Eustomias macrophthalmus Parr 1927

Eustomias macrophthalmus Parr, 1927

Eustomias macrophthalmus Parr, 1927:67–68 [holotype fig. 39, barbel fig. 36c].—Regan and Trewavas, 1930:93 [barbel fig. 77B, 1 additional specimen; E. micropterygius a doubtful synonym].—Beebe and Crane, 1939:212–213 [type re-examined; no additional specimens].—Morrow and Gibbs, 1964:415–416 [no additional specimens; barbel, fig. 110D].—Rass, 1971:511 [listed in Caribbean Sea].—Parin and Pokhilskaya, 1974:364 [1 specimen from 22°42′N, 66°49′W].

DIAGNOSIS.—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.

DESCRIPTION.—The barbel of E. macrophthalmus is long. Its relative length of 76%–93% SL is reached at least by 79 mm (the smallest specimen examined), after which it does not appear to change with growth in the size range examined (79–111 mm SL). There is some indication of sexual dimorphism in barbel length, with six females (99–111 mm SL) having slightly longer barbels (84%–93% SL) than four males (97–111 mm SL with barbels 79%–87% SL). No other sexually dimorphic barbel characters are apparent. The stem axis is lightly peppered with melanophores or lightly streaked with pigment. One specimen (107.5 mm) has no axis pigment, but the body is also faded.

The single terminal bulb is very large, 4.3%–7.0% SL, and does not change with growth in the size range examined. It is approximately six times longer than wide, an elongate sausage-shaped ellipse. Two specimens (79–99 mm, MCZ 55318) have the distal portion of the bulb transparent with a thin dendritic network, rather than opaque. These bulbs may be still developing or regenerating their distal portions, or they may have been crushed.

A minute, simple terminal filament (less than 1% SL) is present in all except 1 specimen (79 mm). It usually is visible only under magnification.

Four males (97–111 mm) have postorbital organs 1.2–2.4 mm long, which are 1.2%–2.2% SL, 34%–67% of fleshy orbit. This development is reached at a short SL relative to other species of Biradiostomias.

In addition to barbel length and postorbital-organ size, the caudal-peduncle depth appears to be sexually dimorphic, with 4 males examined (97–111 mm) having depths of 1.9–2.1 mm and 5 females (99–111 mm) with depths of 1.6–1.9 mm.

Bulbs of three freshly caught males (97–111 mm), one female (100 mm) and one specimen of undetermined sex (95 mm) were deep purple distally, light purple or yellowish white proximally. The postorbital organs of the males were pink or pinkish white.

SIMILAR SPECIES.—Two other species have long terminal bulbs. In E. leptobolus, the most similar species, the barbel is shorter (46%–49% SL vs. 76%–93%), the terminal bulb has a constriction near its distal tip and is shorter (3.3%–3.5% SL vs. 4.3%–6.6%); it has more IA photophores (57–59 vs. 54–56), and IC photophores (75–77 vs. 72–74) and fewer mandibular teeth (9–10 vs. 11–18); and its fleshy orbit diameter is smaller (1.9%–2.7% SL vs. 2.7%–3.6%). In E. quadrifilis, the bulb length, fleshy orbit diameter, and photophore counts resemble those of macrophthalmus, but it, like leptobolus, has a shorter barbel, and its two pairs of relatively long terminal filaments are distinctive. The differences in counts and orbit diameter could prove less trenchant when more is known about variation in leptobolus.

The remaining species of Biradiostomias with a single, non-bilobate, terminal bulb (hulleyi, precarius, pyrifer, xenobolus, and ioani) have relatively small terminal bulbs, 0.5%–1.5% SL, with the bulb less than three times longer than wide.

Eustomias ignotus also resembles macrophthalmus but has two terminal bulbs in close approximation. If the two bulbs were joined, with no constriction, the bulb of ignotus could be indistinguishable from that of macrophthalmus. The barbel length of E. ignotus, however, is shorter, 43.6% SL vs. 76%–93%.

DISTRIBUTION.—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 (Figure 20).

MATERIAL EXAMINED (4, 6, 2 unsexed).—Holotype: BOC 2035 (, 104.1), 22°31′N, 74°26′W, 0–∼1500 m (10,000 ft wire), 30 Mar 1927.

Non-types: ZMUC P201859 (, 101.2), 17°34′N, 64°56′W, 0–∼150 m (300 mw), 18 Apr 1922. IOAN uncat. ( 102.9), 22°42′N, 66°49′W, 0–180 m, 28 Apr 1962. MCZ 55318 ( 99.3; ?, 81.1), 20°12′N, 65°19′W, 2000–2400, 25 Feb 1954. UMML uncat. (, 111.0), 24°29′N, 74°24′W, 0–400 m, 2220–2320, 25 Jan 1973. ISH 3299/79 (, 98.0), 25°08′N, 67°39′W, 0–1800 m, 0416–0820, 12 Apr 1979. ISH 2296/79 (, 100.4), 25°37′N, 61°56′W, 0–100 m, 2103–2200, 21 Mar 1979. USNM 259650 (?, 94.8), 23°46′N, 58°59′W, 0–1200 m, 1542–1742, 28 Mar 1979. USNM 259649 (, 110.5), 23°55′N, 63°58′W, 0–1800 m, 0358–0803, 8 Apr 1979. USNM 259647 (, 97.1), 26°42′N, 79°31′W, 400–750 m, 1320–1657, 7 Aug 1978. USNM 259648 (, 107.5), 19°56′N, 70°43′W, 0–220 m, 14 Oct 1963.