Eustomias (Dinematochirus) minimus Clarke 1999
Creators: name: Villarins, Bárbara T
name: Fischer, Luciano G
name: Prokofiev, Artem M
name: Mincarone, Michael M
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Stomiiformes
Stomiidae
Eustomias
Eustomias minimus

description: Eustomias (Dinematochirus) cf. minimus Clarke, 1999
(Figs 6, 8, 9; Tables 1 and 2)
Eustomias minimus Clarke 1999: 1010, figs 2B, 3 [original description, central and western equatorial Pacific; holotype: USNM 3246460].
Eustomias dendriticus. – Parin and Pokhilskaya 1974: 333 [in part, RV Vitiaz: stations 6033/132, 6429/55, and 6429/211]. – Parin 1976: 198 [same specimens as above].
Eustomias minimus. – Villarins et al. 2022: 51, fig. 15E [off Fernando de Noronha Archipelago, Brazil]. – Eduardo et al. 2022: 6 [off Fernando de Noronha Archipelago, Brazil].
Material examined: NPM 4881, one (60 mm SL), Brazil, off Fernando de Noronha Archipelago, ABRACOS, station AB2#42A, 03°15 ʹ 28″S, 31°48 ʹ 29″W to 03°15 ʹ 28″S, 31°50 ʹ 41″W, 0–780 m, RV Antea, mid-water trawl, coll. Leandro Eduardo, Paulo Travassos, and crew, 27 April 2017, 12:23–12:26 h.
Diagnosis: A species of Dinematochirus with: two pectoral-fin rays, barbel with a single thin simple branch arising from the stem; branch length barely half that of distal portion of barbel (from branch to tip of barbel); terminal filaments simple and short, slightly extending to not reaching beyond bulb tip (Figs 6, 8).
Description: Measurements and counts are based on the specimen NPM 4881 and those (when available) reported by Clarke (1999). Chin barbel shorter than head, 11.0% SL (11.0– 12.7% SL; Clarke 1999), 86.8% HL, with stem, dorsal and part of the lateral portion of terminal bulb pigmented, lighter than rest of body (or dorsolateral surfaces solidly pigmented in the paper by Clarke 1999) (Fig. 6A). Terminal bulb slightly constricted at the edge of the dorsal pigment. Stem branch short (2.5% SL, 19.7% HL) and simple, unpigmented (Figs 6B, 8). Distance from the barbel origin to branch 5.7% SL (44.7% HL); distance from branch to bulb 2.5% SL (18.4% HL); and distance from branch to tip of the bulb (distal barbel) 5.5% SL (42.1% HL). Terminal bulb oval, its length 1.4 times its depth and 1.5 times its width. Bulb length 3% SL (23.7% HL) and bulb depth 2.2% SL (17.1% HL) (Fig. 6B). Two opposite terminal filaments short and simple, extending beyond tip of the bulb (1.2% SL, 9.2% HL). Measurements (as a percentage of BL): distance from barbel base to branch 51.5 (70.0–74.0 in the paper by Clarke 1999); branch length 22.7; bulb length 27.3; bulb depth 19.7; terminal filaments 10.6; distance from branch to bulb 21.2; and distance from branch to tip of the bulb (distal barbel) 48.5. Measurements (as a percentage of distal barbel): barbel base to branch 106.3, branch length 46.9 (50.0–60.0 in the paper by Clarke 1999); bulb length 56.3 (60.0–70.0 in the paper by Clarke 1999); bulb depth 40.6; terminal filaments length 21.9 (4.0–20.0 in the paper by Clarke 1999), and distance from branch to bulb 43.8.
Dorsal-fin rays 21, anal-fin rays 34, pectoral-fin rays two, pelvic-fin rays seven, branchiostegal rays 13, and total vertebrae 67. Linear photophores in the series: BR 10, IP 8, PV 28, VAV 15 (six above anal-fin base), OV 29, VAL 18 (seven above anal-fin base), AC 21, IA 51, IC 72, OA 47, and OC 68 (Table 1). Postorbital organ oval, diagonally directed (1% SL, 7.9% HL). Suborbital organ small, rounded (0.5% SL, 3.9% 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 postorbital organ. A few aggregations of luminous spots near IV. Ventral groove from isthmus to fifth PV (sixth PV in the paper by Clarke 1999).
