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Fish communities on tropical deep reefs are dominated by species that belong to families primarily composed of shallow-water species. Collections of deep-reef fishes via submersibles have allowed us to include these deep-reef species in molecular phylogenies, providing insights into the timing and frequency of invasions from shallow to deep reefs. Here we provide evidence of a new deep-reef invasion in the tribe Gobiosomatini in the family Gobiidae (gobies). We describe two new species, one of which belongs to a new genus, and incorporate these taxa into a time-calibrated molecular phylogeny of Gobiosomatini to show that, collectively, these two genera represent a previously unreported independent invasion on to deep reefs that occurred approximately 20–30 million years ago. These new taxa are readily distinguished from related genera and species by a combination of live coloration, pelvic-fin morphology, meristic characters, head-pore patterns and other osteological characters. We discuss the relevance of these two new species to the systematics of the tribe Gobiosomatini and include a comparison to all known genera in the tribe.

BIRDSONGICHTHYS GEN. NOV. Type species: Birdsongichthys rectus sp. nov. Zoobank registration: urn: lsid: zoobank. org:act: 287F2C89-6296-4FCB-B7B3-ED7B4B4EE73C Diagnosis: Possesses all taxonomic characters present in most members of the Gobiosomatini and the Gobiosoma group, including the following: first dorsal-fin spines VII; dorsal pterygiophore insertion pattern 3-221110; vertebrae 27–11 precaudal and 16 caudal; hypurals 1 and 2 fused to some extent with hypurals 3 and 4 and the terminal vertebral element; one epural; ventral postcleithrum absent. Pelvic fins separate, anterior frenum connecting spines absent, membrane connecting innermost rays absent or weakly developed; pelvic-fin rays 1–5 unbranched and without fleshy or flattened tips; pelvic-fin rays long, extending posteriorly to a point between middle or end of anal fin; side of body covered with ctenoid scales, including two modified basicaudal scales; two anal-fin pterygiophores inserted before first haemal spine; cephalic sensory canals present; second dorsal-fin rays I,9; anal-fin rays I,8; body with three horizontal series of bright yellow spots, one along dorsal midline, one along lateral midline and one along ventral midline; anterior profile of head with gradual slope, not blunt or nearly vertical; eye large (~8.3–10.6% SL). Etymology: The name honours Dr Ray S. Birdsong, who contributed substantially to the knowledge on the systematics of the family Gobiidae, especially taxa from the tropical western Atlantic and eastern Pacific Oceans. The root ‘ichthys’ is derived from the Greek ‘ ikhthús ’ (ιχθύς), fish. Comparisons (Table 1): The presence of VII dorsal spines, 11 + 16 vertebrae and a 3-221110 dorsal pterygiophore pattern (Fig. 4A) all support placement of Birdsongichthys in Gobiosomatini. Gobiosomatini include two main clades, the Microgobius group and the Gobiosoma group. Birdsongichthys shares several characters with genera of the Microgobius group (Antilligobius, Akko Birdsong & Robins, 1995, Bollmannia Jordan, 1890, Microgobius Poey, 1876, Palatogobius and Parrella Ginsburg, 1938), including a laterally compressed body and no substantial fusion between hypurals 3–4 and hypurals 1–2 and the terminal vertebral element. It differs from all Microgobius group genera in having modified basicaudal scales (absent in the Microgobius group) and in having a truncate or emarginate caudal fin (vs. lanceolate in the Microgobius group). The Gobiosoma group contains four lineages: the Barbulifer subgroup, the Nes subgroup, Aboma Jordan & Starks, 1895 and Robinsichthys. Birdsongichthys can be distinguished from all members of the Barbulifer subgroup (Aruma Ginsburg, 1933, Barbulifer, Elacatinus Jordan, 1904, Evermannichthys Metzelaar, 1919, Ginsburgellus Böhlke & Robins, 1968, Gobiosoma, Ophiogobius Hoese, 1976, Pariah Böhlke, 1969, Risor Ginsburg, 1933 and Tigrigobius Fowler, 1931) and Aboma by its completely separate pelvic fins that lack an anterior frenum and have unbranched rays; the Barbulifer subgroup and Aboma have pelvic fins united to form a complete disc with branched rays. Completely separate pelvic fins also characterize species in the Nes subgroup, except Nes and Gobulus. Birdsongichthys differs from most genera of the Nes subgroup and from Robinsichthys in having cephalic lateralis canals and associated head pores. Among Nes subgroup genera, only Eleotrica Ginsburg, 1933, Gymneleotris Bleeker, 1874, and two species of Chriolepis Gilbert, 1892 possess head pores. Birdsongichthys has unbranched pelvic-fin rays, whereas these three genera all have branched pelvicfin rays. The only Gobiosomatini genera containing species with completely unbranched pelvic-fin rays are the monotypic Paedovaricus Van Tassell et al., 2016 [P. imswe (Greenfield, 1981)] and Varicus (unbranched in specimens of five of ten known species in the genus). Birdsongichthys differs from these two genera in having two (vs. one) anal-fin pterygiophores inserted anterior to the first haemal spine. Finally, Birdsongichthys can be further distinguished from Robinsichthys in having 11 + 16 vertebrae (vs. 11 + 17).

