Nannobrachium hawaiiensis Zahuranec 2000

Nannobrachium hawaiiensis

Lampanyctus sp. (no pectorals).—Berry and Perkins, 1966:662 [Pacific off California and northern Mexico].

Lampanyctus niger (Form A).—Clarke, 1973:416–418 [ecology north of Hawaii].—[Not Günther, 1887.]

Lampanyctus achirus Species Complex “northern Pacific” form.—Wisner, 1976:177–180, fig. 166B [in part?] [size, characterization].—[Not Andriashev, 1962.]

Lampanyctus niger.—Parin et al., 1977:122, 123 [in part?] [western Pacific].—[Not Günther, 1887.]

Lampanyctus “lacks pectorals” (sp. nov. A).—Loeb, 1979a: 178, 186 [in part?] [larvae, central North Pacific]; 1979b:780–782, 783 [in part?] [larval depth distribution]; 1980:192–195, 199 [in part?] [central Pacific larval distribution].

Lampanyctus (sp. 1).—Fujii, 1984:69, pl. 66-N [description, distribution].

Lampanyctus sp.—Moser et al., 1984:238, fig. 124F.

Lampanyctus (sp. A).—Clarke, 1987:63, 65 [biogeography in central Pacific].

Nannobrachium “no pectorals”.—Moser and Ahlstrom, 1996:420–421 [early life history and larvae illustrated].

TYPE SPECIMENS.—Holotype: Male, 63 mm, SIO 71-300, Aries Expedition, sta 9, 27°24.5′N, 155°25.5′W to 27°24.9′N, 155°13.7′W, 30 September 1971.

Paratypes: HIMB 70–1221, 76 (28–70 mm); HIMB 71-22, 18 (34–70 mm); HIMB 71-617, 32 (35–60 mm); HIMB 71-618, 62 (22–70 mm); HIMB 71-622, 22 (21–62 mm); HIMB 71-631, 30 (36–69 mm); LACM 30–988, 1 (72 mm); LACM 92–6216, 1 (57 mm); OS 012814, 5 (28–68 mm); SIO 71-300, 3 (14–69 mm).

COMPARATIVE DIAGNOSIS.—Nannobrachium hawaiiensis (Figure 21) can be distinguished from all species in the Achirus group, except N. crypticum, by its lower number of AO photophores, infracaudal luminous gland scales, lateral line organs, and vertebrae (Table A11). It can be separated from N. achirus and N. phyllisae by its lower number of gill rakers and tooth patches on the lower limb of the second gill arch. It can be distinguished from all species, especially from N. crypticum, by the complete absence of pectoral fins through the juvenile and adult states. It also can be separated from N. crypticum by its higher number of gill rakers and tooth patches on the lower limb of the second gill arch. Nannobrachium hawaiiensis can be separated from all other species of Nannobrachium by the combination of characters in Table 1, but especially by the absence of pectoral fins.

DESCRIPTION.—Counts are based on up to 26 specimens and are given in Tables A2–A8, A11. Counts for the holotype are D 14, A 16, P1 none, GR 4+11, tooth patches 9, AO 5+7, SC/IC , LL 33, V 15+20.

Proportions: Given in Table 17. Holotype measurements (in mm) as follows: SL 63, HD 10.2, PDD 10.1, CPD 4.8, CPL 14.0, PADL 10.4, PDL 30.6, PPl 24.5, PANL 33.3, PAL 8.6, HL 18.0, UJL 13.6, SOL 2.7, ED 4.7, SGL 3.3, IGS 4.9, IGEL 4.9, AFB 13.7, DFB 11.2, AF 5.6.

Fins: Origin of anal fin below middle of base of dorsal fin. Pectoral fins completely lacking in juvenile, subadult, and adult stages, apparently lost at about time of postlarval transformation. Larvae with enormous, fan-shaped pectorals (Moser and Ahlstrom, 1996:421, figure Myctophidae 17). Pectoral-fin rays present buried in the skin in small juveniles (approximately 25–35 mm). Adipose-fin base over end of anal-fin base.

Luminous Organs: PLO about 2 photophore diameters below lateral line. PO4 approximately on, or slightly below, level of PVO2 (about on level of PVO2 in holotype) and above PO3. PVO1–2 interspace wide, that distance 2–3 times into PVO2-PLO distance (slightly more than 2 times in holotype). SAO1 approximately over VO3 (behind vertical from VO3 in holotype). SAO2 above interspace between VO4 and AOa1 but much closer to AOa1, sometimes over AOa1 (SAO2 before vertical from AOa1 in holotype). SAO3 behind vertical from AOa1. AOa1 not noticeably depressed nor AOa1–2 interspace noticeably enlarged. AOp1 above end of anal-fin base. Prc slightly separate from AOp (notably separate in holotype); Prc1–2 approximately on horizontal line; Prc3 below Prc4 but slightly before vertical from center of Prc4. Supracaudal and infracaudal luminous glands well developed, rarely having single separate luminous scale preceding solid infracaudal gland. Secondary photophores possibly present.

Size: Nannobrachium hawaiiensis is a small-bodied species of Nannobrachium, probably not greatly exceeding 80 mm in length. The longest specimen encountered in this study was 81 mm. Wisner (1976) gave about 70 mm as the maximum size for the “northeastern Pacific form” of the “Lampanyctus achirus Species Complex” and reported that specimens 58–65 mm had well-developed, although immature, ova.

Material: 942 (10–81 mm) specimens, excluding type material.

VARIATION.—Nannobrachium hawaiiensis is the only species of the Achirus group found exclusively in the northern hemisphere. It is restricted to the North Pacific Central water mass (Figure 19). Material was compared from the eastern and western parts of the range, but no consistent geographic variation was evident.

ETYMOLOGY.—The name refers to the Hawaiian Islands near the center of the range, where this species is abundant in the surrounding midwaters.