Fig. 39 — Supracaudal luminous glands of B. panamense, female, 41.5 mm. 



Description 



D. 13(12-13); A. 21 (20-22); P. 14 (13-15); AO 4 (3-4) + 6 (5-7), total 10 (9-11); gill rakers 9 

 (8-10) + 1 + 18 (16-20), total 28 (26-31); vertebrae 32 (31-33). 



SAO, above level of SAO^. OP2 about on level of pupil. FLO nearer lateral line than to 

 pectoral origin. FLO, VLO, and SAO1.2 from a straight line. Opercular margin laterally pro- 

 duced into a long, pointed flap. 



The relationship of sex and caudal luminous glands in this species is uncommon in myc- 

 tophid fishes. Dissection of 80 specimens with and 80 without supracaudal glands showed that 

 only females bore these glands; males bore no glands, and no specimen bore an infracaudal 

 gland. The supracaudal glands of females are usually two (rarely one or three) small, ovoid, 

 weakly developed spots, lightly bordered with dark pigment (Fig. 39); these spots (easily lost) 

 are evident on females of about 34 mm. 



Size: To about 55 mm. 



Least depth of capture: At surface at night. This species is the "Red-bait" reported by 

 Alverson (1961 ) as forming dense "balls" at the surface in daylight, and being fed upon by 

 yellowfin and skipjack tuna. 



Distribution: B. panamense appears to be a relatively near-shore form confined to the 

 eastern Pacific Ocean, principally between about 25° and 10° N, and to the Gulf of California to 

 about 28° N (Fig. 35); the two localities shown outside the main body of collections may 

 represent strays. 

 Discussion 



In regard to caudal luminous glands, Bolin, (1939, fig. 13) stated: "One or two small, 

 poorly developed, widely separated infracaudal luminous patches at vertical of AOp-Prc in- 

 terspace on a few individuals, presumably females; 1 specimen with a very small indistinct 

 supracaudal luminous patch at the same vertical is a male. In most specimens, even the 

 largest ones, no caudal luminous patches are developed." At odds with my findings, Bolin's 

 specimens were from Japan and Philippine waters and may represent Benthosema pterotum 

 (Alcock, 1890), or a related form. Many authors of studies on eastern Pacific myctophids have 

 used the name pterotum for this species. 



Although quite closely related, it appears that Benthosema panamense from the eastern 

 Pacific Ocean is distinct from its Indian Ocean relative, B. pterotum. As noted by Tuning 

 (1932), the FLO and VLO are consistently somewhat higher and the eyes smaller in B. 

 panamense. Taning also reported the snout of the former to be more pointed, but this may be of 

 limited taxonomic importance as it is not a consistent characteristic. 



Body proportions (Table 6) for 12 specimens each of S. panamense from the eastern Pacific 

 Ocean near the Gulf of California, and of B. pterotum from the northern Indian Ocean near the 

 Gulf of Oman, indicate that only the lengths of orbit and pectoral fins differ appreciably, each 

 being smaller in the eastern Pacific with little or no overlap. 



44 