BIRDSONGICHTHYS RECTUS SP. NOV. (FIGS 4A, 5–7) Straightfinned goby (English), gobio de aleta recta (Spanish). Gobiidae genus 2, species 1 Robertson et al., 2020: table 1, supplemental plate S13. Zoobank registration: urn: lsid: zoobank. org:act: 016EDDA3-572B-45CB-8B05-676076400186 Holotype: USNM 442874, 14.1 mm SL female, tissue EUS17221, field number CURASUB 17-21, 151 m depth, rubble patch, south and south-east of R / V Chapman mooring, SW of island, Kay Bay, Sint Eustatius, 17.4566, –62.9791, quinaldine, HOV Curasub and R / V Chapman, Carole Baldwin, Luke Tornabene, Bruce Brandt, 19 April 2017. Table 1 . Continued * genus is not monophyletic. ** See Birdsong et al. (1988) for wide range of vertebral counts and pterygiophore insertion patterns. Abbreviations : D 1, first dorsal fin ; D 2, second dorsal fin; A, anal fin; AP , anal fin pterygiophores. Paratypes: MUVS-V-439, 21.0 mm SL male, tissue ROA18021, field number IDABEL18-01, 213 m depth, sand and limestone rubble, outside Halfmoon Bay, Roatan, Honduras, 16.304384°, –86.598204°, quinaldine sulphate, HOV Idabel, D. Ross Robertson, Rachel Manning, Karl Stanley, 4 June 2018; UW 158074, 18.3 mm female, tissue ROA17004, cleared and stained, field number IDABEL17-01, 192 m depth, outside Halfmoon Bay, Roatan, Honduras, 16.305557°, –86.597669°, quinaldine sulphate, HOV Idabel, Luke Tornabene, Ross Robertson, Karl Stanley, 24 July 2017; UW 158128, 12.0 mm female, tissue ROA18044, field number IDABEL18-03, 241 m depth, sand rubble in rock hole, 16.3043°, –86.5982°, quinaldine sulphate, HOV Idabel, Luke Tornabene, Rachel Manning, Karl Stanley, 6 June 2018; UW 158200, 11.5 mm male, tissue ROA18212, field number IDABEL18-08, 213 m depth, sand at base of limestone, 16.3043°, –86.5982°, quinaldine sulphate, HOV Idabel, Luke Tornabene, Katherine Maslenikov, Karl Stanley, 1 June 2018; USNM 442726, 14.4 mm male, tissue EUS17073, field number CURASUB 17-18, 110 m depth, rubble and sand on wall, dropoff west of R / V Chapman mooring, Gallows Bay, Sint Eustatius, 17.4608°, –63.0179°, quinaldine, HOV Curasub and R / V Chapman, Carole Baldwin, Luke Tornabene, Barbara van Bebber, Jordan Casey, 16 April 2017. Diagnosis: Birdsongichthys rectus is the only known member of the genus, so the species diagnosis is that of the diagnosis of the genus. Description: Morphometric data are presented in Table 2. Median and paired fins: first dorsal fin VII(6), first spine extremely elongate in some specimens, extending posteriorly to point between middle of soft dorsal fin and base of anal fin when flat against body; second dorsal fin I,8*(1) or I,9(5); anal fin I,8*(6); pectoral-fin rays 16*(3), 17 (2), 18(1), extending posteriorly to a vertical through second dorsal-fin ray 2 or 3; pelvic fin I,5* (5), all rays unbranched; pelvic fins well separated, lacking anterior frenum, membrane connecting fifth rays absent or reduced; fourth and fifth pelvic-fin rays approximately equal in length, extending posteriorly to base of anal-fin rays 6–7; tips of pelvic-fin rays not ending in fleshy pads; caudal fin truncate or emarginate; branched caudal-fin rays 12 (4)*, segmented caudal-fin rays 17(5)*, caudal fin broken in many specimens. Scales: Scales on head and nape absent; ctenoid scales on side of body present starting above pectoral fin and continuing to caudal peduncle; lateral