and digital radiographs, high-resolution digital images, MRIs (Chakrabarty et al., 2011a), examination of whole alcohol-preserved specimens, specimens cleared-and-stained (C&S) for bone and cartilage (following the protocol of Taylor and Van Dyke, 1985), and dry skeletal (S) preparations. Specimens examined are listed under Material Examined in appendix 1. Institutional abbreviations are as listed in Leviton et al. (1985) and Sabaj Pérez (2014). RESULTS Systematic Account Photolateralis polyfenestrus, new species Figures 1, 2; table 1 Holotype: AMNH 267152, 66.8 mm SL, male; Sultanate of Oman: Gulf of Oman, Fish Market, 23° 36′ N; 058° 33′ E; Z. Baldwin, July 2008. Diagnosis: Photolateralis polyfenestrus is distinguished from congeners by the presence of a short, composite midlateral stripe comprised of three small, rounded translucent windows that are peppered with chromatophores (vs. numerous windows in both P. stercorarius and P. moretoniensis, or a continuous translucent stripe in P. antongil) and is confined to the midflank (vs. extending most to entire the length of the flank in congeners). The new species is further distinguished from both P. stercorarius and P. moretoniensis by a pigmentation pattern above the lateral midline comprised of larger rounded blotches and markings (vs. smaller sinuous lines and markings forming a vermiculate pattern), and both P. moretoniensis and P. antongil by a shallower body. Photolateralis polyfenestrus exhibits a lower jaw that is deep and convex in lateral view (vs. mostly straight in congeners, less P. antongil), and that forms an angle of between 60°–70° to horizontal (vs. less than 45° in congeners, less P. antongil). The only other species of Photolateralis reported from the western Indian Ocean is P. antongil, to date only known from the coastal waters of Madagascar, and whereas both P. stercorarius and P. moretoni- 4 AMERICAN MUSEUM NOVITATES NO. 3929 ensis have more extensive ranges, nevertheless they are restricted to the western Pacific and extending into the eastern Indian Ocean. Description: Proportional measurements and meristic data presented in table 1 and internal osteological features can be visualized in figure 2. A moderately shallow-bodied and elongate leiognathid. Body laterally compressed. Lateral snout outline straight with a protuberance above upper lip. Mouth small and terminal in position. Premaxilla long and protruding along dorsal margin. Posterior margin of maxilla exposed, reaching to level of vertical through anterior margin of orbit. Lower jaw deep and noticeably convex in lateral view, forming angle of 60°–70° to horizontal. Mild preorbital protuberance due to protrusion of both frontal and lateral ethmoid ossifications. Predorsal head profile weakly sloping and straight. Nuchal spine (exposed rising dorsal aspect of the supraoccipital crest) very slightly protruding and distal tip exposed. Nuchal spine with distinct median keel. Eye large. Anterior nasal pore small and round; posterior foramen much larger and crescent shaped, partially encircling anterior pore. 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 well-developed supraorbital ridges that converge posteriorly. One supraneural present with strong anterior process. Preopercular margin smooth, not serrate, along ventral and ventrocaudal margins. Dorsal and ventral body profiles mildly rounded, with ventral profile more convex than dorsal. Dorsal-fin origin located well posterior to vertical through pelvic-fin origin. Anal-fin origin located at about level of vertical through the last (= 8th) dorsal-fin spine/first dorsal-fin ray. Caudal peduncle slender and shallow. Total vertebral count 23: 10 precaudal + 13 caudal. Neural and hemal spines of vertebral centrum PU4 weakly expanded distally and bladelike. Thirteen elongate and triangular outer gill rakers arrayed along lower limb (= 5th ceratobranchial) of first gill arch. Fins: Dorsal fin with VIII spines and 16 branched rays. First dorsal-fin spine greatly reduced in length and somewhat robust. Second through fourth dorsal-fin spines elongate and robust; second spine longest. Second dorsal-fin spine moderately, but not exceedingly, elongate compared to third and fourth. Third and fourth dorsal-fin spines serrate along anterior margin “lock” into groove on posterior margin of preceding spine when erect (fig. 2). Dorsal-fin spines five through eight feeble, considerably shorter than second through fourth spines. Anal fin with III spines and 14 branched rays. First anal-fin spine very short. Second and third anal-fin spines robust and elongate. Third anal-fin spine serrate on anterior margin “locks” into groove on posterior margin of second spine when erect (fig. 2). Spinous dorsal and anal fins with asquamate basal sheath. Eighteen total pectoral-fin rays. Pelvic fins short, not reaching first anal-fin spine when adducted (i.e., a significant gap present). Eight upper and seven lower branched caudal-fin rays. Dentition: Two distinct rows of