Review of Brazilian jawfishes of the genus Opistognathus with descriptions of two new species (Teleostei, Opistognathidae)

Abstract A new species of jawfish, Opistognathusthionyisp. n., is described from the Vitória-Trindade Chain and Fernando de Noronha Archipelago off Brazil, a disjunct distribution of ca. 1,800 km. Opistognathusthionyi and its allopatric Caribbean sister-species, Opistognathusmaxillosus, both have a wide, fan-like upper margin of the subopercular flap and mostly over-lapping meristic data. The new species differs from O.maxillosus in having the darkest spot on the spinous dorsal fin, when present, between spines 2–5, versus always present between spines 6–9, the buccal area surrounding the esophageal opening pale versus very dark and fewer oblique scale rows in longitudinal series (45–52 vs. 69–85). A second new species, Opistognathusvicinussp. n., known from Brazil’s mainland, has completely over-lapping meristic values with its allopatric Caribbean sister-species O.whitehursti, but differs in lacking vomerine teeth and a supramaxilla and retaining the juvenile color pattern of the latter species in adults. Diagnoses, photographs, an identification key, and distributional maps are given for all Brazilian species of Opistognathus. Molecular phylogenetic analysis of partial cytochrome c oxidase subunit-I sequences indicates that specimens of the two allopatric pairs, O.thionyi – O.maxillosus and O.vicinus – O.whitehursti, form reciprocally monophyletic groups that differ from each other on average by 9 to 11%, with less than 1% average pair-wise genetic distance within-species. Similar patterns of phylogenetic structure were observed between reciprocally monophyletic (predominately allopatric) groups within nominal species of Opistognathusaurifrons, suggesting the possibility of at least two additional undescribed species from the Brazilian Province.

Median fin-ray counts, and characters associated with the vertebral column were usually taken from radiographs. The last two elements in the dorsal and anal fins have their bases in close approximation ("split to base" condition) and were counted as one ray in accord with the general practice of most authors, although the ultimate element has a separate rudimentary pterygiophore or stay. Pectoral-fin ray counts are reported for one side only and include the uppermost rudimentary ray. Caudal-fin ray counts separated by a plus indicate rays associated with the dorsal and then the ventral hypural plate. Vertebral counts are presented as a formula: precaudal + caudal. The lateral-line terminus refers to the base of the posteriomost segmented dorsal-fin ray below which the lateral line ends. The number of oblique body scale rows is only an approximation due to the irregular size and arrangement of individual scale rows. Included in this count are all anteroventrally aligned scale rows in a longitudinal series from above the tip of the opercular flap to the base of the caudal fin (counts of posteroventrally aligned scale rows will result in lower values). The gill raker at the junction of the upper and lower limbs of the first gill arch is included in the lower-limb count; care was taken not to overlook rakers (often very small) at the ends of the gill arch. Counts of gill rakers were usually made only on the right side of specimens. English common names of species, if available, are those of Page et al. (2013).
Specimen sizes in material examined are given as mm SL (standard length) rounded to the nearest 0.1 mm, with number of specimens and size range given in parentheses. Measurements of paratypes indicated by an asterisk were compared with those of the holotypes. Cleared and stained specimens are indicated as "C&S". All measurements were made with needle-point digital calipers and recorded to the nearest 0.1 mm. Measurements of paratypes indicated by an asterisk were compared with holotypes of the new species. Head length is the distance from the middle of the upper lip to the posterodorsal tip of the opercular flap. Postorbital-jaw length is a straight-line measurement from the posterior orbital margin at its junction with the rigid sphenotic bone to a vertical from the posterior end of the upper jaw. Postorbital-jaw ratio is the postorbital jaw length divided by the orbit diameter. Orbit diameter is a diagonal (posterodorsal to anteroventral) measurement of the bony orbit; the posterodorsal point of origin is the rigid sphenotic margin. Body depth is a vertical measurement from the origin of the anal fin. Caudal-peduncle depth is a vertical measurement from the narrowest part of the caudal peduncle. In the color pattern descriptions, stripes refer to markings aligned with the longitudinal axis of the body and bands or bars refer to markings aligned with the vertical axis of the body.
