Eustomias (Nominostomias) ophioglossa, Bárbara & Villarins & Luciano & Fischer & Artem & Prokofiev & Michael & Mincarone, 2024

Villarins, Bárbara T, Fischer, Luciano G, Prokofiev, Artem M & Mincarone, Michael M, 2023, Four new species of dragonfish genus Eustomias (Stomiiformes: Stomiidae: Melanostomiinae) from the western tropical Atlantic, with remarks on Eustomias minimus Clarke, 1999, Zoological Journal of the Linnean Society 202 (1), pp. 1-17 : 7-9

Eustomias (Nominostomias) ophioglossa sp.nov.

( Figs 4 , 7C, D , 9 ; Tables 1 and 2 )

Zoobank registration: urn:lsid:zoobank.org:act: 5169EEEB-FC73-4542-9086-1CE98E6F713C

Eustomias sp . – Villarins et al. 2022: 60 [potential new species; off northeastern Brazil].

Eustomias sp . 1. – Eduardo et al. 2022: 6 [potential new species; off northeastern Brazil].

Holotype: NPM 4878, 162 mm SL, Brazil, off Fernando de Noronha Archipelago, ABRACOS , station AB2#44A, 03°52 ʹ 53″S, 32°17 ʹ 33″W to 03°52 ʹ 13″S, 32°16 ʹ 28″W, 0–850 m, RV Antea, mid-water trawl, coll. Leandro Eduardo, Paulo Travassos, and crew, 28 April 2017, 12:44–13:17 h.

Diagnosis: A species of Nominostomias with IC 78 and OC 70; long chin barbel (71% SL, 500% HL) with two terminal bulbs, very long, simple terminal filament (25.9% SL; 182.6% HL) split close to tip at 87.8% BL, bearing several bulblets of different sizes; axis bifurcated directly behind the second bulb at 62.1% BL ( Figs 4 , 7C ).

Description: Chin barbel very long, extending beyond the anal fin insertion (71% SL, 500% HL), with two oval terminal bulbs of approximately equal size (proximal bulb 1.12 times the distal bulb length) separated by a short interspace (9.6% HL, 115.8% proximal bulb length), inserted at 57.4 and 60.6% barbel length, respectively (Fig. 4). No appendages or photophores on the barbel stem. Stem unpigmented. Axis darkly pigmented to proximal end of second bulb and lightly pigmented to the end of filament. Terminal filament very long (25.9% SL, 182.6% HL), without side branches, with axis bifurcated directly after the distal tip of second bulb at 62.9% of barbel length ( Figs 4C , 7C ), ending in two separate unequal terminations, with the ventral longer and heavily pigmented by large melanophores from the bifurcation (Fig. 4D). A group of six closely set elongate bulblets of different shape and size located below the lower branch of the axis in front of the distal bulb at distance of 1.2 times distal bulb length (8.7% HL, 105.2% proximal bulb length). A large oval bulblet (4.3% HL, 52.6% proximal bulb length) situated on the upper branch of the axis at a distance 1.5 times greater than its length from the previous complex of bulblets ( Figs 4C , 7D ). Six tiny round bulblets on terminal filament; the first underneath the lower axis; second and third on the lower axis; fourth and fifth on the upper axis; and the sixth above the lower axis (Fig. 4D). Distance between proximal and distal bulbs 1.16 times proximal bulb length, 1.29 times distal bulb length.

Dorsal-fin rays 20, anal-fin rays 33, pectoral-fin rays 3, pelvic-fin rays 7, branchiostegal rays 16, an total vertebrae 67. Linear photophores in the series: BR 11, IP 8, PV 32, VAV 19 (seven above anal-fin base), OV 33, VAL 18 (eight above anal-fin base), AC 19, IC 78, and OC 70 (Table 1). Presence of one photophore immediately behind end of premaxilla and one photophore on opercle. Postorbital organ small, oval, directed diagonally (0.8% SL, 5.65% HL). Suborbital organ small, rounded (0.5% SL, 3.5% HL). Small photophores on head and body randomly located. Series of small photophores along the anterior edge of the orbit extending in a straight line above PO; a few aggregations of luminous spots near IV photophores and near base of pelvic-fin rays. No ventral groove.

Sixteen teeth on premaxilla, with second tooth the longest (1.8% SL, 12.6% HL), followed by a sequence of three or four smaller teeth and one longer. Seven fixed teeth: first, second, third, sixth, seventh, 13th, and 14th (Fig. 4B). Twenty-one dentary teeth, with fourth tooth the longest (1.4% SL, 10.0% HL) and probably the second and third are replacement teeth. Nine fixed teeth: third, sixth, eighth, 10th, and 11th–15th (Fig. 4B). Twenty-one teeth on maxilla, comb-like and directed backwards. Gill filaments extending almost beyond gill cover when fixed.

