Nannobrachium idostigma (Parr 1931)

10-14 AO photophores; 8-9 tooth patches on the lower limb of the second gill arch; 31-33 lateral line organs (Ref. 36121). Pectoral fins well developed with rather robust rays (Ref. 36121). Branchiostegal rays: 9-11 (Ref. 31442).

Oviparous (Ref. 31442).

Dorsal spines (total): 0; Dorsal soft rays (total): 13 - 14; Analspines: 0; Analsoft rays: 16 - 20; Vertebrae: 32 - 34

Epipelagic to mesopelagic (Ref. 31442). Oviparous, with planktonic eggs and larvae (Ref. 31442).

Nannobrachium idostigma (Parr, 1931)

Lampanyctus idostigma Parr, 1931:32–34 [original description, eastern tropical Pacific].—Bolin, 1939:138–139 [description, comparison, figure].—Beebe and Van der Pyle, 1944:81 [eastern Pacific].—Bussing, 1965:203–204 [off Peru].—Berry and Perkins, 1966:662 [off Baja California].—Lavenberg and Fitch, 1966:96, 103 [Gulf of California].—Bekker, 1967b:179 [distribution].—Fitch and Brownell, 1968:2567 [otoliths in cetacean stomachs].—Ahlstrom, 1969:42 [California Current larvae]; 1972:1190 [possible larvae from eastern tropical Pacific].—Parin, 1971:82, 86–88, 90 [Peru Current]; 1975:321 [depth of capture at equator].—Robison, 1972:454–455 [Gulf of California].—Brewer, 1973:21–22 [Gulf of California].—Parin et al., 1973: 114–115 [eastern tropical Pacific].—Friedl et al., 1976:611 [deep scattering layer relationship].—Wisner, 1976:173–174 [description, distribution, figure].—Paxton, 1979:14 [holotype and paratypes].—Parin and Bekker, 1981: 66 [zoogeographic relations].—Neighbors and Nafpaktitis, 1982:208–210, 212–214 [lipid composition].—Robison and Craddock, 1983:285–296 [?in part] [Fraser's dolphin food item].—Loeb, 1986:179 [North Pacific depth distribution].—Paxton et al., 1995:1315 [listed] [not seen, fide J. Paxton].

Lampanyctus (Lampanyctus) idostigma.—Fraser-Brunner, 1949:1085 [illustrated key].—Bekker, 1983:84, 85, 194, 196 [key, description, distribution]. Nannobrachium idostigma.—Moser and Ahlstrom, 1996:416–417 [early life history, larvae illustrated].

COMPARATIVE DIAGNOSIS.—Nannobrachium idostigma (Figure 12) can be distinguished from all other species in the Regale group by its lower number of AO photophores, anal-fin rays, infracaudal luminous gland scales, lateral line organs, and vertebrae (Table A9). It can be separated from N. bristori by its low number of AO photophores, tooth patches on the lower limb of the second gill arch, and lateral line organs, and it can be distinguished from all the other species of Nannobrachium by the combination of characters in Table 1.

DESCRIPTION.—Counts are based on up to 25 specimens from the eastern Pacific Ocean and are given in Tables A2–A9.

Proportions: Given in Table 10.

Fins: Origin of anal fin before vertical from middle of base of dorsal fin. Pectoral fins reaching beyond end of pelvic-fin base; well developed with rather robust rays. Base of adipose fin above end of anal-fin base.

Luminous Organs: PLO ;–2 photophore diameters below lateral line. PO4 usually slightly higher than level of PVO2 and behind vertical from PO3. VLO well below lateral line, typically midway between it and pelvic-fin base. SAO1 above VO3–4 interspace; SAO2 variably above AOa1, often slightly before or behind vertical from leading edge of AOa1. Both SAO1 and SAO2 about midway between ventral profile and lateral line. SAO3 approximately over AOa2. AOa1 usually slightly depressed; AOa1–2 interspace slightly enlarged. AOp1 above end of anal-fin base. Pol2 typically well before vertical from origin of adipose fin. Prc usually continuous with AOp. Prc3 usually slightly forward of vertical from Prc4 but low and slightly closer to Prc2. Supracaudal and infracaudal gland scales well developed; no separated scales preceding solid gland. No secondary photophores found.

Size: Wisner (1976) recorded the species to about 90 mm in length, which corresponds closely to the length of 96 mm in the largest specimen examined in this study.

Material: 585 (15–96 mm) specimens were examined.

DISTRIBUTION AND GEOGRAPHIC VARIATION.—Nannobrachium idostigma is restricted to the eastern tropical Pacific (Figure 10). Wisner (1976) reported that this species was taken only in tows that sampled at 300 m or deeper. No evidence could be cited for consistent geographic variation in this species.