We sequenced a segment of the mitochondrial gene cytochrome c oxidase subunit-I (COI) for 22 samples of Opistognathus, including one specimen of O. whitehursti from St. Croix and three of O. vicinus from Brazil, eight specimens of O. thionyi and eight specimens of O. aff. aurifrons, and one specimen each of O. lonchurus and O. brasiliensis. Whole genomic DNA was extracted using a Qiagen DNEasy Blood and Tissue kit per manufacturers' protocols. Primers for PCR and sequencing reactions were COH6 and COL6 (Shubart et al. 2007) or GobyL6468 and Go-byH7696 (Thacker 2003). Sequences were aligned with several other opistognathid sequences from GenBank and BOLD (Barcode of Life Database, www.boldsystems. org), plus a sequence from Lonchopisthus micrognathus (Poey, 1860) as an outgroup, for a total of 103 sequences. Sequences were assembled and aligned in Geneious v.10.0.9. The best fitting substitution model was chosen using PartitionFinder (Lanfear et al. 2016). Phylogenetic analyses were conducted using maximum likelihood and Bayesian methods in RAxML version 8 (Stamatakis 2014) and MrBayes ver. 3.2.6 (Ronquist et al. 2012), respectively. A distance matrix was created using mean between-group pairwise genetic distances (Table 2); and a haplotype network was created using Haploviewer (Salzburger et al. 2011). GenBank or BOLD accession numbers are listed in the Appendix.      broad, fan-like flap; vomer with 1 tooth; buccal area surrounding esophageal opening pale; body with 45-52 oblique body scale rows in longitudinal series; vertebrae 10+18; spinous dorsal fin with black blotch, when present, between spines 2-5. Body with five poorly defined irregular bands and sides sometimes with diagonal rows of pale spots smaller than eye diameter; when present, black blotch in spinous dorsal fin between spines 2-5; buccal area surrounding esophageal opening pale. This species is also easily distinguished from congeners by divergence in the mitochondrial gene COI, as specimens form a monophyletic group that differs from its closest relative (O. maxillosus) by an average of 9% (654 bp analyzed). Description. Morphometric data are given in Table 3 for the holotype and specimens indicated above by an asterisk; other comparative features are presented in Table 1. Where counts differ, those of the holotype are given first, followed in parentheses by those of the paratypes. Dorsal fin XI,[15][16]. Anal fin III,usually 15). . Vertebrae: 10+18, last pleural rib on vertebra 10, epineurals 13-15. Supraneurals absent. Caudal fin: procurrent rays 5+5 (4-6+4-5); segmented rays 8+8, middle 12 branched, total elements 26 (24-26); hypural 5 absent. Gill rakers (number not increasing with increase in SL in adults) 9+19 (8-11+17-20=25-31).

Key to Brazilian Opistognathus
Scales absent from head, nape, pectoral-fin base and breast; belly completely scaled, and sides fully scaled except for area above lateral line anteriorly. Body with 48 (45-52) oblique scale rows in longitudinal series. Lateral-line terminus below verticals between segmented dorsal-fin ray 3 (3-5). Anterior lateral-line pores relatively numerous and arranged in branched series along lateral-line tubes, all of which are embedded in skin. Mandibulo-preopercular pore positions all consisting of multiple pore series, except first two mandibular pore positions occupied by simple pores. Infraorbital pore positions consisting of multiple series that extend onto cheeks. Nape nearly to completely covered by sensory pores except for V-shaped naked area immediately in front of dorsal-fin origin ( Figure 4A). Anterior nostril positioned closer to posterior nostril than to dorsal margin of upper lip, and adults with a rounded cirrus that usually reaches anterior margin of orbit when depressed; height of cirrus 2.0-3.0 times maximum diameter of posterior nostril. Dorsal fin moderately low anteriorly, with posterior rays slightly longer; profile relatively uniform without noticeable change in fin height at junction of spinous and segmented rays. Dorsal-fin spines stiff and straight with pungent tips and in larger specimens the skin covered tips usually with pale, slightly swollen fleshy tabs. Segmented dorsal-and anal-fin rays all typically branched distally. Outermost segmented pelvic-fin ray not tightly bound to adjacent ray and interradial membrane strongly incised distally; tip of depressed pelvic fin in front of anal-fin origin. Upper margin of subopercle consisting of a broad, truncated flap ( Figure 4A) and dorsalmost spine of opercle not noticeably elongate; posterior margin of preopercle distinct, with a welldeveloped groove dorsally. No papillae on inner surface of lips. Fifth cranial nerve passes over A1β section of adductor mandibulae muscle.