scale rows 22–23, transverse scale rows 5, scales counted from three specimens including holotype, scales lost in other specimens; pair of modified ctenoid scales with enlarged cteni present at base of caudal fin, one each at dorsal and ventral margins of fin (Fig. 5); abdomen and chest each with small patch of ctenoid scales. Head: Jaw extending posteriorly to a vertical through anterior margin of eye or midpoint of pupil; anterior naris a short tube, posterior naris an opening flush with snout; cephalic lateralis pores small, pores B′, D(s), E′ present in four specimens, pores B′ extremely small and pore D missing in holotype, pores B′ not visible in paratype UW 158200; eyes large, 30–36% HL, positioned dorsolaterally. Upper jaw with two to three rows of teeth anteriorly, outermost row enlarged widely spaced canines continuing along entire upper jaw to the end of the premaxilla, innermost two rows tightly packed, shorter, and conical, becoming single row posteriorly; lower jaw with three to five rows of teeth anteriorly, outermost row restricted to tip of dentary and slightly larger than innermost rows, innermost rows becoming two rows posteriorly. Sensory papillae not visible on most specimens due to small size of specimens and damage to the face from collection. Genitalia: Male urogenital papilla elongate and pointed; female urogenital papilla short, bulbous or slightly conical. Colour in fresh specimens (Fig. 6): Side of body translucent with iridescent scale margins; three horizontal rows of small, bright yellow spots along flank, spots largest in the bottom row; first row with 12–15 spots starting on nape and continuing along dorsal midline, ending just anterior to caudal-fin base; second row with 13–15 spots starting above pectoral fin and continuing along lateral midline, ending just anterior to caudal-fin base; third row with eight to nine spots starting just anterior to anal-fin origin and continuing along ventral midline, ending just anterior to caudal-fin base; tips of snout and upper and lower jaws with small patch of yellow; eye with upperhalf of iris black, lower-half yellow; a broad, oblique yellow to orange stripe extending from lower-rear part of iris down on to preopercle; remainder of head translucent; pink coloration of red gill arches visible through operculum; pectoral-fin base with yellow spot on yellow upper margin of some specimens; dorsal fins with uniform translucent yellow wash with scattered iridophores, and with a distinct horizontal series of yellow spots along midpoints of spines and rays in some specimens; pectoral fins pale or uniformly translucent yellow; caudal fin faintly translucent yellow with two dark yellow, vertical bars at base; anal and pelvic fins uniformly translucent yellow. Colour in preservation (Fig. 7): Body uniformly pale yellowish, no dark pigmentation remains in any preserved specimens, including those fixed either in 95% ethanol or in formalin followed by storage in 70–75% ethanol. Habitat: Known from 110-241 m depth on sand and rubble substrates situated on or around the base of walls or steep rocky slopes on deep reefs. Distribution: Known from Roatan, Honduras and Sint Eustatius, Caribbean Netherlands. Etymology: The epithet is from the Latin adjective rectus, straight, which refers to the straight, unbranched rays of the pelvic fin.

