FISHERY BULLETIN: VOL. 77, NO, 4 



expressed may have been due to the individual 

 measurer. All postlarval measurements and com- 

 parisons were made by one person (i.e., SL <18 

 mm). The postlarval phase was considered con- 

 cluded at the attainment of a full complement of 

 pigmented photophores (ca. 14-18 mm), at which 

 stage individuals were classified as subadults. 

 Meristic counts were made in accordance with 

 Baird (1971) and vertebral counts included all 

 separated vertebrae with the exception of the 

 urostylar complex. 



SYSTEMATIC REMARKS 



Species Distinction 



Morphological distinctions among species of 

 Sternoptyx are relatively slight and distinctive 

 characters tend to be obscured in allopatric popu- 

 lations, making identification difficult in the 

 absence of other species. As an aid to the iden- 

 tification of specimens with a full complement of 

 photophores (ca. 18 mm SL), the distinctive 

 species characteristics reported by Baird (1971), 

 Haruta and Kawaguchi (1976), and Borodulina 



(1978) are combined and expanded in relation to 

 observed patterns of geographic variation. 

 Characters used in distinguishing the four species 

 are discussed below and each species is illustrated 

 (Figures 2-5). Selected meristic and morphometric 

 data are presented in Tables 2 and 3. Table 4 

 provides a synopsis of characters useful in dif- 

 ferentiating adults and subadults. 



The genus can be divided into two morphologi- 

 cal groups or species pairs. In one, containing S. 

 pseudodiaphana (Figure 2) and S. diaphana (Fig- 

 ure 3), the AN photophores completely fill the 

 anal fin base, the horizontal part of the ventral 

 body margin extends very little posterior to AN, 

 and the posterior anal fin pterygiophores are rela- 

 tively short. The second group, with S. obscura 

 (Figure 4) and S. pseudobscura (Figure 5) is 

 characterized by species having an appreciable 

 extension of the horizontal part of the ventral body 

 margin posterior to AN, long posterior anal fin 

 pterygiophores, and smaller AN and SC (Table 3). 



Within these two groups, species may be readily 

 separated from one another, albeit more through a 

 combination of characters than by virtue of a 

 single one. Sternoptyx pseudodiaphana and S. 



Figure 2.— Sternoptyx pseudodiaphana, 59 mm SL. 



806 