Upper jaw not sexually dimorphic, extending 0.45 (0.3-0.6) eye diameters behind orbit in specimens 32.5-53.5 mm SL; posterior end of maxilla rigid and truncate, without a thin flexible lamina; supramaxilla absent. Coronoid (ascending) process of articular slightly tilted backward and somewhat club-shaped with anterodorsal end bluntly pointed and posteroventral end bluntly rounded ( Figure 5A). Premaxilla anteriorly with an outer row of stout teeth and an inner row of smaller, backward slanting teeth, some nearly horizontal; laterally teeth uniserial and becoming progressively smaller and more closely spaced. Dentary anteriorly with an outer row of stout teeth and an inner row of smaller, backward slanting teeth; laterally teeth uniserial and smaller but not progressively so. Vomer with 1 large tooth. Infraorbital bones tubular, with numerous openings for sensory canals; third infraorbital with a wide suborbital shelf. Postcleithra consisting of two well separated bones; dorsal postcleithrum an irregular elongate oval, narrowest ventrally, ventral postcleithrum rod-shaped with pointed ends.
Color in life (Figures 1, 2). Body coloration chestnut brown to dark brown with five very irregular and poor defined dark bands that extend onto base of dorsal fin; head sometimes with pale speckles on posterior half; upper jaw with a wide white band near posterior end; eyes reddish brown sometimes with narrow pale radiating bands; lips with alternating dark and pale bands; branchiostegal membranes dark, especially in mature males; dorsal fin light yellow sometimes with diagonal rows of pale spots and a black blotch, when present, between spines 2-5; anal fin with small pale spots; pelvic fins dark; pectoral fins speckled and a large white spot on pectoral-fin base; caudal fin with pair of pale basicaudal spots and fin rays with prominent black speckles or narrow bands. (Figure 3). As above except with white, brown, and black markings. Inner margin of maxilla posteriorly and adjacent membranes with dusky blotch. Buccal area surrounding esophageal opening pale.

Preserved color
Comparisons. The Caribbean allopatric Opistognathus maxillosus Poey, 1860 shares with O. thionyi the same subopercle shape but in addition to having more longitudinal body scale rows (69-85 vs. 45-52), the dark spot in the dorsal fin is always between spines 6-9 (vs. when present between spines 2-5), and the buccal area immediately surrounding the esophageal opening very dark (vs. pale). An updated description of Opistognathus maxillosus is given in Smith-Vaniz (1997). The only other species of Opistognathus with a broad, fan-like subopercle are the eastern Pacific O. galapagensis Allen & Robertson, 1991 and O. fossoris Bussing & Lavenberg, 2003. In addition to other characters discussed by Bussing and Lavenberg (2003), both species differ from O. thionyi most notably in having the posterior end of maxilla ending as thin, flexible lamina (vs. end of maxilla rigid), more body longitudinal scale rows, 83-105 (vs. 45-52), most of nape immediately in front of dorsal-fin origin without cephalic pores  (vs. almost completely covered with pores), and in having very different color patterns. Comparison of the six species of Opistognathus known from the Brazilian Province is given in Table 1.
