Fig. 94 — Diaphus diadematus. (A.) Head of adult female, (B.) Head of adult male. 

 Note pronounced sexual dimorphism. From Taning (1932, p. 137, fig. 9). 



Description 



D. 13-14; A. 13-14; P. 10-12; AO 5 -h 5; gill rakers 5 (4) -h 1 -^ 10 (9), total 16 (15); vertebrae 

 33(34). 



PLO a little nearer pectoral base than to lateral line and before a vertical from that base; 

 VLO much nearer lateral line than to pelvic base. SAO, on level of last 2 VO; SAO spacing 

 about equal. The first 3 Pre nearly on same level, the third sometimes slightly raised; Prcj 

 usually well separated from the rest and nearer lateral line than to ventral profile of caudal 

 peduncle. The very large Vn of males is immediately diagnostic (Fig. 94 B); the small Vn of 

 females (Fig. 94 A) is ovate and under posterior half of orbit. A streak of dark tissue extends 

 along margin of orbit between Dn and Vn and bears one or more tiny dots of luminous tissue, 

 one of which may be enlarged to resemble a third organ; the posteriormost organ may then 

 erroneously be interpreted as an So. 



Size: To 33 mm, largest of 28 specimens; it may be a small species. 



Least depth of capture: To 500 m at night. 



Distribution: Probably circumglobal, mainly in southern waters. It is also known from the 

 Atlantic and Indian Oceans near South Africa and from the Java Trench and Celebes Sea (06° 

 N). 

 Discussion 



The placement o{ Diaphus diadematus in the genus appears to depend on the degree of 

 development and prominence of one of the luminous dots between the Dn and Vn. Fraser- 

 Brunner ( 1949) considered such a dot to be a Vn and placed the species in that group having an 

 So; he stated, "Posterior Vn larger than anterior one, the two separate from each other and 

 from Dn." Of the 28 specimens before me, only five have this dot sufficiently developed to be 

 readily visible and subject to misinterpretation; the dot is quite tiny and barely visible on the 

 remaining specimens. 



Regardless of the degree of development of this luminous dot, I believe the proper place- 

 ment of the species to be nearer Diaphus luetkeni than to those species having abona-fide So, 

 because the elongated Vn of males of D. diadematus is more akin (albeit quite different) to 

 that of D. luetkeni. Also, SAO, is on level of last 2 VO, a character common to D. luetkeni, D. 

 termophilus, D. trachops and D. similis, but not found among those species having an So. 



108 