Measurements (as a percentage of SL): body depth (behind head) 8.6, body width (at pelvic insertions) 4.4, dorsal-fin base length 14.8, anal-fin base length 26.5, predorsal length 82.7, preanal length 71.0, prepelvic length 56.8, pelvic–anal distance 14.2, snout to anus 69.1, pectoral-fin length 14.8, pelvic-fin length 14.2, caudal peduncle length 2.3, caudal peduncle depth 1.7, head length 14.2, snout length 3.9, chin barbel length 71.0, terminal filament length 25.9, first bulb length 1.2 and depth 0.5, second bulb length, 1.0 and depth 0.4, group of bulblets 0.7 and depth 0.3, single large bulblet 0.6 and depth 0.3, proximal and distal bulb interspace 1.4, distal bulb to group of bulblets 1.2, group of bulblets to single large bulblet 0.9, eye diameter 2.6, interorbital space 3.6, and upper jaw length 10.5 (Table 2). Measurements (as a percentage of HL): snout length 27.4, upper jaw length 71.9, eye diameter 18.7, interorbital space 25.2, chin barbel length 500, terminal filament length 182.6, first bulb length 8.3 and depth 3.5, second bulb length 7.4 and depth 3.0, group of bulblets length 5.2 and depth 2.2, single large bulblet length 4.3 and depth 2.0, proximal and distal bulb interspace 9.6, distal bulb to group of bulblets 8.7, and group of bulblets to single large bulblet 6.5 (Table 2); SO/eye 0.19 and PO/eye 0.30.

Colour when freshly caught: body black and two terminal bulbs blueish. Colour in alcohol: body dark brown; pelvic-fin rays darkly pigmented; dorsal- and anal-fin rays and membranes lightly pigmented near base.

Distribution: Known only from the type locality, off eastern Fernando de Noronha Archipelago, Brazil (Fig. 9). The holotype was collected at 780 m depth, where the temperature was 4.7°C, salinity 34.5, and dissolved oxygen 3.6 mL/L.

Etymology: The species epithet is created from Greek ‘ophis’ (snake) and ‘glossa’ (tongue) in allusion to the terminal filament splitting at the tip.

Comparison: Like all congeners in subgenus Nominostomias , E. ophioglossa has three pectoral-fin rays, seven pelvic-fin rays, barbel stem unpigmented with no photophore-like structures, presence of bulbs and terminal filament, ventral groove absent, and high counts of serial photophores in comparison to the other three-pectoral-rayed subgenus, Haploclonus (78 IC and 70 OC vs. 65–71 IC and 56–65 OC). However, E. ophioglossa differs from all other species of the genus by having unique barbel morphology, with the axis of the terminal filament bifurcated along all of its length. Eustomias ophioglossa belongs to the group I of Gibbs et al. (1983) owing to the presence of two terminal bulbs and a single terminal filament lacking branches. In the identification key proposed by Gibbs et al. (1983), Eustomias ophioglossa fits the couplet 18 (interbulbar distance> 2% SL, barbel length 85% SL or shorter, and terminal filament with or without short branches), which includes Eustomias australensis Gibbs, Clarke & Gomon, 1983 , Eustomias austratlanticus Gibbs, Clarke & Gomon, 1983 , and Eustomias bibulbosus Parr, 1927 . However, E. ophioglossa differs from these species by: (i) the presence of a group of fusiform bulblets and a separated large oval bulblet in the basal portion of the terminal filament, splitting close to tip (vs. only tiny bulblets present and filament not splitting); (ii) interbulbar distance 1.3 times distal bulb length (vs. 1.0 times distal bulb length in E. australensis , 2.8–3.0 times distal bulb length in E. austratlanticus , and 2.0–7.8 times in E. bibulbosus ); and (iii) length of distal bulb 0.9 times proximal bulb (vs. distal bulb 1.6 times proximal bulb in E. australensis , distal bulb 1.4–2.1 times proximal bulb in E. austratlanticus , and distal bulb 1.0–1.6 times proximal bulb in E. bibulbosus ). Also, it differs from E. austratlanticus by the longer terminal filament without branches (25.9% SL vs. 10% or shorter, with two short branches near its base), and from E. bibulbosus by the interbulbar distance 1.2 times proximal bulb length (vs. interbular distance 2.3–8.5 times proximal bulb length) and high count of premaxillary teeth (16 vs. 12–13).

Figures

Figure 4. Eustomias (Nominostomias) ophioglossa, holotype, NPM 4878, 162 mm SL, Brazil, off Fernando de Noronha Archipelago, RV Antea, ABRACOS, station. AB2#44A, 03°52ʹ53″S, 32°17ʹ33″W to 03°52ʹ13″S, 32°16ʹ28″W, 0–850 m. A, whole specimen (scale bar: 10 mm). B, representation of dentition (fixed teeth in black; scale bar: 10 mm). C, terminal portion of chin barbel (scale bar: 10 mm). D, complex of bulblets in the terminal filament (scale bar: 1 mm). E, tip of the terminal filament (scale bar:1 mm). Bulblets are indicated by black arrows.

Figure 7. Chin barbel of the new species of Eustomias. A, terminal portion of Eustomias (Haploclonus) antea, holotype, NPM 4880, 124 mm SL. B, terminal portion of Eustomias (Haploclonus) lucenae, holotype, NPM 4883, 47 mm SL. C, terminal bulbs and complex of bulblets of Eustomias (Nominostomias) ophioglossa, holotype, NPM 4878, 162 mm SL. D, distal bulb and bulblets of Eustomias (Nominostomias) ophioglossa, holotype, NPM 4878, 162 mm SL. E, terminal portion of Eustomias (Nominostomias) bertrandi, holotype, NPM 4610, 109 mm SL. Scale bar: 1 mm.

Figure 9. Sampling location of the Eustomias from off northeastern Brazil:Eustomias antea (square); Eustomias lucenae (circle); Eustomias ophioglossa (triangle); Eustomias bertrandi (triangle); E.cf* minimus (hexagon). Abbreviations: FN, Fernando de Noronha Archipelago; RA, Rocas Atoll; RN, State of Rio Grande do Norte.