Etymology. The specific name honors our colleague and dear friend Thiony Simon (1985Simon ( -2016, who passed away during preparation of this article. He collected most of the type material of the new species and dedicated his life to study and conservation of Brazilian reef ecosystems. Distribution, habitat, and natural history. Opistognathus thionyi is known only from three oceanic sites, Trindade Island, Dogaressa Seamount, and Fernando de Noronha Archipelago (Figure 6), and is an endemic species of the Brazilian Province (sensu Briggs andBowen 2012 andPinheiro et al. 2018). This species is possibly broadly distributed along the coast on the outer shelf, an area that is virtually unsampled. It has been recorded from 10-65 m, and found solitarily, always in small constructed burrows on sandy rubble bottoms (Figure 7). It feeds on small benthic organisms that live near the bottom (e.g., small shrimps).
Conservation. The conservation status of Opistognathus thionyi (cited as Opistognathus maxillosus Poey, 1860 -unpublished data) has been assessed by the Ministério do Meio Ambiente/Instituto Chico Mendes de Conservação da Biodiversidade (MMA/ICMBio -Brazil) and listed as Least Concern. However, anthropogenic activities on oceanic marine ecosystems (i.e., seamount mining, fisheries, marine traffic, tourism, and human occupation of the islands), and the inadequate protection from these impacts currently provided by new Brazilian marine protected areas in the Vitória-Trindade Seamounts Chain (see Brasil 2018;Giglio et al. 2018;Magris and Pressey 2018), could threat the existence of Thiony's jawfish in that part of its range in the near future.  Diagnosis. A species of Opistognathus with the following combination of characters: anterior nostril a short tube with simple cirrus on posterior rim; maxilla rigid, not produced as a thin flexible lamina posteriorly; supramaxilla absent; subopercle without a broad, fan-like flap; vomer without teeth; body with 43-47 oblique body scale rows in longitudinal series; vertebrae 10+17; sides with two rows of pale spots, each approximately diameter of eye. Body with six vertically irregular, evenly spaced bands, widest on mid-side, and two rows of six pale spots, each spot approximately diameter of eye; buccal area surrounding esophageal opening pale. This species is also easily distinguished from congeners by divergence in the mitochondrial gene COI, as specimens form a monophyletic group that differs from its closest relative (O. whitehursti) by an average of 11% (654 bp analyzed).
Scales absent from head, nape, pectoral-fin base and breast; belly completely scaled, and sides fully scaled except for area above lateral line anteriorly. Body with 46 (43-47) oblique scale rows in longitudinal series. Lateral-line terminus below verticals between segmented dorsal-fin ray 1 (2-3). Anterior lateral-line pores relatively numerous and arranged in branched series along lateral-line tubes, all of which are embedded in skin. Mandibulo-preopercular pore positions all consisting of multiple pore series, except first two mandibular pore positions occupied by simple pores. Infraorbital pore positions consisting of multiple series that extend onto cheeks. Nape nearly to completely covered by sensory pores except for V-shaped naked area immediately in front of dorsal-fin origin ( Figure 4B).
Anterior nostril positioned closer to posterior nostril than to dorsal margin of upper lip, and adults with a slender cirrus that reaches anterior margin of orbit when depressed; height of cirrus 2.0 times maximum diameter of posterior nostril. Dorsal fin moderately low anteriorly, with posterior rays slightly longer; profile relatively uniform without noticeable change in fin height at junction of spinous and segmented rays. Dorsal-fin spines stiff and straight and in larger specimens the skin covered tips usually with pale, slightly swollen fleshy tabs. Segmented dorsal-and anal-fin rays all typically branched distally. Outermost segmented pelvic-fin ray not tightly bound to adjacent ray and interradial membrane strongly incised distally; tip of depressed pelvic fin in front of anal-fin origin. Upper margin of subopercle oval-shaped without a broad, truncated flap ( Figure 4B) and dorsalmost spine of opercle moderately elongate; posterior margin of preopercle distinct, with a well-developed groove dorsally. No papillae on inner surface of lips. Fifth cranial nerve passes over A1β section of adductor mandibulae muscle.
