MOSER and AHLSTROM: DEVELOPMENT OF SCOPELOPSIS MVLTIPUNCTATUS 



Figure 14. — Dendrogram of Paxton's 

 (1968, 1972) arrangement of genera and 

 tribes in the subfamily Lampanyctinae. 



take their places very properly in the horizontal 

 lines of smaller secondary photophores that cover 

 the body. In these remarkable specimens, the 

 primary photophores appear merely as enlarged 

 members in the meristic series of light organs. 

 Accordingly, it is tempting to speculate that this 

 reflects a possible ancestral stage in the evolu- 

 tion of myctophid photophore patterns. We 

 postulate that the archetypal pattern of light 

 organs in lanternfishes was a generalized ar- 

 rangement consisting of a single unspecialized 

 photophore at the posterior margin of each scale 

 pocket and a series of similar photophores dis- 

 tributed over the head. The progressive enlarge- 

 ment and specialization of certain photophores 

 of the generalized pattern and concurrent dimi- 

 nution or loss of the "secondary" photophores 



would seem a propitious mechanism for adap- 

 tation and subsequent species diversification. 

 The enlargement of photophores in the ventral 

 midline to form a pair of longitudinal rows was 

 universal in the family. Clarke (1963) suggest- 

 ed that these downward oriented photophores 

 emit a continuous light of ambient wavelength 

 which conceals the fish by breaking up its sil- 

 houette, that would otherwise be easily detected 

 by predators hunting from below. This and 

 other theories for the universality of the ventral 

 photophore rows are discussed by McAllister 

 (1967). The placement of the ventral and lat- 

 eral photophores in a pattern unique to each spe- 

 cies is an obvious mechanism for species recog- 

 nition and reproductive isolation (Harvey, 1952, 

 1957; Marshall, 1954; Bolin, 1961). 



561 