extremely closely set, elongate and recurved conical teeth present in both upper and lower jaws. Upper jaw teeth somewhat larger and more recurved than those of lower jaw. Lips fleshy, and teeth embedded. Squamation: Body scales cycloid. Head and opercular region asquamate. Chest fully scaled, except along ventral midline. Scales conspicuous. Squamation extends anteriorly, ventral to 2019 SPARKS AND CHAKRABARTY: NEW SPECIES OF PONYFISH 5 TABLE 1. Morphometric and Meristic Data for Holotype of Photolateralis polyfenestrus. Character Holotype Standard length (mm) 66.8 Percentage of SL Head width (max.) 13.2 Head length 27.7 Body depth 35.9 Caudal peduncle length 5.4 Caudal peduncle width 2.3 Caudal peduncle depth 5.8 Pectoral-fin length 19.5 Predorsal length 41.5 Preanal length 53.4 Prepelvic length 33.1 Percentage of HL Snout length 33 Orbit diameter 34.6 Upper jaw length 22.7 Lower jaw length 58.4 Interorbital width 30.8 Caudal peduncle length/width 2.4 Caudal peduncle length/depth 0.9 Gill rakers (lower limb 1st arch) 13 Vertebrae (precaudal + caudal) 10 + 13 = 23 Dorsal fin VIII 16 Anal fin III 14 opercle, to approximately anterior margin of chest. Lateral line arched and complete, located well dorsal to lateral midline. Pored scales in lateral line highly embedded and difficult to visualize and count. Pores well developed. All fins asquamate, except for caudal fin, which bears several rows of cycloid scales of reduced size, particularly centrally on fin. Pigmentation in Preservative: Body ground coloration olive to light brown above lateral midline, and silvery, guanine covered below midline (fig. 1). Pigmentation pattern above lateral midline characteristically blotchy and mottled, comprised of darker brown roundish blotches and broad lines over olive to light brown background. Blotches variable in size and somewhat closely arranged, particularly rostrodorsally. Body just ventral to lateral midline peppered with melanophores. Opercle, interopercle, and lacrimal iridescent silvery with golden hue. Preopercle, subopercle, and cheek iridescent and silvery. Short, composite, midlateral stripe present, comprised of three oblong dark gray translucent windows studded with chromatophores, and appearing much darker than surrounding region due to concentration of 6 AMERICAN MUSEUM NOVITATES NO. 3929 FIG. 1. Photolateralis polyfenestrus, new species, holotype, AMNH 267152, male, 66.8 mm SL; Sultanate of Oman: Gulf of Oman, Mutrah Fish Market. Note: Specimen has field tag on posterior flank and anteriormost midlateral window is obscured behind pectoral-fin rays in image. melanophores. Stripe located at midflank, beginning about level of terminal adducted pelvic-fin rays. Lips grayish. Lower jaw and gular region grayish. Snout with large black patch above upper lip. Two distinct black blotches present anterior to orbit; dorsal blotch covering anterior portion of postnasal spines on lateral ethmoid. Dorsal and ventral margins of orbit lined in black pigment. Interorbital region and nape grayish anteriorly to grayish-brown posteriorly. Large, oblong dark brown marking posterior to orbit and dorsal to opercle. Chest and belly silvery; silvery along ventral midline. Dorsal and anal fins hyaline to pale yellowish-white, with a slight concentration of black pigment distally on dorsal-fin spines. Base of dorsal fin black; becoming more prominent (i.e., darker) posteriorly. Pectoral and pelvic fins yellowish tan. Caudal peduncle pale tannish yellow with blackish saddle on dorsal margin. Base of caudal fin pale yellow. Caudal fin yellowish to olive proximal to base, becoming translucent to white distally. Membrane of caudal fin with concentration of black pigment, creating series of thin, black radiating lines, particularly near base. Light-Organ System (LOS): In Photolateralis the light-organ system is internally characterized by a moderately enlarged, donut-shaped, and conspicuously spotted light organ in males that extends only slightly posteriorly into the gas bladder. In contrast, in members of Equulites, its sister taxon, the dorsolateral lobes of the light organ in males are greatly enlarged, heavily pigmented, and extend posteriorly well into the gas bladder. Internally, male members of Photolateralis exhibit posterolateral clearing of the silvery gas bladder lining, corresponding in extent to the external translucent lateral stripe or windows on the flank. The light-organ system in the new species is similar to that described for males of other members of Photolateralis (see Sparks, 2006; Sparks and Chakrabarty, 2015). In the new species, lateral clearing of the gas bladder lining corresponds to the three external translucent midlateral windows, the anteriormost window located at about the midpoint of the adducted pectoral-fin rays. Externally, members of Photolateralis are distinguished from all other leiognathids by the presence of a translucent flank stripe, which, depending on the species, may be comprised of either 2019 SPARKS AND