Upper jaw not sexually dimorphic, extending 0.76 (0.62-0.88) eye diameters behind orbit in specimens 36.0-47.4 mm SL; posterior end of maxilla rigid and truncate, without a thin flexible lamina; supramaxilla absent. Premaxilla with a single row of teeth, largest anteriorly becoming smaller and more closely spaced posteriorly, except in mature males posteriormost three or four teeth stouter and more strongly hooked than adjacent teeth. Dentary anteriorly with two rows of teeth, innermost smaller and slanted backwards; laterally teeth uniserial and larger than anterior teeth, posterior teeth of males larger and more strongly hooked than others. Vomer without teeth. Infraorbital bones tubular, with numerous openings for sensory canals; third infraorbital with a wide suborbital shelf. Postcleithra closely attached; dorsal postcleithrum an irregular elongate oval, narrowest ventrally where it overlaps head of ventral postcleithrum; ventral postcleithrum club-shaped, broadest dorsally and with a pointed ventral end.
Color in life (Figure 8). Background color of head and body brownish to reddish brown. Body with six vertically irregular and evenly spaced dark bands, widest on midside, that extend onto base of dorsal fin; two rows of six pale spots on sides, one along dorsal-fin base and the other along anal-fin base, each spot approximately diameter of eye; upper jaw with a wide dark band behind which is a white band at posterior end; the eyes are red; the lips with dark and pale bands; branchiostegal membranes dark; dorsal fin with dark stripe, widest anteriorly, along middle of fin, and a dark blue blotch between the second and fourth spine; pectoral fins are translucent; pelvic fins pale blue to dark or entirely pale; caudal fin with pair basicaudal spots bordered posteriorly by dark continuous band and remainder of fin vertical rows of dark spots or narrow bands.
Preserved color (Figure 9). Body with dark bands and large pale spots as above; other makings various shades of brown. Inner margin of maxilla posteriorly and adjacent membranes with brownish blotch, best developed in males. Buccal area surrounding esophageal opening pale.
Comparisons. Genetic differences (see discussion in "Phylogenetic relationships of western Atlantic Opistognathus"), suggested that Opistognathus vicinus and the Caribbean O. whitehursti could be separate species despite their very similar appearance, including meristic values and sexually dimorphic premaxillary teeth (see Smith-Vaniz 1997: fig. 33). Initially we considered both species to be only "genovariants" sensu Victor ( Figure 11) and the spinous dorsal-fin spot is often absent. As noted by Böhlke and Chaplin (1968: 486) for Bahamas fish, "The spot on the spinous dorsal fin is … blue in color in young, frequently   missing or poorly defined in adults." Thus, the combined differences in COI, adult coloration, and the lack of a supramaxilla and vomerine teeth support the recognition of O. vicinus as a distinct species. Comparison of the six species of Opistognathus known from the Brazilian Province is given in Table 1.

Etymology. From the Latin vicinus (near, neighboring), referring to the allopatric distribution and sister-species phylogenetic relationship of the new species and the Caribbean Opistognathus whitehursti.
Distribution and Habitat. A Brazilian endemic ( Figure 6), known from Ceará to Espírito Santo State but absent from oceanic islands. Common in coastal regions, in depths of 10-25 meters, associated with gravel-sand bottoms, near coral reefs and rocky areas. Feeds on small benthic organisms near the bottom (e.g., small shrimps, crabs, and isopods).