Five teeth on premaxilla (six to eight in the paper by Clarke 1999), all mobile; second tooth the longest (0.7% SL, 5.3% HL). Nine teeth on dentary (eight in the paper by Clarke 1999), all mobile; second tooth the longest (0.5% SL, 3.9% HL). Teeth on maxilla damaged.
Measurements (as a percentage of SL): body depth 6.3, body width 5.0, dorsal-fin base length 15.0, anal-fin base length 26.7, predorsal length 81.7, preanal length 71.7, prepelvic length 50.0, pelvic–anal distance 20.8, snout to anus 70.0, caudal peduncle length 3.3, caudal peduncle depth 3.0, head length 12.7, snout length 4.2, eye diameter 2.5, interorbital space 3.0, and upper jaw length 10.8. Measurements (as a percentage of HL): snout length 32.9, eye diameter 19.7, interorbital space 23.7, upper jaw length 85.5 (Table 2); PO /Eye 0.4 (0.27–0. 36 in the paper by Clarke 1999) and SO /Eye 0.2.
Colour in alcohol: body light brown, and fin rays and membranes lightly pigmented near base. Eight paired dorsal spots between the occiput and dorsal-fin origin.
Distribution: Eustomias minimus is known from the holotype and three non-type specimens collected in the western and Central Equatorial Pacific, from 200 to 600 m depth (Parin and Pokhils’kaya 1974, Clarke 1999). A single specimen tentatively named as Eustomias cf. minimus is known from off northeastern Fernando de Noronha Archipelago (Brazil), western tropical Atlantic (Villarins et al. 2022, present study; Fig. 9). The specimen from Brazil was collected at 780 m depth, at a water temperature of 4.6°C, salinity 34.4, and dissolved oxygen 3.8 mL/L.
Remarks: The characteristics of the specimen reported here agree with those of E. minimus described by Clarke (1999), especially by its simple barbel morphology, with a single branch arising from the barbel stem, without side filaments, bulblets or swelling, and about one-half the length of the subsequent portion of the barbel (= ‘distal barbel’), and by the simple (without side filaments) and short terminal filaments arising from the bulb. However, the Atlantic specimen differs from those originally described by the following characters: part of the lateral surface of the terminal bulb unpigmented in the proximal portion (vs. all lateral surface solidly pigmented in the proximal portion); five teeth in premaxilla (vs. six to eight); nine teeth in dentary (vs. eight); barbel branch arising at 51.5% BL (vs. 70–74% BL); length of branch 46.9% of distal barbel (vs. 50–60%); bulb length 56.3% of distal barbel (vs. 60–70%); terminal filaments 21.9% of distal barbel (vs. 4–20%); PO 40.0% of eye diameter (vs. 27–36%) (Clarke 1999). Although those differences in the pigmentation and barbel proportions were observed, they might be related to intraspecific variation, which is still not understood owing to the low number of known specimens (one in the Atlantic and four in the Pacific; Clarke 1999). Thus, although further investigations on additional specimens of E. minimus and other species of Dinematochirus are necessary, the specimen reported here is identified tentatively as Eustomias cf. minimus.
The other species with relatively simple branch morphology (couplet 2 in the key by Clarke 1999) do not confer with the specimen examined, which has the short simple terminal filaments (vs. terminal filaments with numerous short bulbous side filaments along their lengths in Eustomias pinnatus Clarke, 1999, western Equatorial Pacific), and a short branch, about one-half the length of the distal barbel (vs. branch length equal or greater than length of distal barbel in Eustomias uniramis Clarke, 1999, Central Pacific, and in smaller specimens of Eustomias monoclonus Regan & Trewavas, 1930, northwestern and western equatorial Atlantic). Also, the dorsolateral portion of the terminal bulb is pigmented in E. minimus (vs. proximal portion of the terminal bulb solidly pigmented around its entire circumference in E. monoclonus, and bulb pigmented dorsally except for a mediodorsal fork or unpigmented streak in E. uniramis) (Clarke 1999).
description: Published as part of 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, pp. 1-17 in Zoological Journal of the Linnean Society 202 (1) on pages 10-13, DOI: 10.1093/zoolinnean/zlad163, http://zenodo.org/record/14552546