Myctophum asperum (?) 

 (Richardson, 1844) 



Fig. 56 — Myctophum asperum (?), male 54.7 mm. From the central tropical Pacific Ocean. (Photophores retouched). 



Description 



D. 10-11; A. 17 (16); P. 14 (13-15); AO 6 (7-8) + 6 (4-7), total 13 (11-14); gill rakers 4 + 1 -l- 

 10 (9-12 ), total 15 (14-17); vertebrae 36 (35-38). (Counts given only for specimens from the 

 eastern tropical Pacific Ocean.) 



No elongate sharp spines on the strongly ctenoid exposed scale margins. SAO forming a 

 moderate but distinct angle; SAO, over VO^..^ interspace. Males bear 4 to 6 luminous scales in 

 the supracaudal gland which fill most of the space between end of adipose base and base of first 

 procurrent caudal ray. Females bear 1 or 2 small ovate scales in the infracaudal gland. 



Size: To about 70 mm. 



Least depth of capture: At surface at night. 



Distribution: Fishes corresponding to the diagnosis of M. asperum are known from the 

 northwestern, eastern, central, and southwestern Pacific Ocean, and from the tropical Atlantic 

 and Indian Oceans ( Wisner, 1970a). 

 Discussion 



Myctophum asperum forms a complex of at least two forms in the Pacific Ocean. The 

 holotype has no recorded locality, merely, "habitat — ?"; however, as the collecting vessels 

 (HMS EREBUS and TERROR ) collected primarily in southern seas, it may be assumed that 

 the type locality lies there, but collections could have been made along the entire track 

 (Richardson, 1844). Of the material used in this study, specimens from the east-central tropi- 

 cal Pacific (Fig. 56) appear to differ specifically from those of the tropical Atlantic and from the 

 northwestern Pacific near Japan (Wisner, 1970a) in having fewer anal and pectoral rays, 

 vertebrae, and AOp photophores. Also the two Pacific forms differ in at least 10 characters, 

 with little or no overlap in percent of SL. Superficially, all forms key out to M. asperum, but at 

 this time it is not possible to state which of the Pacific forms, if either, constitutes the true 

 Myctophum asperum . More study on specimens from all oceans is needed. 



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