Nannobrachium crypticum Zahuranec 2000

Nannobrachium crypticum

Lampanyctus “niger”.—Hartmann and Clarke, 1975:637 [in part] [ecology at 39°30N′, 145°].—[Not Günther, 1887.]

Lampanyctus sp. D.—Clarke, 1987:59, 61, 62 [in part] [biogeography in central Pacific].

TYPE SPECIMENS.—Holotype: Female, 87 mm, HIMB TC 47–61, 3°30′N, 145°00′W, 8 February 1970, Thomas A. Clarke, collector.

Paratypes: HIMB 47–52, 40 (28–93 mm); HIMB 47–6, 28 (30–89 mm); HIMB 47–61, 13 (20–87 mm); HIMB 47–67, 31 (23–98 mm); SIO 52-320, 1 (41 mm); SIO 60-236, 3 (31–87 mm); SIO 73-164, 2 (87–90 mm); USNM 303313, 7 (27–61 mm).

COMPARATIVE DIAGNOSIS.—Nannobrachium crypticum (Figure 23) can be distinguished from all other species of the Achirus group by the number of AO photophores, gill rakers, and lower limb tooth patches on the second gill arch (all fewer than in any other species of the Achirus group) (Table A11), and by the presence of externally visible pectoral fins in all life stages (except perhaps in the largest adults—greater than 90 mm). Nannobrachium crypticum is superficially similar to many species in the Nigrum group, but in addition to the differences in Table 1, it can be distinguished from them by the number of gill rakers and lower limb tooth patches on the second gill arch (both lower than in N. nigrum and N. atrum; one fewer gill raker, on average, than in N. indicum), by the number of its AO photophores and vertebrae (both lower than in N. atrum and N. gibbsi), and by the number of infracaudal luminous gland scales and lateral line organs (on average, both higher than in N. indicum; fewer lateral line organs than in N. atrum) (Table A1). Nannobrachium crypticum also can be distinguished from all other species of Nannobrachium by the combination of characters in Table 1.

DESCRIPTION.—Counts are based on up to 99 specimens from the Pacific Ocean and are given in Tables A2–A8, A11. Counts for the holotype are D 13, A 17, P1 12?, GR 4+10, tooth patches 8, AO 5+6 (L), 5+7 (R), SC/IC 3/i+5, LL 32, V 15+19.

Proportions: Given in Table 19. Holotype measurements (in mm) as follows: SL 87, HD 14.4, PDD 12.5, CPD 6.9, CPL 19.2, PADL 18.7, PDL 39.8, PPL 34.3, PANL 47.7, PAL 13.8, HL 25.3, UJL 18.1, SOL 4.4, ED 5.0, SGL 5.3, IGS 8.5, IGEL 10.2, AFB 21.1, DFB 14.6, AF 6.4.

Fins: Origin of anal fin behind vertical through middle of base of dorsal fin. Pectoral fins not reaching beyond PO3, pointing directly downward in larger specimens; rays progressively thicker, stiffer, and relatively shorter in larger specimens but remnants always visible externally, apparently not covered with skin even in 90–100 mm specimens. (Remnant rays in holotype are 2–3 mm long.)

Luminous Organs: PLO 1–2 photophore diameters below lateral line (1 in holotype). PO4 approximately on level of PVO2 (on level in holotype) but somewhat variable and above but slightly behind vertical from PO3. PVO2 before or above middle of pectoral-fin base (above middle in holotype); PVO1–2 interspace – of PVO2–PLO distance (approximately in holotype). VLO within 1 photophore diameter below lateral line. SAO2 midway between VO4 and AOa1, often closer to AOa1 (closer to AOa1 in holotype). SAO3 above, and slightly forward of vertical from AOa1. AOa1 slightly depressed; AOa1–2 interspace slightly enlarged. AOp1 at end of anal-fin base. Prc separated from AOp; Prc1–2 on horizontal line; Prc3–4 on or nearly on vertical, 1 to 2 photophore diameters behind Prc2 (Prc3–4 vertical in holotype, approximately 1 photophore diameter behind Prc2); Prc3 approximately equidistant between Prc2 and Prc4. Pol2 approximately on vertical from adipose-fin origin. Supracaudal and infracaudal luminous glands well developed, infrequently having single separated luminous scale preceding solid infracaudal gland. Secondary photophores seen on back of 1 specimen, 1 photophore near posterior margin of each scale in 2 rows, 1 on either side of dorsal midline in region behind center of dorsal-fin base but additional extent of secondary photophores uncertain.

Size: Nannobrachium crypticum probably reaches a maximum size in excess of 100 mm. The largest specimen encountered in this study was 98 mm.

Material: 252 (19–93 mm) specimens, excluding type material.

VARIATION.—Nannobrachium crypticum is apparently restricted to the equatorial Pacific (Figure 19), where it occurs across the breadth of the ocean from east to west. Variability, which may be geographical, was noted in some meristic characters. In a sample of five specimens taken on expedition Piquero V (lot 137, SIO 69-341) in the southeast portion of the range at 13.5°S, 110.5°W, four specimens had dorsal- and anal-fin ray counts, as well as AO photophore counts, that were at the high end of the range for the species. On the other hand, another sample of six specimens from Piquero V (lot 527, SIO 69-338) taken at 9°S, 108°W, shows little indication of a higher than average number of dorsal- or anal-fin rays or AO photophores. More material is required to clarify whether this variability is significant.

ETYMOLOGY.—The name is derived directly from the Latin adjective crypticum, meaning “obscure” or “hidden,” alluding to the unrecognized existence and relationships of this species.

The Isaacsi Group

The unique character distinguishing the species in this group is the position of the VO2 directly above the VO1 instead of midway between VO1 and VO3 as in all the other groups.

The pectoral-fin development in this group is essentially identical to that of the species in the Cuprarium group except that the pectoral fin is usually slightly longer. Normally, the pectoral fin reaches to or nearly to the pelvic-fin insertion, and the pectoral rays are slightly thicker and stiffer than those of the Cuprarium group.

One other character shared with the species of the Cuprarium group is the position of the Prc3; it is found approximately on a vertical midway between Prc2 and Prc4.

These and other characters are compared in Table 1 for all the species groups of Nannobrachium.

The Isaacsi group contains a single species: N. isaacsi (Wisner, 1974).

Modal characters for N. isaacsi are listed in Table A10 along with the species in the Cuprarium group.