ROBINSICHTHYS NIGRIMARGINATUS SP. NOV. (FIGS 4B, 8–11) Black-margined goby (English), gobio de margen negro (Spanish). Zoobank registration: urn: lsid: zoobank. org:act: 9D9D60B1-2777-47FC-8CB0-6A7E0F70641C Holotype: USNM 446953, 21.0 mm female, tissue CUR19007, field number CURASUB19-02, 229 m depth, sandy bottom, East of Substation downline, Substation Curaçao, Bapor Kibra, Curaçao, 12.0838°, -68.8991°, quinaldine, HOV Curasub, Carole Baldwin, Luke Tornabene, Tico Christiaan, Sarah Yerrace, 7 May 2019. Diagnosis: First dorsal-fin pterygiophore pattern 3-22111*0 (last pterygiophore lacking an associated dorsal-fin spine; Fig. 4B); VI spines in first dorsal fin; 11 + 17 vertebrae; two modified basicaudal scales; head pores absent; second dorsal fin I,9; anal fin I,9; pelvic fins completely united by membrane to form a round disc with well-developed anterior frenum; pectoral-fin rays 19. Description: Morphometric data are presented in Table 2. Median and paired fins: First dorsal fin VI, no spines elongate; second dorsal fin I,9; anal fin I,9; pectoral-fin rays 19, extending posteriorly to a vertical through second dorsal-fin ray 2 or 3; pelvic fin I,5, all rays branched; pelvic fins connected via membrane forming a complete disk with well-developed anterior frenum connecting pelvic spines (Fig. 8); pelvic fin extending posteriorly to just before anus; tips of pelvicfin rays not ending in fleshy pads; caudal fin truncate; branched caudal-fin rays 14, segmented caudal-fin rays 17. Scales: Scales on head and nape absent; ctenoid scales on side of the body present starting above pectoral fin base and ending at base of caudal fin rays; lateral scale rows 24, transverse scale rows six; pair of modified ctenoid scales with enlarged cteni present at base of caudal fin, one each at dorsal and ventral margins of fin; ctenoid scales present on abdomen, scales slightly larger than those on side of body. Head: Jaw extending posteriorly to a vertical through midpoint of the pupil; anterior naris a short tube, posterior naris an opening with raised rim; cephalic lateralis pores absent; eyes large, 41% HL, dorsolateral. Both jaws with two rows of teeth, teeth thin, straight, pointed and evenly spaces posteriorly, becoming less regularly spaced, slightly more recurved anteriorly, with an occasional tooth in outer row slightly larger than others in row. Sensory papillae arranged as in Figure 9, with four prominent transverse rows, including rows 5i/5s present as a continuous single row. Colour in life (Fig. 10): Body translucent with a silvery sheen, an internal white area around gut; body with five dark bars formed by aggregations of black chromatophores overlaying translucent yellow areas, the first bar strongest and widest, extending from the centre of the base of the first dorsal fin to the lower belly, the second to fifth only on the lower-half of the body, thin, formed by less dense aggregations of tiny black chromatophores, the last bar partly fused to the bar on the base of the caudal fin; upper-body profile with six small, translucent yellow blotches, each with a central area of tiny, black chromatophores, the first blotch between the two dorsal fins, the second under the front of the second dorsal fin, the third under the centre of that fin, the fourth to sixth on the caudal peduncle; two elongate internal areas of dark pigment with yellow tones along the spinal column, a short one under the second body bar, a longer one from third body bar to just behind the fourth body bar, with a suggestion of a third patch above the last body bar; when the fish is laterally oriented (Fig. 10A), the silver sheen of the body is present in irregularly dispersed patches in the translucent areas, when the fish is oriented partly towards the viewer (Fig. 10B) that iridescent colour is greenish silver, distributed in patches between the body bars and between the yellow dorsal-profile blotches, and as a distinct vertical greenish silver bar just before the upper-half of the first dark body bar. Head translucent with silver sheen on cheeks; top rear corner of opercle with a translucent orange patch about half pupil size and a larger patch of tiny, welldispersed, black chromatophores over area of pink gills, an indistinct, irregularly shaped translucent orange patch behind centre of eye extending on to nape; mouth translucent, top jaw with silver sheen and a transverse line of black chromatophores across its centre, an indistinct yellow blotch on the snout immediately behind its centre; iris with most of its anterior and rear part overlaid by a dense silvery yellow sheen, top edge of the eyeball silvery yellow; a curved black bar formed by densely aggregated black chromatophores, passing from upper-rear of iris through the pupil and down to rear corner of the mouth, section of bar under eye with relatively large chromatophores overlaying a translucent yellow area, that bar bounded anteriorly and posteriorly by patches of silver iridescence. Base of caudal fin with long, thin, vertical yellow bar with an aggregation of black chromatophores down its centre that partly fuses with last body bar, fin itself translucent with patches of tiny black chromatophores along interradial membranes – two small patches along top of fin, a subterminal band down upper-half of posterior of the fin; a small, vertical patch of black-dotted yellow pigment just behind upper-half of the basal dark bar; first dorsal fin translucent with a large, horizontally oval, solid black blotch covering the outer third of fin between