Eustomias pacificus Gibbs, Clarke & Gomon 1983

Eustomias pacificus

Eustomias sp. 6.—Parin et al., 1977:102 [Vityaz sta 7380, examined by us].

DIAGNOSIS.—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 near its base, followed by 1 to 5 large bulblets, 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 (Figure 2a).

DESCRIPTION.—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 (gibbsi, Figure 2b); most have only a slight bulge from the orbital rim.

DESCRIPTION OF HOLOTYPE.—Male, 148.0 mm SL. D 24. A 39. PI 3. P2 7. IP 7. PV 34. VAV 18. OV 34. VAL 19. AC 19. IA 59. IC 78. OA 53. OC 72. VAV photophores over anal-fin base 7. Branchiostegal photophores 10. Premaxillary teeth 12 left, 13 right: from anterior to posterior, a moderate fixed tooth followed by a long space, a fixed fang followed by a moderate space, a short-to-long series of 1 fixed and 3 depressible teeth, a short-to-moderate series of 3 depressible teeth, and 4 short depressible teeth (5 right). Maxilla with 5 short erect teeth and 4 short posteriad-slanting teeth, a toothless space about as long as occupied by the 1st 5 teeth, and about 17 more short, slanting, serra-like teeth. Mandibular teeth 19 on both sides: from anterior to posterior, a very short fixed tooth followed by a moderate space, a fixed fang followed by a moderate space, a long depressible tooth, a very short fixed tooth, 2 long depressible teeth, a short-to-long series of 5 depressible teeth, a short-to-moderate series of 4 depressible teeth, and 4 short depressible teeth. Vertebrae 69.

Measurements (in mm): Predorsal length 122.4; preanal length 100.2, prepelvic length 79.6, head length 16.5, barbel length 70.0, terminal-bulb length 1.9, filament broken, 1st pair of branches at end of terminal-bulb protuberance, distance from 1st pair to 2nd pair of branches 2.3, 1st branches broken, 2nd-branch length 5.8, snout length 5.1, fleshy orbit length 3.8, postorbital-organ length 2.5, lower-jaw length 14.5, upper-jaw length 13.5, depth behind head (greatest depth) 8.8, caudal-peduncle least depth 2.0, pectoral-fin length 26.3, pelvic-fin length 22.3, dorsal-base length 17.5, anal-base length 37.2, longest premaxillary tooth 2.0, longest mandibular tooth 1.8.

Barbel with stem axis moderately peppered proximally, becoming somewhat lighter distally. Two separated black areas of pigment at base of terminal bulb, forming an incomplete circle. External chevron-shaped or roundish striated areas on stem unpigmented. Filament with a few pigment specks proximally, otherwise unpigmented.

Terminal bulb ovoid with a prominent rounded protuberance, constricted at its base, arising from distal end. A pair of branches arising just at end of protuberance, broken, but intact part with closely spaced small bulblets. Beyond these branches a short portion without bulblets, followed by 2 prominent small bulblets and a large, irregularly spheroidal bulblet about half the length of the terminal bulb. Immediately after the large bulblet, a 2nd pair of branches, each with a prominent basal bulblet about two-thirds the length of the preceding large bulblet and a long, filamentous extension. Beyond 2nd pair of branches, filament with several small bulblets before broken tip.

Paired spots along dorsum not counted, because skin was very darkly pigmented.

SIMILAR SPECIES.—Two other single-bulbed species, patulus and gibbsi, and some inconstans, have a single terminal filament, but in all, the filament is shorter and simpler. All other Nominostomias species with single terminal bulbs have 3 or more filaments arising from the bulb or close to it, and these filaments are shorter (15% SL or less, vs. 12% or more in pacificus). No single-bulbed or two-bulbed species of Nominostomias has protuberance from the terminal bulb or has terminal filaments that approach the unique structure of those of pacificus, in which a pair of basal branches is followed by one or more prominent large bulblets and a 2nd pair of branches that usually have quite large basal bulblets.

The only species with a barbel suggestive of pacificus is E. polyaster, which has 2 terminal bulbs and only 2 pectoral rays and is not treated in this paper. The barbel of polyaster has a notched distal bulb that suggests but is not similar to the bulb with protuberance of pacificus, and the terminal filament is complex, with several large bulblets and a variable number of side branches along its length, but the bulblets and branches are not constant in their number and arrangement as are those of pacificus.

DISTRIBUTION.—One specimen was taken from the northwestern Pacific at 21°N, 144°W. All others are from off Oahu, Hawaiian Islands (Figure 43).

ETYMOLOGY.—From the Latin adjective pacificus (peaceful), alluding to the obvious characteristic of the ocean of the same name, to which this species is endemic.

MATERIAL EXAMINED (9 males, 4 females, 4 unsexed).—Holotype: USNM 223788 (, 148), 21°20′N, 158°20′W, 0–170 m, 2346–0135, 5 Oct 1971.

Paratypes (all except AMNH and IOAN specimens from 21°00′–21°20′N, 158°00′–20′W): USNM 223787 (, 151), 0–200 m, 0120–0500, 22 Jun 1971. USNM 223789 (, 145.9), 0–550 m, 0430–0530, 4 July 1978. USNM 223790 (,125), 0–75 m, 0048–0400, 27 Feb 1972. USNM 223791 (, 115), 0–250 m, 0143–0403,6 Oct 1971. USNM 223792 (, 126), 0–140 m, 0035–0252, 16 Jun 1971. USNM 223793 (, 113), 0–120 m, 1953–2310, 12 Nov 1969. USNM 223794 (?, 94), only locality known. USNM 223795 (, 83), 0–450 m, 1535–1802, 9 Nov 1974. BPBM 26418 (, 104), 0–190 m, 1953–2142, 5 Oct 1971. SIO 80–174 (, 109.5), 0–1000 m, 1215–1655, 22 Feb 1978. AMNH 43494 (, 147), ~19°30′N, 156°00′W, taken in 1975. IOAN uncat. (?, 157), 21°17′N, 143°37′E, 0–100 m, 2313–0013, 1 May 1975.

Non-types: USNM 223796 (, 142), 0–425 m, 0730–1010, 9 Jun 1971. USNM 223797 (, 106), 0–~500 m, 0721–1028, 25 Sep 1973. USNM 223798 (?, 91), 0–650 m, 0730–1132, 9 Nov 1974. USNM 223799 (?, 71), 0–500 m, 1820–2023, 29 Aug 1973.