Nannobrachium gibbsi Zahuranec 2000

Nannobrachium gibbsi

Lampanyctus achirus.—Craddock and Mead, 1970:28 [in part] [southeast Pacific].—[Not Andriashev, 1962.]

Lampanyctus (Lampanyctus) niger.—Bekker, 1983:87–89, 198–200 [?in part] [key, description, distribution].—[Not Günther, 1887.]

TYPE SPECIMENS.—Holotype: Female 107.5 mm; ZMUC Dana sta 3570 I, 14°01′S, 147°51′W, 10 July 1928.

Paratypes: SIO 72-303, 1 (122 mm); SIO 72-306, 2 (23–54 mm); SIO 72-312, 2 (62–62 mm); SIO 72-313, 3 (31–111 mm); SIO 72-316, 2 (29–29 mm); SIO 72–320, 1 (117 mm); SIO 75-631, 1 (32 mm); UBC 13, 1 (93 mm); USNM uncat. (16°S, 168°04′W, 7 Dec 1967), 1 (89 mm); USNM 298168, 1 (93 mm); USNM 303311, 5 (38–59.5 mm); ZMUC 35-761, 1 (104 mm); ZMUC 35-858, 2 (98–99 mm); ZMUC 35-862, 1 (47 mm); ZMUC 35-879, 1 (74 mm); ZMUC 35-881, 1 (81 mm).

COMPARATIVE DIAGNOSIS.—Nannobrachium gibbsi (Figure 7) can be distinguished from the other species of the Nigrum group primarily by its gill raker count (total 13–15) and number of tooth patches on the lower limb of the second gill arch (7–8) (both lower than in N. atrum and N. nigrum); by the number of AO photophores (13–14), anal-fin rays (17–20), and vertebrae (36–38) (all higher than in N. nigrum and N. indicum); and by the number of lateral line organs (33–35) (lower than in N. atrum but higher than in N. indicum) (Table A1). It can be distinguished from all other species of Nannobrachium by the combination of characters in Table 1 and can be further distinguished from N. crypticum in the Achirus group by its higher number of AO photophores, anal-fin rays, and vertebrae (Table A1).

DESCRIPTION.—Counts are based on up to 62 specimens from the Pacific Ocean and are given in Tables A1–A8. Counts for the holotype are D 15, A 19, P1 13?, 14?, GR 4+10, tooth patches 8, AO 8+6, SC/IC , LL 35?, V 16+21.

Proportions: Given in Table 6. Holotype measurements (in mm) as follows: SL 107.5, HD 16.0, PDD 16.8, CPD 8.9, CPL 21.4, PADL 23.0, PDL 50.4, PPL 42.5, PANL 59.2, PAL 17.1, HL 28.6, UJL broken, SOL 4.8, ED 5.6, SGL 6.5, IGS 12.4, IGEL 12.4, AFB, 26.0, DFB 19.6, AF 10.2.

Fins: Origin of anal fin behind vertical from middle of base of dorsal fin. Pectoral fins with weak and flexible rays, not reaching beyond vertical from PO3, except in small specimens where they may reach beyond PO4. Adipose-fin base above end of anal-fin base, with adipose origin well in advance of end of anal-fin base.

Luminous Organs: PLO 1–2 photophore diameters below lateral line (approximately 2 diameters below in holotype). PO4 slightly below or approximately on level of PVO2 and above or slightly behind a vertical from PO3 (PO4 on level of PVO2 and behind vertical from PO3 in holotype). PVO2 before upper edge or center of pectoral-fin base (PVO2 before upper edge in holotype); PVO1–2 interspace – of PVO2–PLO distance (approximately in holotype). VLO 1–2 photophore diameters below lateral line (two diameters below in holotype). SAO2 above but variable in relation to vertical from AOa1 (SAO2 before vertical from AOa1 in holotype). AOa1 not notably depressed; AOa1–2 interspace slightly enlarged. AOp1 behind end of anal-fin base. Prc well separated from AOp; Prc1–2 on horizontal line; Prc3–4 on or nearly on vertical line, well behind Prc2 although Prc3 occasionally forward as much as a full photophore diameter before vertical from anterior margin of Prc4 (Prc3 on vertical through anterior margin of Prc4 in holotype). Supracaudal and infracaudal luminous glands well developed, infrequently with single separated luminous scale preceding solid infracaudal gland. No secondary photophores found.

Size: The largest known specimen is 122 mm.

Material: 190 (17–120 mm) specimens not designated as type material were examined.

VARIATION.—Nannobrachium gibbsi occurs mainly in the tropical Pacific (Figure 5). Examination of material from the extreme eastern and western ends of its range revealed no consistent variation.

ETYMOLOGY.—It is a pleasure to name this species after the late Dr. Robert H. Gibbs, Jr., of the Smithsonian Institution, in honor of his many contributions to our understanding of open-ocean midwater ichthyology. It is particularly appropriate in this case because he was first, as far as I am aware, to recognize the distinctness of specimens of this species.