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The smallest specimen (83 mm) has the relatively shortest barbel (41% of SL). In all others (91–157 mm) barbel is 44%–58% of SL, apparently not changing relative to SL with growth. The stem axis is usually pigmented, variably darkly to very lightly in its proximal portion, becoming lighter or unpigmented distally. A prominent, very dark circular cap is formed at the base of the terminal bulb. The external chevron-shaped or roundish striated areas are unpigmented.
The shape of the terminal bulb is ovoid, usually appearing somewhat block-like. A rounded protuberance projects from 1 side of the distal end, usually with its proximal end constricted. One specimen has an apparently distorted bulb that tapers distally and does not have a well–defined protuberance. The terminal bulb appears to decrease relative to SL. In the smallest specimen, the bulb is 1.2% SL and may represent a stanza of increase. In specimens 91–110 mm SL the bulbs are 1.5%–1.8% SL, in those 113–157 mm they are 0.8%–1.5%.
The terminal filament is 12%–25% SL. An increase relative to SL is suggested, with filaments 12%–16% in 2 specimens 83–91 mm, 13%–18% in 2 110–113 mm, and 14%–25% in 4 125–157 mm. The filament axes are unpigmented in all except 1 specimen, which has a few specks just distad from the bulb. Two long branches arise together just distad of the terminal bulb. Beyond these, there are 1 to 5 prominent, large bulblets, varying in shape from spheroidal to long and either straight-sided or constricted; these bulblets often are large enough to be considered as distal bulbs. Two short branches then arise together, each usually with a single prominent bulblet from which a slender filament arises; in 1 specimen these 2 branches lacked the large bulblets. The main filament and all branches have numerous prominent small bulblets.
The postorbital organ in males 110–125 mm is 0.5%–0.7% SL, 19%–29% of fleshy orbit, and is apparently just beginning to enlarge. In the 4 larger males, 142–151 mm, the organ is 1.7%–1.8% SL, 59%–68% of fleshy orbit.
The mid-anterior edge of the fleshy orbital margin has a slender pedicel extending posteriad over the eye and bearing a white photophore at its tip. Other species of Nominostomias have at most a short pedicel-like extension (e.g., E. gibbsi); most have only a slight bulge from the orbital rim.
A single terminal bulb, 0.8%–1.8% SL, with a nipple–like distal protuberance. Barbel 41%–58% SL. A single, but complex, terminal filament with 2 long branches arising together followed by 2 short branches arising together, each usually with a prominent large bulblet; all branches and the main filament with numerous, prominent small bulblets. Filament length 12%–25% SL. Axis of stem unpigmented or lightly to moderately pigmented; a prominent, wide black circle forming a cap at base of terminal bulb. External chevron-shaped or roundish striated areas unpigmented. Middorsal paired spots between occiput and dorsal-fin origin usually 7, sometimes 8. Anterior margin of fleshy orbit with a distinct slender pedicel extending posteriad over the eye.
One specimen was taken from the northwestern Pacific at 21°N, 144°W. All others are from off Oahu, Hawaiian Islands.
Gibbs RH, Jr, Clarke TA, Gomon JR. 1983. Taxonomy and distribution of the stomioid fish genus Eustomias (Melanostomiidae), I: Subgenus Nominostomias. Smithsonian Contributions to Zoology 380:1–139.
Eustomias pacificus is a member of the subgenus Nominostomias Reagan and Trewavas (1930). The following description applies to all member of Nominostomias.
Three well-developed, free pectoral rays. Seven pelvic rays. Barbel with slender stem having little or no external pigment (axis often pigmented), no row of dark spots, and no branches proximal to the terminal bulbs (E. multifilis may have a few short filaments on the stem near the bulb). One or 2 relatively small terminal bulbs, the distalmost with a projection or filament of variable complexity (the projection almost indiscernible in a few species). No wide ventral body groove posterior to pectoral-fin base (a narrow, shallow groove observed in some specimens). Photophore and vertebral counts high. Photophores in ventral series (IC) 69–80 (seldom fewer than 72, species modes mostly 75–78), in lateral series (OC) 63–73 (seldom fewer than 66, species modes mostly 69–72), VAV and VAL 15–21 (seldom fewer than 16, species modes 17–18 and 18–19, respectively). Vertebrae in continuous series 64–71 (seldom fewer than 65, species modes mostly 67–69). No paired photophores in lateral series. Number of teeth high: premaxillary 11–20, mandibular 14–29 in large specimens (fewer in many specimens less than 100 mm SL).
Counts of fin-rays, photophores, vertebrae, and teeth are of little use in distinguishing most species of Nominostomias, for even those species that show modal differences overlap the ranges of most other species.
None of the body proportions examined by Gibbs et al. (1983) showed convincing differences among species of Nominostomias. Differences in size or relative-growth patterns appeared to characterize a number of species for which few specimens were measured, but these are believed to be artifacts of sampling. The cloud of points of species with abundant measurements usually encompassed those of species with few measurements, and in those abundant species, isometric growth is indicated for almost every body part once metamorphosis is complete. The only body measurement to indicate allometric growth is the least caudal-peduncle depth, which decreases relative to SL.
Gibbs RH, Jr, Clarke TA, Gomon JR. 1983. Taxonomy and distribution of the stomioid fish genus Eustomias (Melanostomiidae), I: Subgenus Nominostomias. Smithsonian Contributions to Zoology 380:1–139.
Regan CT, Trewavas E. 1930. The fishes of the families Stomiatidae and Malacosteidae. Danish Dana Expedition 1920−22 6:1−143.
To at least 157 mm SL.
Northwestern Pacific, west of Oahu, Hawaiian Islands, 21°20'N, 158°20'W, depth 0-170 meters.
Holotype: USNM 223788.