Conservation. The conservation status of this species [cited as Opistognathus whitehursti (Longley 1927   ible, usually curved distally, and tips without pale, slightly swollen tabs; dorsal fin XI, 16 with all soft rays weakly branched distally; anal fin II, 15-16; body with 59-75 oblique scale rows in longitudinal series; vertebrae 10+18; supraneurals 2; gill rakers 9-11+23-24=33-36; spinous dorsal fin with black spot encircled by a very narrow white ring between spines 4-7 and dorsum with 5 or 6 dusky bands that extend onto base of dorsal fin; pelvic fins uniformly dark; underside of upper jaw and adjacent membranes in adults with two elongate dark stripes (males) or one smaller stripe (females) (Smith-Vaniz 1997, Figure 9c). Material examined. 5 specimens (107.5-129 mm SL), including the holotype, cited in Smith-Vaniz (1997)  Distribution, habitat, and natural history. A Brazilian endemic (Figure 6), known from Espírito Santo to São Paulo State, but absent from oceanic islands. A rare species only known from the type series collected in São Paulo's coastal waters (trawled in 50-69 m) and two specimens from Guarapari Islands, Espírito Santo. Occurs in depths of 15-69 meters, associated with gravel and sand or silt and sand bottoms, near coral reefs and rocky areas.
Remarks. In the diagnosis and description of Opistognathus brasiliensis, Smith-Vaniz (1997) stated, in part, "buccal pigmentation consisting of a dark area widely surrounding esophageal opening …" versus area around esophageal opening pale in O. cuvierii. This reported distinction is no longer valid because in a recently examined female specimen of Opistognathus brasiliensis (CIUFES 1459) the area around the esophageal opening is pale. Both species have black areas in front of each pharyngeal tooth patch that are separated by a pale median area.

Abbreviated description.
A species of Opistognathus with the following combination of characters: anterior nostril a short tube with simple cirrus on posterior rim; adults with posterior end of maxilla ending as thin, flexible lamina (slightly elongate in mature females and very elongate in males); supramaxilla present; subopercle without a broad, fan-like flap; most of nape without sensory pores; dorsal-fin spines thin, flexible, usually curved distally, and tips without pale, slightly swollen tabs; dorsal fin XI, 16, with all soft rays weakly branched distally; anal fin II, 16; body with 60-72 oblique scale rows in longitudinal series; vertebrae 10+19; supraneurals 1 or 2; gill rakers 9-11+20-23=30-35; spinous dorsal fin with an ocellus between spines 3-7, otherwise dorsal fin with rows of pale spots and dorsum without 5 or 6 dusky bands that extend onto base of dorsal fin; pelvic fins uniformly dark; caudal fin dark with two  pale bands; underside of upper jaw and adjacent membranes in adults with two dark blotches, the innermost one poorly developed (males) (Smith-Vaniz 1997: fig. 9d), or these blotches absent (females); buccal pigmentation consisting of a dark blotch on either side of esophageal opening widely separated by pale median area that continues between upper pharyngeal tooth patches (Smith-Vaniz 1997: fig. 13c). Material examined. 5 specimens (80.5-11.5 mm SL), including the holotype, cited in Smith-Vaniz (1997).
Distribution, habitat, and natural history. A Brazilian endemic (Figure 6), known from Bahia to São Paulo but absent from oceanic islands. Distributed in coastal regions, in depths between 1-35 meters, associated with gravel and sand or silt and sand bottoms, near coral reefs and rocky areas. This species has been observed resting on the bottom (Figure 14) or in burrows (Pinto 1970

Abbreviated description.
A species of Opistognathus with the following combination of characters: anterior nostril a short tube without a cirrus on posterior rim; posterior end of maxilla rigid, not produced as a thin flexible lamina; supramaxilla present; subopercle without a broad, fan-like flap; most of nape without sensory pores ( Figure  4C); dorsal fin XI, 12-13, with spines thin and flexible, usually curved distally, tips without pale, slightly swollen tabs, and anterior 5-8 soft rays unbranched; dorsal fin sexually dimorphic, fin rays distinctly higher in large males; anal fin III, 12, with 7-10 anterior rays unbranched; outermost segmented pelvic-fin ray tightly bound to adjacent ray and interradial membrane not incised distally; body with 63-87 oblique scales in longitudinal series; vertebrae 10+16; supraneurals 1; gill rakers 13-17+22-28=35-45; dentary without large canines ( Figure 5C). Head and body brown to greenish-tan; upper lip blue; body with two narrow blue stripes on side; distal margins of dorsal and anal fins with narrow blue stripe; outer margin of caudal fin and outer ray of pelvic fin blue.

