Fig. 55 — Myctophum spinosum, female, From Sarenas (1954, p. 406, fig. 8). 



Description 



D. 13 (12-14); A. 19 (18-20); P. 14 (12-15); AO 7 (6-8) + 7 (5-8), total 14 (12-15); gill rakers 7 

 (6-8) + 1 + 16 (14-18), total 23 (21-25); vertebrae 39 (37-40). 



Exposed margins of scales strongly ctenoid. As in M. lychnobium, 1 to 3 elongated spines 

 project posteriorly from hind margins of scales overlying the AO series of photophores, and 

 often on those over the ventral midline. SAO series slightly but distinctly angulate; SAOi over 

 VO.j.j interspace, usually nearer to VO.^. AOi over second to fourth anal ray base; A0a,.2 

 interspace not greater than those of rest of series. Forebody only moderately deep, about 5 in 

 SL. Body color light to warm brown in preservative. 



From about 55 mm on, males bear 6 (5-7) luminous scales in the supracaudal gland, each 

 with a black rim, and females bear 1 to 4 smaller scales in the infracaudal gland. Specimens 

 from the South China Sea, Philippine, Sulu, and Celebes Seas show a high incidence of both 

 supracaudal and infracaudal glands on one individual; of the 35 specimens used in this study, 

 14 (40% ) bore both glands. In these cases the supracaudal luminous scales numbered from 1 to 

 3. 



Size: To about 90 mm. 



Least depth of capture: At surface at night. 



Distribution: Tropical waters of Pacific, Indo-Pacific, Indian, and possibly Atlantic Oceans 

 ( Wisner, 1970a). Not found in the extreme eastern Pacific but has been reported from the 

 Hawaiian region. 

 Discussion 



Myctophum lychnobium is usually separable from M. spinosum by the more straight and 

 steeply angled SAO series and the position of SAO, more nearly over VO4. However, in the 

 Hawaiian area some specimens presumed to be M. lychnobium have a more angulate SAO 

 series and the first SOA about over a midpoint between VO;, and 4, conditions approaching 

 those characters presumed to be characteristic of M. spinosum. At present it is not known 

 whether these are local variations or, possibly, the result of hybridization. Studies of adequate 

 material from throughout the total range may show the existence of but one highly variable 

 species. 



Some authors have placed M. lychnobium in synonymy with M. spinosum but Moser and 

 Ahlstrom ( 1974) show the larvae of these two species to be distinctively different. 



60 



