Cripplefin Lanternfish

14-16 AO photophores; 9-12 tooth patches on the lower limb of the second gill arch; 34-38 lateral line organs (Ref. 36121). Pectoral fins relatively long and well developed in juveniles (easily visible in individuals up to about 6 cm SL), progressively becoming relatively shorter, with thicker rays, and covered by skin (in various stages of becoming vestigial between 5-8 cm SL). Adults (greater than 8 cm SL) with vestigial rays buried in skin and not externally visible unless skin abraded or otherwise torn (Ref. 36121).

Oceanodromous. Migrating within oceans typically between spawning and different feeding areas, as tunas do. Migrations should be cyclical and predictable and cover more than 100 km.

Dorsal spines (total): 0; Dorsal soft rays (total): 13 - 16; Analspines: 0; Analsoft rays: 15 - 19; Vertebrae: 36 - 38

Oceanic (Ref. 4479) and mesopelagic (Ref. 75154). Usually found below 500 m at night but shallower in upwelling regions.

Nannobrachium achirus (Andriashev, 1962)

Lampanyctus ater.—Norman, 1930:331 [subantarctic South Atlantic].—[Not Tåning, 1928.]

Lampanyctus achirus Andriashev, 1962:256–259 [original description, subantarctic South Pacific].—Bekker, 1964:474 [in part?] [zoogeography]; 1967a: 116 [in part?] [southwest Atlantic].—Bussing, 1965:203–204 [in part?] [geographical variability].—Nafpaktitis and Nafpaktitis, 1969:45–46 [in part] [description, South Indian],—Parin and Andriashev, 1972:885 [zoogeographic relationships].—Krefft, 1974:252 [?in part] [distribution characterized].—Parin et al., 1974:106 [in part?] [southwest Atlantic].—Wisner, 1976:176–180 [in part] [description, distribution, figure].—Paxton, 1979:14 [holotype and paratypes].—Hulley, 1981:182–184 [description, South Atlantic]; 1984a:61, 78–79, fig. 11 [description, off South Africa]; 1986b:240, 242 [zoogeography]; 1986c:306, fig. 86.73 [description, South Africa, figure]; 1989:53 [South Indian, 38°09′39″S, 78°02′63″E]; 1990:162, 163 [figured, Southern Ocean].—McGinnis, 1982:42–44, 66–70 [in part?] [distribution south of 30°S, relationships, zoogeography].—[?] Moser et al., 1984: 238239, fig. 124E [relationships, larva figured from Moser and Ahlstrom, 1974].—Paxton and Hanley, 1989:263 [?in part] [Australian distribution].—Paxton et al., 1995:1315 [listed] [not seen, fide J. Paxton].

Lampanyctus sp. [possibly achirus].—Moser and Ahlstrom, 1974:406–407 [larva figured].

Lampanyctus (Lampanyctus) achirus.—Bekker, 1983:86, 87, 198, 199 [in part] [key, description, distribution].

COMPARATIVE DIAGNOSIS.—Nannobrachium achirus (Figure 18) can be distinguished from all other species in the Achirus group by its higher number of gill rakers and tooth patches on the lower limb of the second gill arch, and from all other species, except N. wisneri, by its higher number of AO photophores, infracaudal luminous gland scales, lateral line organs, and vertebrae (Table A11). It also can be separated from N. wisneri and N. hawaiiensis by the visible presence of pectoral fins in small specimens (up to about 60 mm). Nannobrachium achirus can be distinguished from all other species of Nannobrachium by the combination of characters in Table 1.

DESCRIPTION.—Counts are based on up to 78 specimens and are given in Tables A2–A8, A11.

Proportions: Given in Table 15.

Fins: Origin of anal fin behind vertical from middle of base of dorsal fin. Pectoral fins relatively long and well developed in juvenile stages (easily visible in specimens up to about 60 mm), reaching more than one-half distance to pelvic-fin insertion, progressively becoming relatively shorter, with thicker rays, and covered by skin (in various stages of becoming vestigial between about 50–80 mm). Adults (longer than about 80 mm) with vestigial rays buried in skin and not externally visible unless skin abraded or otherwise torn. In largest adults, vestigial pectoral-fin elements cannot be found (perhaps lost through resorption). Adipose fin over end of anal-fin base.

Luminous Organs: PLO about 2 photophore diameters below lateral line. PO4 approximately on level of PVO2 and above PO3. PVO1_2 interspace wide, that distance 2–3 times into PVO2-PLO distance. SAO1 above VO2_3 interspace, frequently closer to VO3. SAO2 midway above interspace between VO4 and AOa1. SAO3 above AOa1 but somewhat variable in position. AOa1 slightly depressed; AOa1_2 interspace not visibly enlarged. AOp1 above or behind end of anal-fin base. Prc separate from AOp; Prc1_2 on horizontal line; Prc3 below Prc4 but slightly in advance of vertical from center of Prc4. Supracaudal and infracaudal luminous glands well developed, commonly having single separate luminous scale preceding solid infracaudal gland. Secondary photophores in single row on either side of back; single photophore on posterior edge of each scale in first full scale row below middle row of scales; best developed and most prominent in region of adipose fin and less well developed further forward but appear to extend forward to nape.

Size: Nannobrachium achirus is a large-bodied species, reaching a maximum size in excess of 160 mm. The largest specimen recorded by Hulley (pers. comm., 1980) from the South Atlantic was 162 mm. The largest specimen examined in this study was 154 mm.

Material: 451 (30–154 mm) specimens were examined, including the holotype, 124 mm, ZIN 36111, R/V Ob, sta 409, 64°36′S, 108°52′W, 24 April 1958, 1000 m.

VARIATION.—Nannobrachium achirus is a circumglobal, deep-water, subantarctic species (Figure 19). Because it has such a broad distribution, special efforts were made to compare material from the Atlantic, Pacific, and Indian sections of the Southern Ocean, but no patterns of differences were found in the specimens examined.