Abbreviated description (Brazilian specimens only).
A species of Opistognathus with the following combination of characters: anterior nostril a short tube without a cirrus on posterior rim; posterior end of maxilla rigid, not produced as a thin flexible lamina; supramaxilla present; dorsal-fin spines thin, flexible, usually curved distally, and tips without pale, slightly swollen tabs; subopercle without a broad, fan-like flap; most of nape without sensory pores ( Figure 4D); dorsal fin XI, 14-15, with 6-11 anterior rays unbranched distally; anal fin III, 14-15, with 7-10 anterior rays unbranched; outermost segmented pelvic-fin ray tightly bound to adjacent ray and interradial membrane not incised distally; scales in longitudinal series 66-76; vertebrae 10+17; supraneurals absent; gill rakers 15-20+26-32=41-51; dentary with large lateral canines ( Figure  5D). Life color of adults of the two different color morphs as in Figs. 18-20 and discussed below in Remarks. Distribution. As provisionally recognized, this species is known only from the Brazilian Province including continental localities from the State of Maranhão (0°53'S, 44°17'W) south to Armação de Búzios (22°45'S, 41°59'W) in the State of Rio de Janeiro and oceanic sites of the Vitória-Trindade Seamounts Chain and Fernando de Noronha Archipelago ( Figure 6). It is common in coastal regions, in depths of 10-30 meters, and in oceanic sites of 10-65 meters, associated with rubble and sand bottoms, near coral reefs and rocky areas. Its behavior and life history are similar of that of the Caribbean O. aurifrons (Colin 1971;Colin 1973). In this species the burrows are constructed on sandy or rubble bottoms, near reefs, using small stones, shell or coral fragments. They feed on zooplankton while hovering at a small distance over the substrate during quick incursions and generally retreat tail first into the burrow.   Remarks. Brazilian specimens of Opistognathus aff. aurifrons (n=28) differ from Caribbean O. aurifrons (n=292) in consistently having 17 vs. 16 caudal vertebrae. Bra-zilian fish are represented by two allopatric and slightly different genetic populations (see discussion below in "Phylogenetic relationships of western Atlantic Opistognathus"). Mainland and Vitória-Trindade Seamounts Chain specimens have long pelvic fins that when depressed extend at least to the anal-fin origin (25.7-38.2% SL, mean 30.4%, in 22 specimens 30.4-74.8 mm SL) and in fresh adult specimens the top of the head is yellow, bordered posteriorly by a narrow blue band extending from slightly behind the eye to upper jaw and across the nape; remainder of the head and body greenish-yellow to bluish-yellow (Figures 18-19). Populations from the Fernando de Noronha Archipelago differ in having short pelvic fins that do not extend to the analfin origin (20.1-20.7% SL in 2 specimens 58.4-69.2 mm SL) and in fresh adults the head is pale tan-yellow, the body is pale grey-blue, and both are uniformly colored (Figure 20). To further complicate the situation, uncollected juveniles from Fernando de Noronha ( Figure 21) and Bonaire ( Figure 22) have identical life coloration consisting primarily of a white head crossed by diagonal brown-orange stripe about width of pupil extending from chin, through eye and across nape; body and fins pale grey. In preservation, adults from Tobago (USNM 317005) have the same head color pattern and long pelvic fins as those of the Brazilian mainland population but differ in having 16 caudal vertebrae. Unfortunately, life coloration was unrecorded and tissue samples were not obtained. A color photograph taken by Les Wilkes of a "Bluebar jawfish" from St. Vincent, Lesser Antilles (13°15'N, 61°12'W) also looks like mainland Brazilian adults. Overall, there are morphological characters that collectively differentiate the two Brazilian clades from the Caribbean haplotypes (i.e., vertebral counts) and from each other (i.e., pelvic fin length, but note the low sample size), but we know of no consistent phenotypic characters that differentiate the two Caribbean haplotypes from each other. The type locality for O. aurifrons is Dry Tortugas, Florida, making it likely that if the main groups here do indeed represent distinct species, the group containing specimens from Florida (green in Figure 24) represents the true O. aurifrons and the others new species. However, we refrain from making taxonomic changes pending a more thorough analysis comparing multiple genetic loci, and live coloration/morphology of vouchered specimens.
