FISHERY BULLETIN: VOL. 77. NO. 4 



Table 4. — Characters useful in differentiating species of the genus Sternoptyx. 



S pseudodiaphana 



S. diaphana 



S. obscura 



S. pseudobscura 



Anal plerygiophore 

 configuration 



SAN position 



Ratio dorsal base 

 to dorsal blade 



Trunk dimensions 



Trunk pigmentation 



Caudal fm 

 pigmentation 



Pectoral fin 

 pigmentation 



Vertebral number 



Anal rays 



Anal photophores 



Eye size 



Dorsal rays 

 Maxinnum size (SL) 



No appreciable pterygio- 

 phore extension posterior 

 to anal photophores {18 

 mm SL) 



About 3 or less times in 

 trunk depth; not more 

 than 3''; times in sub- 

 adults 



Dorsal base normally 

 shorter than blade, 

 occasionally about 

 equal to or slightly 

 longer 



Trunk depth about equal 

 to trunk length, in sub- 

 adults often less 



Dark bar above midline, 

 little pigment near 

 midline 



Light pigment streaks at 

 ventral outermost margin 

 ol caudal rays of larger 

 adults (ca. 40 mm) 



Absent in adults: present 

 at ray bases in juveniles 

 and subadults 



30-32, rarely 29 



14-15, rarely 13 



In adults longer than 

 peduncle depth, little 

 horizontal extension of 

 ventral body margin 

 above anal fin 



Orbit diameter greater 

 than suborbital length, 

 rarely less 



9-13. usually 11-12 

 >60 mm 



Similar to S pseudo- 

 diaphana (>18 mm SL) 



More than 3 times in trunk 

 depth more than 4 times 

 in subadults (-ca 17 mm) 



Dorsal base usually less 

 than 9 of blade 



Trunk depth conspicuously 

 greater than trunk length, 

 in subadults can be equal 



Light in region of midline 



Little or no pigment on 

 caudal rays 



Not present 



28. occasionally 27 or 29 

 14-15, occasionally 13 

 Similar to S pseudo- 

 diaphana, anal photo- 

 phores fill pterygio- 

 phore gap' 



Orbit diameter about equal 

 to, often less than, 

 suborbital length 



9-11, usually -11 



<50 mm 



Extension posterior to anal 

 photophores (see Haruta 

 and Kavi'aguchi 1976) 



As in S. diaphana 



Dorsal base longer than 

 dorsal blade 



Trunk depth conspicuously 

 less than trunk length 



Uniformly dark over whole 

 trunk region 



Corona of dark pigment 

 spreading from base of 

 caudal fin rays 



Not present 



30, occasionally 29 



12-13 



Shorter than peduncle 

 depth, body margin ex- 

 tends posteriorly above 

 anal fin 



Orbit diameter usually 

 greater than suborbital 

 length 



9-11. usually <11 



<45 mm 



Similar to S obscura (see 

 Haruta and Kawaguchi 

 1976) 



About IV2 to 2V; times in 

 trunk depth, raised to 

 midtrunk line in Atlan- 

 tic populations 



As in S pseudodiaphana 



Trunk width greater than 

 trunk length 



Nonuniform dark pigment 

 in trunk region 



Dark pigment restricted 

 to innermost margin of 

 caudal fin rays 



Not present 



29. ocasionally 28 or 30 



13-15 



Similar to S obscura 



Orbit diameter less than 

 suborbital length, equal 

 to it 



9-11 



>55 mm 



Atlantic forms of S. diaphana the trunk depth 

 character exhibits overlap particularly in smaller 

 individuals. Likewise, while the SAN depth 

 character is distinctive for S. diaphana and S. 

 pseudodiaphana, there is considerable overlap 

 when Pacific populations of S. pseudobscura are 

 compared with S. pseudodiaphana. The lower po- 

 sition of the SAN photophore has been illustrated 

 by Haruta and Kawaguchi (1976, figure 6) for 

 western Pacific forms of S. pseudobscura and can 

 be compared with the Atlantic form illustrated 

 here (Figure 5). Differences in vertebral number 

 between Pacific and tropical Atlantic forms of S. 

 pseudodiaphana are indicated (Table 2) and the 

 character should be useful in distinguishing the 

 Pacific population from S. obscura. 



Postlarval Development 



Characters useful in distinguishing later life 

 stages are often less suitable or ineffective for 

 metamorphosing and postlarval stages or indeed 

 small ( <18 mm) subadults. Geographic variation 

 and allometric growth further complicate iden- 

 tification. The present data, while substantiating 



the presence of both allometry and geographic var- 

 iation {Table 3; Figure 7), cannot be considered 

 comprehensive and intensive studies of collections 

 from numerous geographic regions are yet to be 

 done. The extension of the ventral trunk margin, 

 size of AN photophore group, and elongate pos- 

 terior pterygiophores appear to be neotenic 

 characters established from mid- to late- 

 metamorphic stages (Figures 8, 9) and are con- 

 sequently less useful as species-distinctive 

 characters for early life stages. 



When present, the location of photophore SAN 

 is diagnostic, though the placement tends to be 

 somewhat lower on the body in postlarvae. SAN is 

 closely associated with photophores AN in S. 

 diaphana and not markedly raised in S. obscura. 

 For S. pseudodiaphana and S. pseudobscura it is 

 vertically separated from the AN group. In Atlan- 

 tic populations of S. pseudobscura the photophore 

 SAN is raised to the midtrunk line, distinguishing 

 it from other congeners. The lower SAN position in 

 Indo- Pacific populations of S. pseudobscura make 

 this character less useful in separating it from S. 

 pseudodiaphana. The smaller eye (noted by 

 GiJnther 18871 in S. pseudobscura (Table 3) is 



810 