spines 1 and 5, and extending partly towards spine 6, base of fin with short extension of first yellow and black body bar; base of second dorsal fin with two yellow, black dotted extensions of third and fourth yellow body blotches, a black spot immediately above fin base between first two rays, a small, black-dotted, yellow spot on lower third of the fifth ray and another between bases of last two rays, outer edge of fin with a narrow band of dense black chromatophores on interradial membranes; anal fin translucent with scattered, tiny, black chromatophores on interradial membranes, particularly on anterior twothirds of fin; pectoral fin base translucent with a large greenish silver blotch that extends on to basal one-fifth of fin, base of the dorsal ~8 rays of pectoral fin covered with a yellow, black-dotted blotch; remainder of the fin translucent; pelvic fins translucent with small black dots on interradial membranes. Colour in preservation (Fig. 11): Body pale yellowish; side of head below eye with curved, black, vertical bar formed by densely aggregated black chromatophores ending at rear corner of the mouth; operculum covered with scattered chromatophores; chromatophores more densely concentrated on posterior half, forming vertical bar of pigment that extends dorsally on to and across nape; side of body with four concentrations of chromatophores that form vertical bars, first bar complete and positioned beneath centre of first dorsal fin; second bar positioned below origin of second dorsal fin, not extending to dorsal midline, third and fourth bars positioned over end of anal fin and centre of caudal peduncle, respectively, both bars beginning at lateral midline and extending ventrally to ventral midline; a series four or five small patches of chromatophores along dorsal midline, beginning at origin of second dorsal fin and extending to end of caudal peduncle; a singular vertical row of chromatophores over base of caudal fin rays, followed by a small patch of chromatophores on upper-half of caudal fin on anterior one-third of rays; first dorsal fin with distinct black oval on outer third of fin, and smaller dark black spot on middle of fin that is an extension of vertical bar on body; second dorsal fin with three or four small, isolated dark patches of chromatophores on lower-half of fin, distal margin of fin bordered with dark chromatophores; anal fin uniformly covered with scattering of chromatophores; pelvic and pectoral fin without pigment. Genitalia: Female papillae short and conical; male papilla unknown. Habitat: Collected on open sand bottom at 229 m depth. Distribution: Known only from type locality off southwest coast of Curaçao, Caribbean Netherlands. Etymology: The specific epithetic nigrimarginatus is an adjective (black-margined) formed from the Latin niger, glossy black, and marginatus, bordered, in reference to the black margins on the dorsal and caudal fins. Remarks: The new species is placed in the genus Robinsichthys based on the following characters: first dorsal-fin pterygiophore pattern 3-22111*0, with the last pterygiophore lacking an associated dorsal-fin spine (Fig. 4B); VI spines in first dorsal fin; 11 + 17 vertebrae; two modified basicaudal scales; head pores absent; side of body with ctenoid scales; lack of fusion between hypurals 1–2 and hypurals 3–4 and the terminal vertebral element; body with several narrow, dark bands or saddles, head with dark triangular marking below eye. The new species differs from R. arrowsmithensis, and thus the original description of Robinsichthys, most notably in the following ways: (1) having pelvic fins fused to form a complete disk with well-developed anterior frenum vs. having pelvic fins completely separate, lacking frenum; (2) having a large dark blotch on the margin on the first dorsal fin vs. dorsal fin without blotch; (3) having 19 vs. 21–24 (usually 22–23) pectoralfin rays; and (4) having I,9 elements in both the second dorsal fin and anal fin vs. predominately I,10 (I, 9 in one specimen) in both fins of R. arrowsmithensis. Because R. arrowsmithensis was not included in our phylogenetic analysis, we cannot confirm with molecular data that Robinsichthys is monophyletic with regards to Birdsongichthys, and thus whether a new genus is required for B. rectus. However, there are two characters that we regard as apomorphic for Robinsichthy s that are not present in Birdsongichthys. A count of VI dorsal spines (in most specimens) is unique to Robinsichthys among other Gobiosomatini genera (a reduction from the plesiomorphic state of VII spines). Counts of 11 + 17 vertebrae are also considered apomorphic for Robinsichthys, with these counts also being independently derived in members of the Barbulifer subgroup (Elacatinus and allies). Birdsongichthys possesses neither of these synapomorphies. Birdsongichthys has head pores, while both Robinsichthys do not, but head pores and many other morphological characters that may be useful for defining genera of Gobiosomatini have more complex evolutionary histories and may be of limited phylogenetic utility (see Discussion below)., Published as part of Tornabene, Luke, Manning, Rachel, Robertson, D. Ross, Van Tassell, James L. & Baldwin, Carole C., 2023, A new lineage of deep-reef gobies from the Caribbean, including two new species and one new genus (Teleostei: Gobiidae: Gobiosomatini), pp. 322-343 in Zoological Journal of the Linnean Society 197 (2) on pages 337-340, DOI: 10.1093/zoolinnean/zlac013, http://zenodo.org/record/7622658

Initially described in 1882