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Barbel length is 58%–78% SL and does not appear to change with growth. The axis of the stem is darkly pigmented in the two larger specimens, one having streaky pigment, the other densely peppered with large melanophores that merge together. The axis of the small holotype is relatively densely peppered with faded melanophores until close to the bulb, where the density decreases.
The external chevron-shaped or roundish striated areas on the stem are unpigmented. The single bilobate bulb appears to increase slightly in relative size to SL, from 0.9%–1.3% SL. The thick ovoid lobe of the bulb is equal to or slightly longer than the slender, cylindrical, filament–bearing lobe. The notch between lobes is very deep, resulting in the bulbs of the two larger specimens being divided almost completely. Numerous, short filaments (0.3%–1.4% SL) arise from the tip of the slender, cylindrical lobe of the bulb. The smallest specimen (78.1 mm) has the relatively longest filaments, 1.4 times bulb length. The large specimens (136.4 mm and 185 mm) have filaments 33%–50% bulb length, stuck closely together, some have side branches. Under high magnification they appear to be filled with a granular material.
Relative size of the sexually dimorphic postorbital organ is unknown. Nine pairs of subcutaneous spots along the dorsum, the last one under the dorsal fin, were counted in two specimens. Parr (1927) described bulb color of the 78.1 mm holotype (sex undetermined) as having a "roseous" pear-shaped lobe and a "whitish" slimmer lobe.
A single very large, elongate terminal bulb 4.3%–7.0% SL, approximately 6 times longer than wide, without any constriction. Terminal filament, when present, minute and simple. Barbel long, 76%–93% SL. Stem axis lightly pigmented. External chevron–shaped or roundish striated areas on stem not pigmented. Serial photophores: PV 31–34, OV 32–34, IA 54–56, IC 72–74. Vertebrae 63–66. Paired dorsal spots between occiput and dorsal-fin origin 8.
A single very large, elongate terminal bulb 4.3%–7.0% SL, approximately 6 times longer than wide, without any constriction. Terminal filament, when present, minute and simple. Barbel long, 76%–93% SL. Stem axis lightly pigmented. External chevron–shaped or roundish striated areas on stem not pigmented. Serial photophores: PV 31–34, OV 32–34, IA 54–56, IC 72–74. Vertebrae 63–66. Paired dorsal spots between occiput and dorsal–fin origin 8.
Specimens have been taken in the Southern Sargasso Sea, the Straits of Florida, and in the West Indies from the Bahamas to the Virgin Islands.
Gomon JR, Gibbs RH, Jr. 1985. Taxonomy and distribution of the stomioid fish genus Eustomias (Melanostomiidae), II: Biradiostomias, new subgenus. Smithsonian Contributions to Zoology No. 409:1–58.
Eustomias macrophthalmus is a member of the subgenus Biradiostomias Gomon and Gibbs (1985). Biradiostomias differs from all other subgenera of Eustomias (see Gibbs et al., 1983) in the possession of two long, separate pectoral rays. Dinematochirus, when pectoral fins are present, also has two pectoral rays, but these are closely bound together in black membrane; furthermore, the species of Dinematochirus have a well–developed ventral body groove that extends beyond the pectoral–fin bases, and the barbel is short, usually with a pigmented stem, and usually with branches arising from the stem well before the terminal bulb. Biradiostomias is most similar to the subgenera Nominostomias, Haploclonus, and Eustomias in possessing a relatively long, slender barbel that has little or no external pigment and in lacking a well–developed ventral groove behind the pectoral bases. These three subgenera have three long, separate pectoral rays. Biradiostomias generally is intermediate in photophore, vertebral, anal–ray, and tooth numbers between the higher counts in Nominostomias and Eustomias and the lower counts of Haploclonus. The subgenus Eustomias is unique in having paired photophores in the lateral series. Gibbs et al. (1983, table 1) compare counts of Haploclonus, Biradiostomias (as "2–pectoral–rays"), and Nominostomias.
The following are characters that apply to all species of the subgenus. Two 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 terminal bulbs. One to three, rarely four, relatively small terminal bulbs, with or without terminal filaments or projections. No wide ventral body groove posterior to pectoral– fin base. Photophores in ventral series (IC) 69–77 (mostly 71–75), in lateral series (OC) 64– 71 (rarely more than 68, species modes mostly 66–68), VAV and VAL 13–19 (seldom more than 17, species modes 15–17 and 16–17, respectively). Usually 4–6 (rarely 7) VAV photophores located over anal–fin base. No paired photophores in lateral series. Vertebrae in continuous series 63–68 (seldom more than 66, species modes mostly 65–66). Anal rays 31–40, usually 33–38. Premaxillary teeth 7–15; mandibular teeth 9–18 (fewer of each in many specimens less than 100 mm 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.
Gomon JR, Gibbs RH, Jr. 1985. Taxonomy and distribution of the stomioid fish genus Eustomias (Melanostomiidae), II: Biradiostomias, new subgenus. Smithsonian Contributions to Zoology No. 409:1–58.
Parr AE. 1927. The stomiatoid fishes of the suborder Gymnophotodermi (Asthronesthidae, Melanostomiatidae, Idiacanthidae) with a complete review of species. Bulletin of the Bingham Oceanographic Collection 3:1–123.
To 185 mm SL.
22°31'N, 74°26'W, 0—1500 m (10,000 ft wire), 30 Mar 1927.
Holotype: YPM 2035