Depending on the locality, adults of Caribbean Opistognathus aurifrons may have relatively short or long pelvic fins, color patterns not found in Brazilian populations or that duplicate them.
Conservation. The conservation status of Brazilian populations of this species has been assessed by the Ministério do Meio Ambiente/Instituto Chico Mendes de Conservação de Biodiversidade (MMA/ICMBio -Brazil) and listed as Least Concern.

Phylogenetic relationships of western Atlantic Opistognathus
The molecular phylogenies inferred from the COI data using ML and Bayesian inference were very similar in topology ( Figure 23); also see supporting information for ML trees. Most basal nodes were not well supported in either analysis, indicating  Two groups in our initial analysis showed distinct phylogenetic structure and geographic genetic variation that suggested the presence of cryptic species. In the first case, specimens initially identified as O. whitehursti from Brazil and the Caribbean each formed two reciprocally monophyletic clades with considerable genetic differentiation in COI (mean between group p-distance = 0.11 (mean within group p-distance ≤ 0.003, Table 2). Subsequent analysis of coloration and morphology revealed subtle differences that support the recognition of these mitochondrial lineages as distinct species (see "Comparisons" in O. vicinus description). Opistognathus aurifrons formed four distinct groups , with one large polyphyletic grade from the Caribbean, a clade nested with this grade from Aruba and Curacao, a clade from mainland Brazil and Vitória-Trindade Seamounts Chain, and a pair of sequences from Fernando de Noronha Archipelago. Genetic variation in COI was very low within each of these groups (mean p-distance ≤0.006), but moderate between each group (mean p-distance between groups = 0.016-0.045). A haplotype map of the Opistognathus aurifrons complex (Figure 25) confirms the four main clusters of haplotypes, which are separated from one another by at least nine mutations in the partial COI gene. The strong connection between the Trindade and mainland populations is probably related to the stepping-stone process provided by Vitória-Trindade Seamounts Chain (Floeter and Gasparini 2000;Macieira et al. 2015;Pinheiro et al. 2017Pinheiro et al. , 2018.   Previous studies of several populations of Caribbean O. aurifrons based on morphology (Böhlke and Thomas 1961) and genetics (Ho et al. 2012) indicated that despite substantial variation in color pattern within and between populations, only a single species should be recognized. Several other western Atlantic reef fishes, especially small, cryptobenthic fishes like gobies and blennioids, show similar patterns where there is substantial mitochondrial divergence without detectable phenotypic differences Victor 2015). Some examples include the multiple genetic lineages within Bathygobius soporator (Tornabene et al. 2010;Tornabene and Pezold 2011), Malactoctenus triangulatus (Victor 2015), several species of Starksia (Baldwin et al. 2011), and some species in the Tigrigobius (Elacatinus) multifasciatus/ panamensis complex (Victor 2010(Victor , 2014. In these instances, nominal species comprise multiple highly-divergent mitochondrial lineages, each with very little genetic variation within lineages, and no recognizable phenotypic differences between lineages (such groups have been termed "genovariants" by Victor 2015). In these studies, and in most cases of such 'cryptic species' of reef fishes, authors have conservatively refrained from naming them as new species based solely on the presence reciprocally monophyletic mitochondrial lineages. Part of this is for practical reasons; taxonomists often prefer species descriptions to be operational, and thus having observable diagnostic characters is critically important. However, it is also possible that such genetic lineages don't correspond to distinct species, and instead are the result of incomplete lineage sorting, or in the case of allopatric lineages, simply representative of geographic population-genetic structure. For these reasons, we follow convention and refrain from naming the distinct lineages of O. aurifrons, pending additional genetic and phenotypic data. However, for conservation purposes it is important to consider these four lineages separately.