CHAKRABARTY: NEW SPECIES OF PONYFISH 7 FIG. 2. Radiograph of Photolateralis polyfenestrus, new species, holotype, AMNH 267152, male, 66.8 mm SL; Sultanate of Oman: Gulf of Oman, Mutrah Fish Market. multiple independent translucent windows (P. stercorarius, P. moretoniensis, and the new species) (figs. 1, 3A–C), or a continuous midlateral band (P. antongil) (fig. 3D). In Photolateralis, the translucent lateral stripe is either lacking entirely in females, or is considerably less well developed. Distribution: Known only from a single specimen acquired at a fish market (23° 36′ N; 058° 33′ E) in northeastern Oman, Sultanate of Oman. The new species is presumably more widespread in the region as well as in the Gulf of Oman. Extensive recent surveying and collecting in the adjacent portion of the Persian (Arabian) Gulf did not result in any additional observations of this species (personal obs.). Etymology: Named in reference to the characteristic translucent midlateral windows, which are rounded and appearing spotlike. The specific epithet, polyfenestrus, is used as an adjective. DISCUSSION AND COMPARISONS As many as 10 leiognathid species have been reported to occur in the coastal waters of Oman (Randall, 1995; Al-Jufaili et al., 2010, Froese and Pauly, 2019). In addition, recent studies have confirmed the occurrence of both E. elongatus (Jayabalan et al., 2010; Jawad et al., 2013), which had previously been reported from Oman, and E. klunzingeri (Jawad et al., 2012), new record, from the coastal waters of Oman, Although both of these species are shallow-bodied, elongate ponyfishes, they are characterized by an expansive translucent triangular or trapezoidal patch on the flank in males (Sparks and Chakrabarty, 2007: fig. 1a, d). The only species Photolateralis polyfenestrus could potentially be misidentified as and confused with (and that has been reported to occur in the region) is the species commonly referred to as Leiognathus oblongus or Equulites oblongus (Valenciennes, 1835) (fig. 4). Note, we use Equulites oblongus for convenience only, as there are no external apomorphic features that can 8 AMERICAN MUSEUM NOVITATES NO. 3929 FIG. 3. Species of Photolateralis illustrating phenotypic variability of translucent midlateral flank stripe characteristic of genus. (A) P. stercorarius, USNM 55906, holotype, 83.8 mm SL, Philippines. (B) P. stercorarius, SIO 96-96, non-type, 98.2 mm SL, Philippines. (C) P. moretoniensis, AMS I.22983001, nontype, 76.9 mm SL, Australia. (D) P. antongil, AMNH 236544, holotype, 75.0 mm SL, Madagascar. 2019 SPARKS AND CHAKRABARTY: NEW SPECIES OF PONYFISH 9 FIG. 4. Equula oblonga, holotype, MNHN A-6754, 61.8 mm SL; Timor, Indonesia. be identified on the holotype to place the species in Equulites. The holotype of E. oblongus is intact, nondissected, and lacking any evidence of translucent flank patch(es) or a stripe that would allow one to place it in the genus Equulites. Based on overall body shape, including lateral profile of the lower jaw and remaining flank pigmentation pattern above the lateral midline in preservation, we believe the holotype of E. oblongus (MNHN A-6754) should actually be placed in Photolateralis. We further note, however, that specimens attributed to E. oblongus (from Oman) are much deeper bodied than the holotype of E. oblongus, exhibit a very different pigmentation pattern on the flank above the lateral midline, and lack the translucent lateral windows or stripe that characterize the new species, and members of Photolateralis in general (compare figs. 1 and 3 with fig. 4; also see Randall, 1995: 193, fig. 486). Based on external morphology, the specimen shown by Randall and identified as E. oblongus (1995: fig. 486) appears to be a female E. leuciscus. Equulites leuciscus is a widespread species in the Indo-West Pacific, with a range reportedly extending from East Africa and Madagascar, to northern Australia and New Caledonia, to Vietnam, Taiwan, and China (personal obs.); Froese and Pauly, 2019), but that has not previously been reported from Oman. The original description of E. oblongus is insufficient for distinguishing this species from other members of Equulitini, despite the holotype (MNHN A-6754) being in relatively good condition (fig. 4). In addition to the translucent lateral flank windows present in the new species, P. polyfenestrus can easily be distinguished from the holotype of E. oblongus by flank pigmentation pattern above the lateral midline (few large, roundish blotches in E. oblongus vs. a more blotchy and variable pattern in the new species, comprised of numerous smaller and more irregular dark, roundish markings), a deeper body, a straight predorsal profile (vs. rounded in E. oblongus), and a much deeper and concave (vs. relatively straight and short in E. oblongus) lateral lower jaw profile (figs. 1–2, 4). All issues of Novitates and Bulletin are available on the web (http://digitallibrary. amnh.org/dspace). 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